Add Auction House; Extend uniform HTTP API for TAPAS-Tasks

.github/workflows/build-and-deploy.yml

@@ -29,6 +29,10 @@ jobs:
       run: mvn -f tapas-tasks/pom.xml --batch-mode --update-snapshots verify
     - run: cp ./tapas-tasks/target/tapas-tasks-0.0.1-SNAPSHOT.jar ./target
 
+    - name: Build with Maven
+      run: mvn -f tapas-auction-house/pom.xml --batch-mode --update-snapshots verify
+    - run: cp ./tapas-auction-house/target/tapas-auction-house-0.0.1-SNAPSHOT.jar ./target
+
     - name: Build with Maven
       run: mvn -f app/pom.xml --batch-mode --update-snapshots verify
     - run: cp ./app/target/app-0.1.0.jar ./target  

docker-compose.yml

@@ -41,6 +41,21 @@ services:
       - "traefik.http.routers.tapas-tasks.entryPoints=web,websecure"
       - "traefik.http.routers.tapas-tasks.tls.certresolver=le"
 
+  auction-house:
+    image: openjdk
+    command: "java -jar /data/tapas-auction-house-0.0.1-SNAPSHOT.jar"
+    restart: unless-stopped
+    volumes:
+      - ./:/data/
+    labels:
+      - "traefik.enable=true"
+      - "traefik.http.routers.tapas-auction-house.rule=Host(`tapas-auction-house.${PUB_IP}.nip.io`)"
+      - "traefik.http.routers.tapas-auction-house.service=tapas-tasks"
+      - "traefik.http.services.tapas-auction-house.loadbalancer.server.port=8082"
+      - "traefik.http.routers.tapas-auction-house.tls=true"
+      - "traefik.http.routers.tapas-auction-house.entryPoints=web,websecure"
+      - "traefik.http.routers.tapas-auction-house.tls.certresolver=le"
+
   app:
     image: openjdk
     command: "java -jar /data/app-0.1.0.jar"

tapas-auction-house/.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+charset = utf-8
+indent_style = space
+indent_size = 4
+trim_trailing_whitespace = true
+end_of_line = lf
+insert_final_newline = true

tapas-auction-house/.gitignore

@@ -0,0 +1,33 @@
+HELP.md
+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/

tapas-auction-house/.mvn/wrapper/MavenWrapperDownloader.java

@@ -0,0 +1,117 @@
+/*
+ * Copyright 2007-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import java.net.*;
+import java.io.*;
+import java.nio.channels.*;
+import java.util.Properties;
+
+public class MavenWrapperDownloader {
+
+    private static final String WRAPPER_VERSION = "0.5.6";
+    /**
+     * Default URL to download the maven-wrapper.jar from, if no 'downloadUrl' is provided.
+     */
+    private static final String DEFAULT_DOWNLOAD_URL = "https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/"
+        + WRAPPER_VERSION + "/maven-wrapper-" + WRAPPER_VERSION + ".jar";
+
+    /**
+     * Path to the maven-wrapper.properties file, which might contain a downloadUrl property to
+     * use instead of the default one.
+     */
+    private static final String MAVEN_WRAPPER_PROPERTIES_PATH =
+            ".mvn/wrapper/maven-wrapper.properties";
+
+    /**
+     * Path where the maven-wrapper.jar will be saved to.
+     */
+    private static final String MAVEN_WRAPPER_JAR_PATH =
+            ".mvn/wrapper/maven-wrapper.jar";
+
+    /**
+     * Name of the property which should be used to override the default download url for the wrapper.
+     */
+    private static final String PROPERTY_NAME_WRAPPER_URL = "wrapperUrl";
+
+    public static void main(String args[]) {
+        System.out.println("- Downloader started");
+        File baseDirectory = new File(args[0]);
+        System.out.println("- Using base directory: " + baseDirectory.getAbsolutePath());
+
+        // If the maven-wrapper.properties exists, read it and check if it contains a custom
+        // wrapperUrl parameter.
+        File mavenWrapperPropertyFile = new File(baseDirectory, MAVEN_WRAPPER_PROPERTIES_PATH);
+        String url = DEFAULT_DOWNLOAD_URL;
+        if(mavenWrapperPropertyFile.exists()) {
+            FileInputStream mavenWrapperPropertyFileInputStream = null;
+            try {
+                mavenWrapperPropertyFileInputStream = new FileInputStream(mavenWrapperPropertyFile);
+                Properties mavenWrapperProperties = new Properties();
+                mavenWrapperProperties.load(mavenWrapperPropertyFileInputStream);
+                url = mavenWrapperProperties.getProperty(PROPERTY_NAME_WRAPPER_URL, url);
+            } catch (IOException e) {
+                System.out.println("- ERROR loading '" + MAVEN_WRAPPER_PROPERTIES_PATH + "'");
+            } finally {
+                try {
+                    if(mavenWrapperPropertyFileInputStream != null) {
+                        mavenWrapperPropertyFileInputStream.close();
+                    }
+                } catch (IOException e) {
+                    // Ignore ...
+                }
+            }
+        }
+        System.out.println("- Downloading from: " + url);
+
+        File outputFile = new File(baseDirectory.getAbsolutePath(), MAVEN_WRAPPER_JAR_PATH);
+        if(!outputFile.getParentFile().exists()) {
+            if(!outputFile.getParentFile().mkdirs()) {
+                System.out.println(
+                        "- ERROR creating output directory '" + outputFile.getParentFile().getAbsolutePath() + "'");
+            }
+        }
+        System.out.println("- Downloading to: " + outputFile.getAbsolutePath());
+        try {
+            downloadFileFromURL(url, outputFile);
+            System.out.println("Done");
+            System.exit(0);
+        } catch (Throwable e) {
+            System.out.println("- Error downloading");
+            e.printStackTrace();
+            System.exit(1);
+        }
+    }
+
+    private static void downloadFileFromURL(String urlString, File destination) throws Exception {
+        if (System.getenv("MVNW_USERNAME") != null && System.getenv("MVNW_PASSWORD") != null) {
+            String username = System.getenv("MVNW_USERNAME");
+            char[] password = System.getenv("MVNW_PASSWORD").toCharArray();
+            Authenticator.setDefault(new Authenticator() {
+                @Override
+                protected PasswordAuthentication getPasswordAuthentication() {
+                    return new PasswordAuthentication(username, password);
+                }
+            });
+        }
+        URL website = new URL(urlString);
+        ReadableByteChannel rbc;
+        rbc = Channels.newChannel(website.openStream());
+        FileOutputStream fos = new FileOutputStream(destination);
+        fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
+        fos.close();
+        rbc.close();
+    }
+
+}

tapas-auction-house/.mvn/wrapper/maven-wrapper.properties

@@ -0,0 +1,2 @@
+distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.8.1/apache-maven-3.8.1-bin.zip
+wrapperUrl=https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar

tapas-auction-house/README.md

@@ -0,0 +1,101 @@
+# tapas-auction-house
+
+The Auction House is the part of your TAPAS application that is largely responsible for the interactions
+with the TAPAS applications developed by the other groups. More precisely, it is responsible for
+launching and managing auctions and it is implemented following the Hexagonal Architecture (based on
+examples from book "Get Your Hands Dirty on Clean Architecture" by Tom Hombergs).
+
+Technologies: Spring Boot, Maven
+
+**Note:** this repository contains an [EditorConfig](https://editorconfig.org/) file (`.editorconfig`)
+with default editor settings. EditorConfig is supported out-of-the-box by the IntelliJ IDE. To help maintain
+consistent code styles, we recommend to reuse this editor configuration file in all your services.
+
+## Project Overview
+
+This project provides a partial implementation of the Auction House. The code is documented in detail,
+here we only include a summary of implemented features:
+* running and managing auctions:
+  * each auction has a deadline by which it is open for bids
+  * once the deadline has passed, the auction house closes the auction and selects a random bid
+* starting an auction using a command via an HTTP adapter (see sample request below)
+* retrieving the list of open auctions via an HTTP adapter, i.e. auctions accepting bids (see sample
+  request below)
+* receiving events when executors are added to the TAPAS application (both via HTTP and MQTT adapters)
+* the logic for automatic placement of bids in auctions: the auction house will place a bid in every
+  auction for which there is at least one executor that can handle the type of task
+  being auctioned
+* discovery of auction houses via a provided resource directory (see assignment sheet for
+  Exercises 5 & 6 for more details)
+
+## Overview of Adapters
+
+In addition to the overall skeleton of the auction house, the current partial implementation provides
+several adapters to help you get started.
+
+### HTTP Adapters
+
+Sample HTTP request for launching an auction:
+
+```shell
+curl -i --location --request POST 'http://localhost:8083/auctions/' \
+--header 'Content-Type: application/json' \
+--data-raw '{
+  "taskUri" : "http://example.org",
+  "taskType" : "taskType1",
+  "deadline" : 10000
+}'
+
+HTTP/1.1 201
+Content-Type: application/json
+Content-Length: 131
+Date: Sun, 17 Oct 2021 22:34:13 GMT
+
+{
+  "auctionId":"1",
+  "auctionHouseUri":"http://localhost:8083/",
+  "taskUri":"http://example.org",
+  "taskType":"taskType1",
+  "deadline":10000
+}
+```
+
+Sample HTTP request for retrieving auctions currently open for bids:
+
+```shell
+curl -i --location --request GET 'http://localhost:8083/auctions/'
+
+HTTP/1.1 200
+Content-Type: application/json
+Content-Length: 133
+Date: Sun, 17 Oct 2021 22:34:20 GMT
+
+[
+  {
+    "auctionId":"1",
+    "auctionHouseUri":"http://localhost:8083/",
+    "taskUri":"http://example.org",
+    "taskType":"taskType1",
+    "deadline":10000
+  }
+]
+```
+
+Sending an [ExecutorAddedEvent](src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/ExecutorAddedEvent.java)
+via an HTTP request:
+
+```shell
+curl -i --location --request POST 'http://localhost:8083/executors/taskType1/executor1'
+
+HTTP/1.1 204
+Date: Sun, 17 Oct 2021 22:38:45 GMT
+```
+
+### MQTT Adapters
+
+Sending an [ExecutorAddedEvent](src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/ExecutorAddedEvent.java)
+via an MQTT message via HiveMQ's [MQTT CLI](https://hivemq.github.io/mqtt-cli/):
+
+```shell
+ mqtt pub -t ch/unisg/tapas-group1/executors -m '{ "taskType" : "taskType1", "executorId" : "executor1" }'
+```

tapas-auction-house/mvnw

@@ -0,0 +1,310 @@
+#!/bin/sh
+# ----------------------------------------------------------------------------
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#    https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+# ----------------------------------------------------------------------------
+
+# ----------------------------------------------------------------------------
+# Maven Start Up Batch script
+#
+# Required ENV vars:
+# ------------------
+#   JAVA_HOME - location of a JDK home dir
+#
+# Optional ENV vars
+# -----------------
+#   M2_HOME - location of maven2's installed home dir
+#   MAVEN_OPTS - parameters passed to the Java VM when running Maven
+#     e.g. to debug Maven itself, use
+#       set MAVEN_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000
+#   MAVEN_SKIP_RC - flag to disable loading of mavenrc files
+# ----------------------------------------------------------------------------
+
+if [ -z "$MAVEN_SKIP_RC" ] ; then
+
+  if [ -f /etc/mavenrc ] ; then
+    . /etc/mavenrc
+  fi
+
+  if [ -f "$HOME/.mavenrc" ] ; then
+    . "$HOME/.mavenrc"
+  fi
+
+fi
+
+# OS specific support.  $var _must_ be set to either true or false.
+cygwin=false;
+darwin=false;
+mingw=false
+case "`uname`" in
+  CYGWIN*) cygwin=true ;;
+  MINGW*) mingw=true;;
+  Darwin*) darwin=true
+    # Use /usr/libexec/java_home if available, otherwise fall back to /Library/Java/Home
+    # See https://developer.apple.com/library/mac/qa/qa1170/_index.html
+    if [ -z "$JAVA_HOME" ]; then
+      if [ -x "/usr/libexec/java_home" ]; then
+        export JAVA_HOME="`/usr/libexec/java_home`"
+      else
+        export JAVA_HOME="/Library/Java/Home"
+      fi
+    fi
+    ;;
+esac
+
+if [ -z "$JAVA_HOME" ] ; then
+  if [ -r /etc/gentoo-release ] ; then
+    JAVA_HOME=`java-config --jre-home`
+  fi
+fi
+
+if [ -z "$M2_HOME" ] ; then
+  ## resolve links - $0 may be a link to maven's home
+  PRG="$0"
+
+  # need this for relative symlinks
+  while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+      PRG="$link"
+    else
+      PRG="`dirname "$PRG"`/$link"
+    fi
+  done
+
+  saveddir=`pwd`
+
+  M2_HOME=`dirname "$PRG"`/..
+
+  # make it fully qualified
+  M2_HOME=`cd "$M2_HOME" && pwd`
+
+  cd "$saveddir"
+  # echo Using m2 at $M2_HOME
+fi
+
+# For Cygwin, ensure paths are in UNIX format before anything is touched
+if $cygwin ; then
+  [ -n "$M2_HOME" ] &&
+    M2_HOME=`cygpath --unix "$M2_HOME"`
+  [ -n "$JAVA_HOME" ] &&
+    JAVA_HOME=`cygpath --unix "$JAVA_HOME"`
+  [ -n "$CLASSPATH" ] &&
+    CLASSPATH=`cygpath --path --unix "$CLASSPATH"`
+fi
+
+# For Mingw, ensure paths are in UNIX format before anything is touched
+if $mingw ; then
+  [ -n "$M2_HOME" ] &&
+    M2_HOME="`(cd "$M2_HOME"; pwd)`"
+  [ -n "$JAVA_HOME" ] &&
+    JAVA_HOME="`(cd "$JAVA_HOME"; pwd)`"
+fi
+
+if [ -z "$JAVA_HOME" ]; then
+  javaExecutable="`which javac`"
+  if [ -n "$javaExecutable" ] && ! [ "`expr \"$javaExecutable\" : '\([^ ]*\)'`" = "no" ]; then
+    # readlink(1) is not available as standard on Solaris 10.
+    readLink=`which readlink`
+    if [ ! `expr "$readLink" : '\([^ ]*\)'` = "no" ]; then
+      if $darwin ; then
+        javaHome="`dirname \"$javaExecutable\"`"
+        javaExecutable="`cd \"$javaHome\" && pwd -P`/javac"
+      else
+        javaExecutable="`readlink -f \"$javaExecutable\"`"
+      fi
+      javaHome="`dirname \"$javaExecutable\"`"
+      javaHome=`expr "$javaHome" : '\(.*\)/bin'`
+      JAVA_HOME="$javaHome"
+      export JAVA_HOME
+    fi
+  fi
+fi
+
+if [ -z "$JAVACMD" ] ; then
+  if [ -n "$JAVA_HOME"  ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+      # IBM's JDK on AIX uses strange locations for the executables
+      JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+      JAVACMD="$JAVA_HOME/bin/java"
+    fi
+  else
+    JAVACMD="`which java`"
+  fi
+fi
+
+if [ ! -x "$JAVACMD" ] ; then
+  echo "Error: JAVA_HOME is not defined correctly." >&2
+  echo "  We cannot execute $JAVACMD" >&2
+  exit 1
+fi
+
+if [ -z "$JAVA_HOME" ] ; then
+  echo "Warning: JAVA_HOME environment variable is not set."
+fi
+
+CLASSWORLDS_LAUNCHER=org.codehaus.plexus.classworlds.launcher.Launcher
+
+# traverses directory structure from process work directory to filesystem root
+# first directory with .mvn subdirectory is considered project base directory
+find_maven_basedir() {
+
+  if [ -z "$1" ]
+  then
+    echo "Path not specified to find_maven_basedir"
+    return 1
+  fi
+
+  basedir="$1"
+  wdir="$1"
+  while [ "$wdir" != '/' ] ; do
+    if [ -d "$wdir"/.mvn ] ; then
+      basedir=$wdir
+      break
+    fi
+    # workaround for JBEAP-8937 (on Solaris 10/Sparc)
+    if [ -d "${wdir}" ]; then
+      wdir=`cd "$wdir/.."; pwd`
+    fi
+    # end of workaround
+  done
+  echo "${basedir}"
+}
+
+# concatenates all lines of a file
+concat_lines() {
+  if [ -f "$1" ]; then
+    echo "$(tr -s '\n' ' ' < "$1")"
+  fi
+}
+
+BASE_DIR=`find_maven_basedir "$(pwd)"`
+if [ -z "$BASE_DIR" ]; then
+  exit 1;
+fi
+
+##########################################################################################
+# Extension to allow automatically downloading the maven-wrapper.jar from Maven-central
+# This allows using the maven wrapper in projects that prohibit checking in binary data.
+##########################################################################################
+if [ -r "$BASE_DIR/.mvn/wrapper/maven-wrapper.jar" ]; then
+    if [ "$MVNW_VERBOSE" = true ]; then
+      echo "Found .mvn/wrapper/maven-wrapper.jar"
+    fi
+else
+    if [ "$MVNW_VERBOSE" = true ]; then
+      echo "Couldn't find .mvn/wrapper/maven-wrapper.jar, downloading it ..."
+    fi
+    if [ -n "$MVNW_REPOURL" ]; then
+      jarUrl="$MVNW_REPOURL/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+    else
+      jarUrl="https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+    fi
+    while IFS="=" read key value; do
+      case "$key" in (wrapperUrl) jarUrl="$value"; break ;;
+      esac
+    done < "$BASE_DIR/.mvn/wrapper/maven-wrapper.properties"
+    if [ "$MVNW_VERBOSE" = true ]; then
+      echo "Downloading from: $jarUrl"
+    fi
+    wrapperJarPath="$BASE_DIR/.mvn/wrapper/maven-wrapper.jar"
+    if $cygwin; then
+      wrapperJarPath=`cygpath --path --windows "$wrapperJarPath"`
+    fi
+
+    if command -v wget > /dev/null; then
+        if [ "$MVNW_VERBOSE" = true ]; then
+          echo "Found wget ... using wget"
+        fi
+        if [ -z "$MVNW_USERNAME" ] || [ -z "$MVNW_PASSWORD" ]; then
+            wget "$jarUrl" -O "$wrapperJarPath"
+        else
+            wget --http-user=$MVNW_USERNAME --http-password=$MVNW_PASSWORD "$jarUrl" -O "$wrapperJarPath"
+        fi
+    elif command -v curl > /dev/null; then
+        if [ "$MVNW_VERBOSE" = true ]; then
+          echo "Found curl ... using curl"
+        fi
+        if [ -z "$MVNW_USERNAME" ] || [ -z "$MVNW_PASSWORD" ]; then
+            curl -o "$wrapperJarPath" "$jarUrl" -f
+        else
+            curl --user $MVNW_USERNAME:$MVNW_PASSWORD -o "$wrapperJarPath" "$jarUrl" -f
+        fi
+
+    else
+        if [ "$MVNW_VERBOSE" = true ]; then
+          echo "Falling back to using Java to download"
+        fi
+        javaClass="$BASE_DIR/.mvn/wrapper/MavenWrapperDownloader.java"
+        # For Cygwin, switch paths to Windows format before running javac
+        if $cygwin; then
+          javaClass=`cygpath --path --windows "$javaClass"`
+        fi
+        if [ -e "$javaClass" ]; then
+            if [ ! -e "$BASE_DIR/.mvn/wrapper/MavenWrapperDownloader.class" ]; then
+                if [ "$MVNW_VERBOSE" = true ]; then
+                  echo " - Compiling MavenWrapperDownloader.java ..."
+                fi
+                # Compiling the Java class
+                ("$JAVA_HOME/bin/javac" "$javaClass")
+            fi
+            if [ -e "$BASE_DIR/.mvn/wrapper/MavenWrapperDownloader.class" ]; then
+                # Running the downloader
+                if [ "$MVNW_VERBOSE" = true ]; then
+                  echo " - Running MavenWrapperDownloader.java ..."
+                fi
+                ("$JAVA_HOME/bin/java" -cp .mvn/wrapper MavenWrapperDownloader "$MAVEN_PROJECTBASEDIR")
+            fi
+        fi
+    fi
+fi
+##########################################################################################
+# End of extension
+##########################################################################################
+
+export MAVEN_PROJECTBASEDIR=${MAVEN_BASEDIR:-"$BASE_DIR"}
+if [ "$MVNW_VERBOSE" = true ]; then
+  echo $MAVEN_PROJECTBASEDIR
+fi
+MAVEN_OPTS="$(concat_lines "$MAVEN_PROJECTBASEDIR/.mvn/jvm.config") $MAVEN_OPTS"
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin; then
+  [ -n "$M2_HOME" ] &&
+    M2_HOME=`cygpath --path --windows "$M2_HOME"`
+  [ -n "$JAVA_HOME" ] &&
+    JAVA_HOME=`cygpath --path --windows "$JAVA_HOME"`
+  [ -n "$CLASSPATH" ] &&
+    CLASSPATH=`cygpath --path --windows "$CLASSPATH"`
+  [ -n "$MAVEN_PROJECTBASEDIR" ] &&
+    MAVEN_PROJECTBASEDIR=`cygpath --path --windows "$MAVEN_PROJECTBASEDIR"`
+fi
+
+# Provide a "standardized" way to retrieve the CLI args that will
+# work with both Windows and non-Windows executions.
+MAVEN_CMD_LINE_ARGS="$MAVEN_CONFIG $@"
+export MAVEN_CMD_LINE_ARGS
+
+WRAPPER_LAUNCHER=org.apache.maven.wrapper.MavenWrapperMain
+
+exec "$JAVACMD" \
+  $MAVEN_OPTS \
+  -classpath "$MAVEN_PROJECTBASEDIR/.mvn/wrapper/maven-wrapper.jar" \
+  "-Dmaven.home=${M2_HOME}" "-Dmaven.multiModuleProjectDirectory=${MAVEN_PROJECTBASEDIR}" \
+  ${WRAPPER_LAUNCHER} $MAVEN_CONFIG "$@"

tapas-auction-house/mvnw.cmd

@@ -0,0 +1,182 @@
+@REM ----------------------------------------------------------------------------
+@REM Licensed to the Apache Software Foundation (ASF) under one
+@REM or more contributor license agreements.  See the NOTICE file
+@REM distributed with this work for additional information
+@REM regarding copyright ownership.  The ASF licenses this file
+@REM to you under the Apache License, Version 2.0 (the
+@REM "License"); you may not use this file except in compliance
+@REM with the License.  You may obtain a copy of the License at
+@REM
+@REM    https://www.apache.org/licenses/LICENSE-2.0
+@REM
+@REM Unless required by applicable law or agreed to in writing,
+@REM software distributed under the License is distributed on an
+@REM "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+@REM KIND, either express or implied.  See the License for the
+@REM specific language governing permissions and limitations
+@REM under the License.
+@REM ----------------------------------------------------------------------------
+
+@REM ----------------------------------------------------------------------------
+@REM Maven Start Up Batch script
+@REM
+@REM Required ENV vars:
+@REM JAVA_HOME - location of a JDK home dir
+@REM
+@REM Optional ENV vars
+@REM M2_HOME - location of maven2's installed home dir
+@REM MAVEN_BATCH_ECHO - set to 'on' to enable the echoing of the batch commands
+@REM MAVEN_BATCH_PAUSE - set to 'on' to wait for a keystroke before ending
+@REM MAVEN_OPTS - parameters passed to the Java VM when running Maven
+@REM     e.g. to debug Maven itself, use
+@REM set MAVEN_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000
+@REM MAVEN_SKIP_RC - flag to disable loading of mavenrc files
+@REM ----------------------------------------------------------------------------
+
+@REM Begin all REM lines with '@' in case MAVEN_BATCH_ECHO is 'on'
+@echo off
+@REM set title of command window
+title %0
+@REM enable echoing by setting MAVEN_BATCH_ECHO to 'on'
+@if "%MAVEN_BATCH_ECHO%" == "on"  echo %MAVEN_BATCH_ECHO%
+
+@REM set %HOME% to equivalent of $HOME
+if "%HOME%" == "" (set "HOME=%HOMEDRIVE%%HOMEPATH%")
+
+@REM Execute a user defined script before this one
+if not "%MAVEN_SKIP_RC%" == "" goto skipRcPre
+@REM check for pre script, once with legacy .bat ending and once with .cmd ending
+if exist "%HOME%\mavenrc_pre.bat" call "%HOME%\mavenrc_pre.bat"
+if exist "%HOME%\mavenrc_pre.cmd" call "%HOME%\mavenrc_pre.cmd"
+:skipRcPre
+
+@setlocal
+
+set ERROR_CODE=0
+
+@REM To isolate internal variables from possible post scripts, we use another setlocal
+@setlocal
+
+@REM ==== START VALIDATION ====
+if not "%JAVA_HOME%" == "" goto OkJHome
+
+echo.
+echo Error: JAVA_HOME not found in your environment. >&2
+echo Please set the JAVA_HOME variable in your environment to match the >&2
+echo location of your Java installation. >&2
+echo.
+goto error
+
+:OkJHome
+if exist "%JAVA_HOME%\bin\java.exe" goto init
+
+echo.
+echo Error: JAVA_HOME is set to an invalid directory. >&2
+echo JAVA_HOME = "%JAVA_HOME%" >&2
+echo Please set the JAVA_HOME variable in your environment to match the >&2
+echo location of your Java installation. >&2
+echo.
+goto error
+
+@REM ==== END VALIDATION ====
+
+:init
+
+@REM Find the project base dir, i.e. the directory that contains the folder ".mvn".
+@REM Fallback to current working directory if not found.
+
+set MAVEN_PROJECTBASEDIR=%MAVEN_BASEDIR%
+IF NOT "%MAVEN_PROJECTBASEDIR%"=="" goto endDetectBaseDir
+
+set EXEC_DIR=%CD%
+set WDIR=%EXEC_DIR%
+:findBaseDir
+IF EXIST "%WDIR%"\.mvn goto baseDirFound
+cd ..
+IF "%WDIR%"=="%CD%" goto baseDirNotFound
+set WDIR=%CD%
+goto findBaseDir
+
+:baseDirFound
+set MAVEN_PROJECTBASEDIR=%WDIR%
+cd "%EXEC_DIR%"
+goto endDetectBaseDir
+
+:baseDirNotFound
+set MAVEN_PROJECTBASEDIR=%EXEC_DIR%
+cd "%EXEC_DIR%"
+
+:endDetectBaseDir
+
+IF NOT EXIST "%MAVEN_PROJECTBASEDIR%\.mvn\jvm.config" goto endReadAdditionalConfig
+
+@setlocal EnableExtensions EnableDelayedExpansion
+for /F "usebackq delims=" %%a in ("%MAVEN_PROJECTBASEDIR%\.mvn\jvm.config") do set JVM_CONFIG_MAVEN_PROPS=!JVM_CONFIG_MAVEN_PROPS! %%a
+@endlocal & set JVM_CONFIG_MAVEN_PROPS=%JVM_CONFIG_MAVEN_PROPS%
+
+:endReadAdditionalConfig
+
+SET MAVEN_JAVA_EXE="%JAVA_HOME%\bin\java.exe"
+set WRAPPER_JAR="%MAVEN_PROJECTBASEDIR%\.mvn\wrapper\maven-wrapper.jar"
+set WRAPPER_LAUNCHER=org.apache.maven.wrapper.MavenWrapperMain
+
+set DOWNLOAD_URL="https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+
+FOR /F "tokens=1,2 delims==" %%A IN ("%MAVEN_PROJECTBASEDIR%\.mvn\wrapper\maven-wrapper.properties") DO (
+    IF "%%A"=="wrapperUrl" SET DOWNLOAD_URL=%%B
+)
+
+@REM Extension to allow automatically downloading the maven-wrapper.jar from Maven-central
+@REM This allows using the maven wrapper in projects that prohibit checking in binary data.
+if exist %WRAPPER_JAR% (
+    if "%MVNW_VERBOSE%" == "true" (
+        echo Found %WRAPPER_JAR%
+    )
+) else (
+    if not "%MVNW_REPOURL%" == "" (
+        SET DOWNLOAD_URL="%MVNW_REPOURL%/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+    )
+    if "%MVNW_VERBOSE%" == "true" (
+        echo Couldn't find %WRAPPER_JAR%, downloading it ...
+        echo Downloading from: %DOWNLOAD_URL%
+    )
+
+    powershell -Command "&{"^
+		"$webclient = new-object System.Net.WebClient;"^
+		"if (-not ([string]::IsNullOrEmpty('%MVNW_USERNAME%') -and [string]::IsNullOrEmpty('%MVNW_PASSWORD%'))) {"^
+		"$webclient.Credentials = new-object System.Net.NetworkCredential('%MVNW_USERNAME%', '%MVNW_PASSWORD%');"^
+		"}"^
+		"[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12; $webclient.DownloadFile('%DOWNLOAD_URL%', '%WRAPPER_JAR%')"^
+		"}"
+    if "%MVNW_VERBOSE%" == "true" (
+        echo Finished downloading %WRAPPER_JAR%
+    )
+)
+@REM End of extension
+
+@REM Provide a "standardized" way to retrieve the CLI args that will
+@REM work with both Windows and non-Windows executions.
+set MAVEN_CMD_LINE_ARGS=%*
+
+%MAVEN_JAVA_EXE% %JVM_CONFIG_MAVEN_PROPS% %MAVEN_OPTS% %MAVEN_DEBUG_OPTS% -classpath %WRAPPER_JAR% "-Dmaven.multiModuleProjectDirectory=%MAVEN_PROJECTBASEDIR%" %WRAPPER_LAUNCHER% %MAVEN_CONFIG% %*
+if ERRORLEVEL 1 goto error
+goto end
+
+:error
+set ERROR_CODE=1
+
+:end
+@endlocal & set ERROR_CODE=%ERROR_CODE%
+
+if not "%MAVEN_SKIP_RC%" == "" goto skipRcPost
+@REM check for post script, once with legacy .bat ending and once with .cmd ending
+if exist "%HOME%\mavenrc_post.bat" call "%HOME%\mavenrc_post.bat"
+if exist "%HOME%\mavenrc_post.cmd" call "%HOME%\mavenrc_post.cmd"
+:skipRcPost
+
+@REM pause the script if MAVEN_BATCH_PAUSE is set to 'on'
+if "%MAVEN_BATCH_PAUSE%" == "on" pause
+
+if "%MAVEN_TERMINATE_CMD%" == "on" exit %ERROR_CODE%
+
+exit /B %ERROR_CODE%

tapas-auction-house/pom.xml

@@ -0,0 +1,80 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>org.springframework.boot</groupId>
+		<artifactId>spring-boot-starter-parent</artifactId>
+		<version>2.5.3</version>
+		<relativePath/> <!-- lookup parent from repository -->
+	</parent>
+	<groupId>ch.unisg</groupId>
+	<artifactId>tapas-auction-house</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+	<name>tapas-auction-house</name>
+	<description>TAPAS Auction House</description>
+	<properties>
+		<java.version>11</java.version>
+	</properties>
+	<repositories>
+		<repository>
+			<id>Eclipse Paho Repo</id>
+			<url>https://repo.eclipse.org/content/repositories/paho-releases/</url>
+		</repository>
+	</repositories>
+	<dependencies>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-web</artifactId>
+		</dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-validation</artifactId>
+        </dependency>
+
+		<dependency>
+			<groupId>org.projectlombok</groupId>
+			<artifactId>lombok</artifactId>
+			<optional>true</optional>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-test</artifactId>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.eclipse.paho</groupId>
+			<artifactId>org.eclipse.paho.client.mqttv3</artifactId>
+			<version>1.2.0</version>
+		</dependency>
+        <dependency>
+            <groupId>javax.transaction</groupId>
+            <artifactId>javax.transaction-api</artifactId>
+            <version>1.2</version>
+        </dependency>
+        <dependency>
+            <groupId>javax.validation</groupId>
+            <artifactId>validation-api</artifactId>
+            <version>1.1.0.Final</version>
+        </dependency>
+    </dependencies>
+
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.springframework.boot</groupId>
+				<artifactId>spring-boot-maven-plugin</artifactId>
+				<configuration>
+					<excludes>
+						<exclude>
+							<groupId>org.projectlombok</groupId>
+							<artifactId>lombok</artifactId>
+						</exclude>
+					</excludes>
+				</configuration>
+			</plugin>
+		</plugins>
+	</build>
+
+</project>

tapas-auction-house/src/main/java/ch/unisg/tapas/TapasAuctionHouseApplication.java

@@ -0,0 +1,71 @@
+package ch.unisg.tapas;
+
+import ch.unisg.tapas.auctionhouse.adapter.common.clients.TapasMqttClient;
+import ch.unisg.tapas.auctionhouse.adapter.in.messaging.mqtt.AuctionEventsMqttDispatcher;
+import ch.unisg.tapas.auctionhouse.adapter.common.clients.WebSubSubscriber;
+import ch.unisg.tapas.common.AuctionHouseResourceDirectory;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.eclipse.paho.client.mqttv3.MqttException;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+import java.net.URI;
+import java.util.List;
+
+/**
+ * Main TAPAS Auction House application.
+ */
+@SpringBootApplication
+public class TapasAuctionHouseApplication {
+    private static final Logger LOGGER = LogManager.getLogger(TapasAuctionHouseApplication.class);
+
+    public static String RESOURCE_DIRECTORY = "https://api.interactions.ics.unisg.ch/auction-houses/";
+    public static String MQTT_BROKER = "tcp://broker.hivemq.com:1883";
+
+    public static void main(String[] args) {
+		SpringApplication tapasAuctioneerApp = new SpringApplication(TapasAuctionHouseApplication.class);
+
+		// We will use these bootstrap methods in Week 6:
+        // bootstrapMarketplaceWithWebSub();
+        // bootstrapMarketplaceWithMqtt();
+
+        tapasAuctioneerApp.run(args);
+	}
+
+    /**
+     * Discovers auction houses and subscribes to WebSub notifications
+     */
+	private static void bootstrapMarketplaceWithWebSub() {
+        List<String> auctionHouseEndpoints = discoverAuctionHouseEndpoints();
+        LOGGER.info("Found auction house endpoints: " + auctionHouseEndpoints);
+
+        WebSubSubscriber subscriber = new WebSubSubscriber();
+
+        for (String endpoint : auctionHouseEndpoints) {
+            subscriber.subscribeToAuctionHouseEndpoint(URI.create(endpoint));
+        }
+    }
+
+    /**
+     * Connects to an MQTT broker, presumably the one used by all TAPAS groups to communicate with
+     * one another
+     */
+    private static void bootstrapMarketplaceWithMqtt() {
+        try {
+            AuctionEventsMqttDispatcher dispatcher = new AuctionEventsMqttDispatcher();
+            TapasMqttClient client = TapasMqttClient.getInstance(MQTT_BROKER, dispatcher);
+            client.startReceivingMessages();
+        } catch (MqttException e) {
+            LOGGER.error(e.getMessage(), e);
+        }
+    }
+
+	private static List<String> discoverAuctionHouseEndpoints() {
+        AuctionHouseResourceDirectory rd = new AuctionHouseResourceDirectory(
+            URI.create(RESOURCE_DIRECTORY)
+        );
+
+	    return rd.retrieveAuctionHouseEndpoints();
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/common/clients/TapasMqttClient.java

@@ -0,0 +1,94 @@
+package ch.unisg.tapas.auctionhouse.adapter.common.clients;
+
+import ch.unisg.tapas.auctionhouse.adapter.in.messaging.mqtt.AuctionEventsMqttDispatcher;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.eclipse.paho.client.mqttv3.*;
+import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
+
+import java.nio.charset.StandardCharsets;
+import java.util.UUID;
+
+/**
+ * MQTT client for your TAPAS application. This class is defined as a singleton, but it does not have
+ * to be this way. This class is only provided as an example to help you bootstrap your project.
+ * You are welcomed to change this class as you see fit.
+ */
+public class TapasMqttClient {
+    private static final Logger LOGGER = LogManager.getLogger(TapasMqttClient.class);
+
+    private static TapasMqttClient tapasClient = null;
+
+    private MqttClient mqttClient;
+    private final String mqttClientId;
+    private final String brokerAddress;
+
+    private final MessageReceivedCallback messageReceivedCallback;
+
+    private final AuctionEventsMqttDispatcher dispatcher;
+
+    private TapasMqttClient(String brokerAddress, AuctionEventsMqttDispatcher dispatcher) {
+        this.mqttClientId = UUID.randomUUID().toString();
+        this.brokerAddress = brokerAddress;
+
+        this.messageReceivedCallback = new MessageReceivedCallback();
+
+        this.dispatcher = dispatcher;
+    }
+
+    public static synchronized TapasMqttClient getInstance(String brokerAddress,
+            AuctionEventsMqttDispatcher dispatcher) {
+
+        if (tapasClient == null) {
+            tapasClient = new TapasMqttClient(brokerAddress, dispatcher);
+        }
+
+        return tapasClient;
+    }
+
+    public void startReceivingMessages() throws MqttException {
+        mqttClient = new org.eclipse.paho.client.mqttv3.MqttClient(brokerAddress, mqttClientId, new MemoryPersistence());
+        mqttClient.connect();
+        mqttClient.setCallback(messageReceivedCallback);
+
+        subscribeToAllTopics();
+    }
+
+    public void stopReceivingMessages() throws MqttException {
+        mqttClient.disconnect();
+    }
+
+    private void subscribeToAllTopics() throws MqttException {
+        for (String topic : dispatcher.getAllTopics()) {
+            subscribeToTopic(topic);
+        }
+    }
+
+    private void subscribeToTopic(String topic) throws MqttException {
+        mqttClient.subscribe(topic);
+    }
+
+    private void publishMessage(String topic, String payload) throws MqttException {
+        MqttMessage message = new MqttMessage(payload.getBytes(StandardCharsets.UTF_8));
+        mqttClient.publish(topic, message);
+    }
+
+    private class MessageReceivedCallback implements MqttCallback {
+
+        @Override
+        public void connectionLost(Throwable cause) {  }
+
+        @Override
+        public void messageArrived(String topic, MqttMessage message) {
+            LOGGER.info("Received new MQTT message for topic " + topic + ": "
+                + new String(message.getPayload()));
+
+            if (topic != null && !topic.isEmpty()) {
+                dispatcher.dispatchEvent(topic, message);
+            }
+        }
+
+        @Override
+        public void deliveryComplete(IMqttDeliveryToken token) {  }
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/common/clients/WebSubSubscriber.java

@@ -0,0 +1,28 @@
+package ch.unisg.tapas.auctionhouse.adapter.common.clients;
+
+import java.net.URI;
+
+/**
+ * Subscribes to the WebSub hubs of auction houses discovered at run time. This class is instantiated
+ * from {@link ch.unisg.tapas.TapasAuctionHouseApplication} when boostraping the TAPAS marketplace
+ * via WebSub.
+ */
+public class WebSubSubscriber {
+
+    public void subscribeToAuctionHouseEndpoint(URI endpoint) {
+        // TODO Subscribe to the auction house endpoint via WebSub:
+        // 1. Send a request to the auction house in order to discover the WebSub hub to subscribe to.
+        // The request URI should depend on the design of the Auction House HTTP API.
+        // 2. Send a subscription request to the discovered WebSub hub to subscribe to events relevant
+        // for this auction house.
+        // 3. Handle the validation of intent from the WebSub hub (see WebSub protocol).
+        //
+        // Once the subscription is activated, the hub will send "fat pings" with content updates.
+        // The content received from the hub will depend primarily on the design of the Auction House
+        // HTTP API.
+        //
+        // For further details see:
+        // - W3C WebSub Recommendation: https://www.w3.org/TR/websub/
+        // - the implementation notes of the WebSub hub you are using to distribute events
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/common/formats/AuctionJsonRepresentation.java

@@ -0,0 +1,60 @@
+package ch.unisg.tapas.auctionhouse.adapter.common.formats;
+
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import lombok.Getter;
+import lombok.Setter;
+
+/**
+ * Used to expose a representation of the state of an auction through an interface. This class is
+ * only meant as a starting point when defining a uniform HTTP API for the Auction House: feel free
+ * to modify this class as you see fit!
+ */
+public class AuctionJsonRepresentation {
+    public static final String MEDIA_TYPE = "application/json";
+
+    @Getter @Setter
+    private String auctionId;
+
+    @Getter @Setter
+    private String auctionHouseUri;
+
+    @Getter @Setter
+    private String taskUri;
+
+    @Getter @Setter
+    private String taskType;
+
+    @Getter @Setter
+    private Integer deadline;
+
+    public AuctionJsonRepresentation() {  }
+
+    public AuctionJsonRepresentation(String auctionId, String auctionHouseUri, String taskUri,
+            String taskType, Integer deadline) {
+        this.auctionId = auctionId;
+        this.auctionHouseUri = auctionHouseUri;
+        this.taskUri = taskUri;
+        this.taskType = taskType;
+        this.deadline = deadline;
+    }
+
+    public AuctionJsonRepresentation(Auction auction) {
+        this.auctionId = auction.getAuctionId().getValue();
+        this.auctionHouseUri = auction.getAuctionHouseUri().getValue().toString();
+        this.taskUri = auction.getTaskUri().getValue().toString();
+        this.taskType = auction.getTaskType().getValue();
+        this.deadline = auction.getDeadline().getValue();
+    }
+
+    public static String serialize(Auction auction) throws JsonProcessingException {
+        AuctionJsonRepresentation representation = new AuctionJsonRepresentation(auction);
+
+        ObjectMapper mapper = new ObjectMapper();
+        mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
+
+        return mapper.writeValueAsString(representation);
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/in/messaging/http/ExecutorAddedEventListenerHttpAdapter.java

@@ -0,0 +1,35 @@
+package ch.unisg.tapas.auctionhouse.adapter.in.messaging.http;
+
+import ch.unisg.tapas.auctionhouse.application.handler.ExecutorAddedHandler;
+import ch.unisg.tapas.auctionhouse.application.port.in.ExecutorAddedEvent;
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+import ch.unisg.tapas.auctionhouse.domain.ExecutorRegistry;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+/*
+    THIS CLASS WILL BE PROVIDED ONLY AS A TEMPLATE; POINT OUT THE API NEEDS TO BE DEFINED
+*/
+
+@RestController
+public class ExecutorAddedEventListenerHttpAdapter {
+
+    @PostMapping(path = "/executors/{taskType}/{executorId}")
+    public ResponseEntity<String> handleExecutorAddedEvent(@PathVariable("taskType") String taskType,
+                                                         @PathVariable("executorId") String executorId) {
+
+        ExecutorAddedEvent executorAddedEvent = new ExecutorAddedEvent(
+            new ExecutorRegistry.ExecutorIdentifier(executorId),
+            new Auction.AuctionedTaskType(taskType)
+        );
+
+        ExecutorAddedHandler newExecutorHandler = new ExecutorAddedHandler();
+        newExecutorHandler.handleNewExecutorEvent(executorAddedEvent);
+
+        return new ResponseEntity<>(HttpStatus.NO_CONTENT);
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/in/messaging/http/ExecutorRemovedEventListenerHttpAdapter.java

@@ -0,0 +1,16 @@
+package ch.unisg.tapas.auctionhouse.adapter.in.messaging.http;
+
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RestController;
+
+/**
+ * Template for handling an executor removed event received via an HTTP request
+ */
+@RestController
+public class ExecutorRemovedEventListenerHttpAdapter {
+
+    // TODO: add annotations for request method, request URI, etc.
+    public void handleExecutorRemovedEvent(@PathVariable("executorId") String executorId) {
+        // TODO: implement logic
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/in/messaging/mqtt/AuctionEventMqttListener.java

@@ -0,0 +1,11 @@
+package ch.unisg.tapas.auctionhouse.adapter.in.messaging.mqtt;
+
+import org.eclipse.paho.client.mqttv3.MqttMessage;
+
+/**
+ * Abstract MQTT listener for auction-related events
+ */
+public abstract class AuctionEventMqttListener {
+
+    public abstract boolean handleEvent(MqttMessage message);
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/in/messaging/mqtt/AuctionEventsMqttDispatcher.java

@@ -0,0 +1,51 @@
+package ch.unisg.tapas.auctionhouse.adapter.in.messaging.mqtt;
+
+import org.eclipse.paho.client.mqttv3.*;
+
+import java.util.Hashtable;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * Dispatches MQTT messages for known topics to associated event listeners. Used in conjunction with
+ * {@link ch.unisg.tapas.auctionhouse.adapter.common.clients.TapasMqttClient}.
+ *
+ * This is where you would define MQTT topics and map them to event listeners (see
+ * {@link AuctionEventsMqttDispatcher#initRouter()}).
+ *
+ * This class is only provided as an example to help you bootstrap the project. You are welcomed to
+ * change this class as you see fit.
+ */
+public class AuctionEventsMqttDispatcher {
+    private final Map<String, AuctionEventMqttListener> router;
+
+    public AuctionEventsMqttDispatcher() {
+        this.router = new Hashtable<>();
+        initRouter();
+    }
+
+    // TODO: Register here your topics and event listener adapters
+    private void initRouter() {
+        router.put("ch/unisg/tapas-group-tutors/executors", new ExecutorAddedEventListenerMqttAdapter());
+    }
+
+    /**
+     * Returns all topics registered with this dispatcher.
+     *
+     * @return the set of registered topics
+     */
+    public Set<String> getAllTopics() {
+        return router.keySet();
+    }
+
+    /**
+     * Dispatches an event received via MQTT for a given topic.
+     *
+     * @param topic the topic for which the MQTT message was received
+     * @param message the received MQTT message
+     */
+    public void dispatchEvent(String topic, MqttMessage message) {
+        AuctionEventMqttListener listener = router.get(topic);
+        listener.handleEvent(message);
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/in/messaging/mqtt/ExecutorAddedEventListenerMqttAdapter.java

@@ -0,0 +1,46 @@
+package ch.unisg.tapas.auctionhouse.adapter.in.messaging.mqtt;
+
+import ch.unisg.tapas.auctionhouse.application.handler.ExecutorAddedHandler;
+import ch.unisg.tapas.auctionhouse.application.port.in.ExecutorAddedEvent;
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+import ch.unisg.tapas.auctionhouse.domain.ExecutorRegistry;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.eclipse.paho.client.mqttv3.MqttMessage;
+
+/**
+ * Listener that handles events when an executor was added to this TAPAS application.
+ *
+ * This class is only provided as an example to help you bootstrap the project.
+ */
+public class ExecutorAddedEventListenerMqttAdapter extends AuctionEventMqttListener {
+
+    @Override
+    public boolean handleEvent(MqttMessage message) {
+        String payload = new String(message.getPayload());
+
+        try {
+            // Note: this messge representation is provided only as an example. You should use a
+            // representation that makes sense in the context of your application.
+            JsonNode data = new ObjectMapper().readTree(payload);
+
+            String taskType = data.get("taskType").asText();
+            String executorId = data.get("executorId").asText();
+
+            ExecutorAddedEvent executorAddedEvent = new ExecutorAddedEvent(
+                new ExecutorRegistry.ExecutorIdentifier(executorId),
+                new Auction.AuctionedTaskType(taskType)
+            );
+
+            ExecutorAddedHandler newExecutorHandler = new ExecutorAddedHandler();
+            newExecutorHandler.handleNewExecutorEvent(executorAddedEvent);
+        } catch (JsonProcessingException | NullPointerException e) {
+            // TODO: refactor logging
+            e.printStackTrace();
+            return false;
+        }
+
+        return true;
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/in/messaging/websub/AuctionStartedEventListenerWebSubAdapter.java

@@ -0,0 +1,18 @@
+package ch.unisg.tapas.auctionhouse.adapter.in.messaging.websub;
+
+import ch.unisg.tapas.auctionhouse.application.handler.AuctionStartedHandler;
+import org.springframework.web.bind.annotation.*;
+
+/**
+ * This class is a template for handling auction started events received via WebSub
+ */
+@RestController
+public class AuctionStartedEventListenerWebSubAdapter {
+    private final AuctionStartedHandler auctionStartedHandler;
+
+    public AuctionStartedEventListenerWebSubAdapter(AuctionStartedHandler auctionStartedHandler) {
+        this.auctionStartedHandler = auctionStartedHandler;
+    }
+
+    //TODO
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/in/web/LaunchAuctionWebController.java

@@ -0,0 +1,72 @@
+package ch.unisg.tapas.auctionhouse.adapter.in.web;
+
+import ch.unisg.tapas.auctionhouse.adapter.common.formats.AuctionJsonRepresentation;
+import ch.unisg.tapas.auctionhouse.application.port.in.LaunchAuctionCommand;
+import ch.unisg.tapas.auctionhouse.application.port.in.LaunchAuctionUseCase;
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.server.ResponseStatusException;
+
+import java.net.URI;
+
+/**
+ * Controller that handles HTTP requests for launching auctions. This controller implements the
+ * {@link LaunchAuctionUseCase} use case using the {@link LaunchAuctionCommand}.
+ */
+@RestController
+public class LaunchAuctionWebController {
+    private final LaunchAuctionUseCase launchAuctionUseCase;
+
+    /**
+     * Constructs the controller.
+     *
+     * @param launchAuctionUseCase an implementation of the launch auction use case
+     */
+    public LaunchAuctionWebController(LaunchAuctionUseCase launchAuctionUseCase) {
+        this.launchAuctionUseCase = launchAuctionUseCase;
+    }
+
+    /**
+     * Handles HTTP POST requests for launching auctions. Note: you are free to modify this handler
+     * as you see fit to reflect the discussions for the uniform HTTP API for the auction house.
+     * You should also ensure that this handler has the exact behavior you would expect from the
+     * defined uniform HTTP API (status codes, returned payload, HTTP headers, etc.)
+     *
+     * @param payload a representation of the auction to be launched
+     * @return
+     */
+    @PostMapping(path = "/auctions/", consumes = AuctionJsonRepresentation.MEDIA_TYPE)
+    public ResponseEntity<String> launchAuction(@RequestBody AuctionJsonRepresentation payload) {
+        Auction.AuctionDeadline deadline = (payload.getDeadline() == null) ?
+            null : new Auction.AuctionDeadline(payload.getDeadline());
+
+        LaunchAuctionCommand command = new LaunchAuctionCommand(
+            new Auction.AuctionedTaskUri(URI.create(payload.getTaskUri())),
+            new Auction.AuctionedTaskType(payload.getTaskType()),
+            deadline
+        );
+
+        // This command returns the created auction. We need the created auction to be able to
+        // include a representation of it in the HTTP response.
+        Auction auction = launchAuctionUseCase.launchAuction(command);
+
+        try {
+            AuctionJsonRepresentation representation = new AuctionJsonRepresentation(auction);
+            String auctionJson = AuctionJsonRepresentation.serialize(auction);
+
+            HttpHeaders responseHeaders = new HttpHeaders();
+            responseHeaders.add(HttpHeaders.CONTENT_TYPE, AuctionJsonRepresentation.MEDIA_TYPE);
+
+            // Return a 201 Created status code and a representation of the created auction
+            return new ResponseEntity<>(auctionJson, responseHeaders, HttpStatus.CREATED);
+        } catch (JsonProcessingException e) {
+            throw new ResponseStatusException(HttpStatus.INTERNAL_SERVER_ERROR);
+        }
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/in/web/RetrieveOpenAuctionsWebController.java

@@ -0,0 +1,62 @@
+package ch.unisg.tapas.auctionhouse.adapter.in.web;
+
+import ch.unisg.tapas.auctionhouse.adapter.common.formats.AuctionJsonRepresentation;
+import ch.unisg.tapas.auctionhouse.application.port.in.RetrieveOpenAuctionsQuery;
+import ch.unisg.tapas.auctionhouse.application.port.in.RetrieveOpenAuctionsUseCase;
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ArrayNode;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.Collection;
+
+/**
+ * Controller that handles HTTP requests for retrieving auctions hosted by this auction house that
+ * are open for bids. This controller implements the {@link RetrieveOpenAuctionsUseCase} use case
+ * using the {@link RetrieveOpenAuctionsQuery}.
+ */
+@RestController
+public class RetrieveOpenAuctionsWebController {
+    private final RetrieveOpenAuctionsUseCase retrieveAuctionListUseCase;
+
+    public RetrieveOpenAuctionsWebController(RetrieveOpenAuctionsUseCase retrieveAuctionListUseCase) {
+        this.retrieveAuctionListUseCase = retrieveAuctionListUseCase;
+    }
+
+    /**
+     * Handles HTTP GET requests to retrieve the auctions that are open. Note: you are free to modify
+     * this handler as you see fit to reflect the discussions for the uniform HTTP API for the
+     * auction house. You should also ensure that this handler has the exact behavior you would expect
+     * from the defined uniform HTTP API (status codes, returned payload, HTTP headers, etc.).
+     *
+     * @return a representation of a collection with the auctions that are open for bids
+     */
+    @GetMapping(path = "/auctions/")
+    public ResponseEntity<String> retrieveOpenAuctions() {
+        Collection<Auction> auctions =
+            retrieveAuctionListUseCase.retrieveAuctions(new RetrieveOpenAuctionsQuery());
+
+        ObjectMapper mapper = new ObjectMapper();
+        ArrayNode array = mapper.createArrayNode();
+
+        for (Auction auction : auctions) {
+            AuctionJsonRepresentation representation = new AuctionJsonRepresentation(auction);
+            JsonNode node = mapper.valueToTree(representation);
+            array.add(node);
+        }
+
+        HttpHeaders responseHeaders = new HttpHeaders();
+        responseHeaders.add(HttpHeaders.CONTENT_TYPE, "application/json");
+
+        // TODO before providing to students: remove hub links
+        responseHeaders.add(HttpHeaders.LINK, "<https://pubsubhubbub.appspot.com/>; rel=\"hub\"");
+        responseHeaders.add(HttpHeaders.LINK, "<http://example.org/auctions/>; rel=\"self\"");
+
+        return new ResponseEntity<>(array.toString(), responseHeaders, HttpStatus.OK);
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/out/messaging/websub/PublishAuctionStartedEventWebSubAdapter.java

@@ -0,0 +1,37 @@
+package ch.unisg.tapas.auctionhouse.adapter.out.messaging.websub;
+
+import ch.unisg.tapas.auctionhouse.application.port.out.AuctionStartedEventPort;
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+import ch.unisg.tapas.auctionhouse.domain.AuctionStartedEvent;
+import ch.unisg.tapas.common.ConfigProperties;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Primary;
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Component;
+
+import java.io.IOException;
+import java.net.URLEncoder;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.nio.charset.StandardCharsets;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * This class is a template for publishing auction started events via WebSub.
+ */
+@Component
+@Primary
+public class PublishAuctionStartedEventWebSubAdapter implements AuctionStartedEventPort {
+    // You can use this object to retrieve properties from application.properties, e.g. the
+    // WebSub hub publish endpoint, etc.
+    @Autowired
+    private ConfigProperties config;
+
+    @Override
+    public void publishAuctionStartedEvent(AuctionStartedEvent event) {
+        // TODO
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/out/web/AuctionWonEventHttpAdapter.java

@@ -0,0 +1,20 @@
+package ch.unisg.tapas.auctionhouse.adapter.out.web;
+
+import ch.unisg.tapas.auctionhouse.application.port.out.AuctionWonEventPort;
+import ch.unisg.tapas.auctionhouse.domain.AuctionWonEvent;
+import org.springframework.context.annotation.Primary;
+import org.springframework.stereotype.Component;
+
+/**
+ * This class is a template for sending auction won events via HTTP. This class was created here only
+ * as a placeholder, it is up to you to decide how such events should be sent (e.g., via HTTP,
+ * WebSub, etc.).
+ */
+@Component
+@Primary
+public class AuctionWonEventHttpAdapter implements AuctionWonEventPort {
+    @Override
+    public void publishAuctionWonEvent(AuctionWonEvent event) {
+
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/adapter/out/web/PlaceBidForAuctionCommandHttpAdapter.java

@@ -0,0 +1,19 @@
+package ch.unisg.tapas.auctionhouse.adapter.out.web;
+
+import ch.unisg.tapas.auctionhouse.application.port.out.PlaceBidForAuctionCommand;
+import ch.unisg.tapas.auctionhouse.application.port.out.PlaceBidForAuctionCommandPort;
+import org.springframework.context.annotation.Primary;
+import org.springframework.stereotype.Component;
+
+/**
+ * This class is a tempalte for implementing a place bid for auction command via HTTP.
+ */
+@Component
+@Primary
+public class PlaceBidForAuctionCommandHttpAdapter implements PlaceBidForAuctionCommandPort {
+
+    @Override
+    public void placeBid(PlaceBidForAuctionCommand command) {
+        // TODO
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/handler/AuctionStartedHandler.java

@@ -0,0 +1,59 @@
+package ch.unisg.tapas.auctionhouse.application.handler;
+
+import ch.unisg.tapas.auctionhouse.application.port.in.AuctionStartedEvent;
+import ch.unisg.tapas.auctionhouse.application.port.in.AuctionStartedEventHandler;
+import ch.unisg.tapas.auctionhouse.application.port.out.PlaceBidForAuctionCommand;
+import ch.unisg.tapas.auctionhouse.application.port.out.PlaceBidForAuctionCommandPort;
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+import ch.unisg.tapas.auctionhouse.domain.Bid;
+import ch.unisg.tapas.auctionhouse.domain.ExecutorRegistry;
+import ch.unisg.tapas.common.ConfigProperties;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Component;
+
+/**
+ * Handler for auction started events. This handler will automatically bid in any auction for a
+ * task of known type, i.e. a task for which the auction house knows an executor is available.
+ */
+@Component
+public class AuctionStartedHandler implements AuctionStartedEventHandler {
+    private static final Logger LOGGER = LogManager.getLogger(AuctionStartedHandler.class);
+
+    @Autowired
+    private ConfigProperties config;
+
+    @Autowired
+    private PlaceBidForAuctionCommandPort placeBidForAuctionCommandPort;
+
+    /**
+     * Handles an auction started event and bids in all auctions for tasks of known types.
+     *
+     * @param auctionStartedEvent the auction started domain event
+     * @return true unless a runtime exception occurs
+     */
+    @Override
+    public boolean handleAuctionStartedEvent(AuctionStartedEvent auctionStartedEvent) {
+        Auction auction = auctionStartedEvent.getAuction();
+
+        if (ExecutorRegistry.getInstance().containsTaskType(auction.getTaskType())) {
+            LOGGER.info("Placing bid for task " + auction.getTaskUri() + " of type "
+                + auction.getTaskType() + " in auction " + auction.getAuctionId()
+                + " from auction house " + auction.getAuctionHouseUri().getValue().toString());
+
+            Bid bid = new Bid(auction.getAuctionId(),
+                new Bid.BidderName(config.getGroupName()),
+                new Bid.BidderAuctionHouseUri(config.getAuctionHouseUri()),
+                new Bid.BidderTaskListUri(config.getTaskListUri())
+            );
+
+            PlaceBidForAuctionCommand command = new PlaceBidForAuctionCommand(auction, bid);
+            placeBidForAuctionCommandPort.placeBid(command);
+        } else {
+            LOGGER.info("Cannot execute this task type: " + auction.getTaskType().getValue());
+        }
+
+        return true;
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/handler/ExecutorAddedHandler.java

@@ -0,0 +1,16 @@
+package ch.unisg.tapas.auctionhouse.application.handler;
+
+import ch.unisg.tapas.auctionhouse.application.port.in.ExecutorAddedEvent;
+import ch.unisg.tapas.auctionhouse.application.port.in.ExecutorAddedEventHandler;
+import ch.unisg.tapas.auctionhouse.domain.ExecutorRegistry;
+import org.springframework.stereotype.Component;
+
+@Component
+public class ExecutorAddedHandler implements ExecutorAddedEventHandler {
+
+    @Override
+    public boolean handleNewExecutorEvent(ExecutorAddedEvent executorAddedEvent) {
+        return ExecutorRegistry.getInstance().addExecutor(executorAddedEvent.getTaskType(),
+            executorAddedEvent.getExecutorId());
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/handler/ExecutorRemovedHandler.java

@@ -0,0 +1,19 @@
+package ch.unisg.tapas.auctionhouse.application.handler;
+
+import ch.unisg.tapas.auctionhouse.application.port.in.ExecutorRemovedEvent;
+import ch.unisg.tapas.auctionhouse.application.port.in.ExecutorRemovedEventHandler;
+import ch.unisg.tapas.auctionhouse.domain.ExecutorRegistry;
+import org.springframework.stereotype.Component;
+
+/**
+ * Handler for executor removed events. It removes the executor from this auction house's executor
+ * registry.
+ */
+@Component
+public class ExecutorRemovedHandler implements ExecutorRemovedEventHandler {
+
+    @Override
+    public boolean handleExecutorRemovedEvent(ExecutorRemovedEvent executorRemovedEvent) {
+        return ExecutorRegistry.getInstance().removeExecutor(executorRemovedEvent.getExecutorId());
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/AuctionStartedEvent.java

@@ -0,0 +1,21 @@
+package ch.unisg.tapas.auctionhouse.application.port.in;
+
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+import ch.unisg.tapas.common.SelfValidating;
+import lombok.Value;
+
+import javax.validation.constraints.NotNull;
+
+/**
+ * Event that notifies this auction house that an auction was started by another auction house.
+ */
+@Value
+public class AuctionStartedEvent extends SelfValidating<AuctionStartedEvent> {
+    @NotNull
+    private final Auction auction;
+
+    public AuctionStartedEvent(Auction auction) {
+        this.auction = auction;
+        this.validateSelf();
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/AuctionStartedEventHandler.java

@@ -0,0 +1,6 @@
+package ch.unisg.tapas.auctionhouse.application.port.in;
+
+public interface AuctionStartedEventHandler {
+
+    boolean handleAuctionStartedEvent(AuctionStartedEvent auctionStartedEvent);
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/ExecutorAddedEvent.java

@@ -0,0 +1,32 @@
+package ch.unisg.tapas.auctionhouse.application.port.in;
+
+import ch.unisg.tapas.auctionhouse.domain.Auction.AuctionedTaskType;
+import ch.unisg.tapas.auctionhouse.domain.ExecutorRegistry.ExecutorIdentifier;
+import ch.unisg.tapas.common.SelfValidating;
+import lombok.Value;
+
+import javax.validation.constraints.NotNull;
+
+/**
+ * Event that notifies the auction house that an executor has been added to this TAPAS application.
+ */
+@Value
+public class ExecutorAddedEvent extends SelfValidating<ExecutorAddedEvent> {
+    @NotNull
+    private final ExecutorIdentifier executorId;
+
+    @NotNull
+    private final AuctionedTaskType taskType;
+
+    /**
+     * Constructs an executor added event.
+     *
+     * @param executorId the identifier of the executor that was added to this TAPAS application
+     */
+    public ExecutorAddedEvent(ExecutorIdentifier executorId, AuctionedTaskType taskType) {
+        this.executorId = executorId;
+        this.taskType = taskType;
+
+        this.validateSelf();
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/ExecutorAddedEventHandler.java

@@ -0,0 +1,6 @@
+package ch.unisg.tapas.auctionhouse.application.port.in;
+
+public interface ExecutorAddedEventHandler {
+
+    boolean handleNewExecutorEvent(ExecutorAddedEvent executorAddedEvent);
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/ExecutorRemovedEvent.java

@@ -0,0 +1,26 @@
+package ch.unisg.tapas.auctionhouse.application.port.in;
+
+import ch.unisg.tapas.auctionhouse.domain.ExecutorRegistry.ExecutorIdentifier;
+import ch.unisg.tapas.common.SelfValidating;
+import lombok.Value;
+
+import javax.validation.constraints.NotNull;
+
+/**
+ * Event that notifies the auction house that an executor has been removed from this TAPAS application.
+ */
+@Value
+public class ExecutorRemovedEvent extends SelfValidating<ExecutorRemovedEvent> {
+    @NotNull
+    private final ExecutorIdentifier executorId;
+
+    /**
+     * Constructs an executor removed event.
+     *
+     * @param executorId the identifier of the executor that was removed from this TAPAS application
+     */
+    public ExecutorRemovedEvent(ExecutorIdentifier executorId) {
+        this.executorId = executorId;
+        this.validateSelf();
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/ExecutorRemovedEventHandler.java

@@ -0,0 +1,6 @@
+package ch.unisg.tapas.auctionhouse.application.port.in;
+
+public interface ExecutorRemovedEventHandler {
+
+    boolean handleExecutorRemovedEvent(ExecutorRemovedEvent executorRemovedEvent);
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/LaunchAuctionCommand.java

@@ -0,0 +1,37 @@
+package ch.unisg.tapas.auctionhouse.application.port.in;
+
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+import ch.unisg.tapas.common.SelfValidating;
+import lombok.Value;
+
+import javax.validation.constraints.NotNull;
+
+/**
+ * Command for launching an auction in this auction house.
+ */
+@Value
+public class LaunchAuctionCommand extends SelfValidating<LaunchAuctionCommand> {
+    @NotNull
+    private final Auction.AuctionedTaskUri taskUri;
+
+    @NotNull
+    private final Auction.AuctionedTaskType taskType;
+
+    private final Auction.AuctionDeadline deadline;
+
+    /**
+     * Constructs the launch action command.
+     *
+     * @param taskUri the URI of the auctioned task
+     * @param taskType the type of the auctioned task
+     * @param deadline the deadline by which the auction should receive bids (can be null if none)
+     */
+    public LaunchAuctionCommand(Auction.AuctionedTaskUri taskUri, Auction.AuctionedTaskType taskType,
+                                Auction.AuctionDeadline deadline) {
+        this.taskUri = taskUri;
+        this.taskType = taskType;
+        this.deadline = deadline;
+
+        this.validateSelf();
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/LaunchAuctionUseCase.java

@@ -0,0 +1,8 @@
+package ch.unisg.tapas.auctionhouse.application.port.in;
+
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+
+public interface LaunchAuctionUseCase {
+
+    Auction launchAuction(LaunchAuctionCommand command);
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/RetrieveOpenAuctionsQuery.java

@@ -0,0 +1,7 @@
+package ch.unisg.tapas.auctionhouse.application.port.in;
+
+/**
+ * Query used to retrieve open auctions. Although this query is empty, we model it to convey the
+ * domain semantics and to reduce coupling.
+ */
+public class RetrieveOpenAuctionsQuery {  }

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/in/RetrieveOpenAuctionsUseCase.java

@@ -0,0 +1,10 @@
+package ch.unisg.tapas.auctionhouse.application.port.in;
+
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+
+import java.util.Collection;
+
+public interface RetrieveOpenAuctionsUseCase {
+
+    Collection<Auction> retrieveAuctions(RetrieveOpenAuctionsQuery query);
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/out/AuctionStartedEventPort.java

@@ -0,0 +1,11 @@
+package ch.unisg.tapas.auctionhouse.application.port.out;
+
+import ch.unisg.tapas.auctionhouse.domain.AuctionStartedEvent;
+
+/**
+ * Port for sending out auction started events
+ */
+public interface AuctionStartedEventPort {
+
+    void publishAuctionStartedEvent(AuctionStartedEvent event);
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/out/AuctionWonEventPort.java

@@ -0,0 +1,11 @@
+package ch.unisg.tapas.auctionhouse.application.port.out;
+
+import ch.unisg.tapas.auctionhouse.domain.AuctionWonEvent;
+
+/**
+ * Port for sending out auction won events
+ */
+public interface AuctionWonEventPort {
+
+    void publishAuctionWonEvent(AuctionWonEvent event);
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/out/PlaceBidForAuctionCommand.java

@@ -0,0 +1,25 @@
+package ch.unisg.tapas.auctionhouse.application.port.out;
+
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+import ch.unisg.tapas.auctionhouse.domain.Bid;
+import ch.unisg.tapas.common.SelfValidating;
+import lombok.Value;
+
+import javax.validation.constraints.NotNull;
+
+/**
+ * Command to place a bid for a given auction.
+ */
+@Value
+public class PlaceBidForAuctionCommand extends SelfValidating<PlaceBidForAuctionCommand> {
+    @NotNull
+    private final Auction auction;
+    @NotNull
+    private final Bid bid;
+
+    public PlaceBidForAuctionCommand(Auction auction, Bid bid) {
+        this.auction = auction;
+        this.bid = bid;
+        this.validateSelf();
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/port/out/PlaceBidForAuctionCommandPort.java

@@ -0,0 +1,6 @@
+package ch.unisg.tapas.auctionhouse.application.port.out;
+
+public interface PlaceBidForAuctionCommandPort {
+
+    void placeBid(PlaceBidForAuctionCommand command);
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/service/RetrieveOpenAuctionsService.java

@@ -0,0 +1,22 @@
+package ch.unisg.tapas.auctionhouse.application.service;
+
+import ch.unisg.tapas.auctionhouse.application.port.in.RetrieveOpenAuctionsQuery;
+import ch.unisg.tapas.auctionhouse.application.port.in.RetrieveOpenAuctionsUseCase;
+import ch.unisg.tapas.auctionhouse.domain.Auction;
+import ch.unisg.tapas.auctionhouse.domain.AuctionRegistry;
+import org.springframework.stereotype.Component;
+
+import java.util.Collection;
+
+/**
+ * Service that implements {@link RetrieveOpenAuctionsUseCase} to retrieve all auctions in this auction
+ * house that are open for bids.
+ */
+@Component
+public class RetrieveOpenAuctionsService implements RetrieveOpenAuctionsUseCase {
+
+    @Override
+    public Collection<Auction> retrieveAuctions(RetrieveOpenAuctionsQuery query) {
+        return AuctionRegistry.getInstance().getOpenAuctions();
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/application/service/StartAuctionService.java

@@ -0,0 +1,113 @@
+package ch.unisg.tapas.auctionhouse.application.service;
+
+import ch.unisg.tapas.auctionhouse.application.port.in.LaunchAuctionCommand;
+import ch.unisg.tapas.auctionhouse.application.port.in.LaunchAuctionUseCase;
+import ch.unisg.tapas.auctionhouse.application.port.out.AuctionWonEventPort;
+import ch.unisg.tapas.auctionhouse.application.port.out.AuctionStartedEventPort;
+import ch.unisg.tapas.auctionhouse.domain.*;
+import ch.unisg.tapas.common.ConfigProperties;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Component;
+
+import java.util.Optional;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Service that implements the {@link LaunchAuctionUseCase} to start an auction. If a deadline is
+ * specified for the auction, the service automatically closes the auction at the deadline. If a
+ * deadline is not specified, the service closes the auction after 10s by default.
+ */
+@Component
+public class StartAuctionService implements LaunchAuctionUseCase {
+    private static final Logger LOGGER = LogManager.getLogger(StartAuctionService.class);
+
+    private final static int DEFAULT_AUCTION_DEADLINE_MILLIS = 10000;
+
+    // Event port used to publish an auction started event
+    private final AuctionStartedEventPort auctionStartedEventPort;
+    // Event port used to publish an auction won event
+    private final AuctionWonEventPort auctionWonEventPort;
+
+    private final ScheduledExecutorService service;
+    private final AuctionRegistry auctions;
+
+    @Autowired
+    private ConfigProperties config;
+
+    public StartAuctionService(AuctionStartedEventPort auctionStartedEventPort,
+                               AuctionWonEventPort auctionWonEventPort) {
+        this.auctionStartedEventPort = auctionStartedEventPort;
+        this.auctionWonEventPort = auctionWonEventPort;
+        this.auctions = AuctionRegistry.getInstance();
+        this.service = Executors.newScheduledThreadPool(1);
+    }
+
+    /**
+     * Launches an auction.
+     *
+     * @param command the domain command used to launch the auction (see {@link LaunchAuctionCommand})
+     * @return the launched auction
+     */
+    @Override
+    public Auction launchAuction(LaunchAuctionCommand command) {
+        Auction.AuctionDeadline deadline = (command.getDeadline() == null) ?
+            new Auction.AuctionDeadline(DEFAULT_AUCTION_DEADLINE_MILLIS) : command.getDeadline();
+
+        // Create a new auction and add it to the auction registry
+        Auction auction = new Auction(new Auction.AuctionHouseUri(config.getAuctionHouseUri()),
+            command.getTaskUri(), command.getTaskType(), deadline);
+        auctions.addAuction(auction);
+
+        // Schedule the closing of the auction at the deadline
+        service.schedule(new CloseAuctionTask(auction.getAuctionId()), deadline.getValue(),
+            TimeUnit.MILLISECONDS);
+
+        // Publish an auction started event
+        AuctionStartedEvent auctionStartedEvent = new AuctionStartedEvent(auction);
+        auctionStartedEventPort.publishAuctionStartedEvent(auctionStartedEvent);
+
+        return auction;
+    }
+
+    /**
+     * This task closes the auction at the deadline and selects a winner if any bids were placed. It
+     * also sends out associated events and commands.
+     */
+    private class CloseAuctionTask implements Runnable {
+        Auction.AuctionId auctionId;
+
+        public CloseAuctionTask(Auction.AuctionId auctionId) {
+            this.auctionId = auctionId;
+        }
+
+        @Override
+        public void run() {
+            Optional<Auction> auctionOpt = auctions.getAuctionById(auctionId);
+
+            if (auctionOpt.isPresent()) {
+                Auction auction = auctionOpt.get();
+                Optional<Bid> bid = auction.selectBid();
+
+                // Close the auction
+                auction.close();
+
+                if (bid.isPresent()) {
+                    // Notify the bidder
+                    Bid.BidderName bidderName = bid.get().getBidderName();
+                    LOGGER.info("Auction #" + auction.getAuctionId().getValue() + " for task "
+                            + auction.getTaskUri().getValue() + " won by " + bidderName.getValue());
+
+                    // Send an auction won event for the winning bid
+                    auctionWonEventPort.publishAuctionWonEvent(new AuctionWonEvent(bid.get()));
+                } else {
+                    LOGGER.info("Auction #" + auction.getAuctionId().getValue() + " ended with no bids for task "
+                            + auction.getTaskUri().getValue());
+                }
+            }
+        }
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/domain/Auction.java

@@ -0,0 +1,171 @@
+package ch.unisg.tapas.auctionhouse.domain;
+
+import lombok.Getter;
+import lombok.Value;
+
+import java.net.URI;
+import java.util.*;
+
+/**
+ * Domain entity that models an auction.
+ */
+public class Auction {
+    // Auctions have two possible states:
+    // - open: waiting for bids
+    // - closed: the auction deadline has expired, there may or may not be a winning bid
+    public enum Status {
+        OPEN, CLOSED
+    }
+
+    // One way to generate auction identifiers is incremental starting from 1. This makes identifiers
+    // predictable, which can help with debugging when multiple parties are interacting, but it also
+    // means that auction identifiers are not universally unique unless they are part of a URI.
+    // An alternative would be to use UUIDs (see constructor).
+    private static long AUCTION_COUNTER = 1;
+
+    @Getter
+    private AuctionId auctionId;
+
+    @Getter
+    private AuctionStatus auctionStatus;
+
+    // URI that identifies the auction house that started this auction. Given a uniform, standard
+    // HTTP API for auction houses, this URI can then be used as a base URI for interacting with
+    // the identified auction house.
+    @Getter
+    private final AuctionHouseUri auctionHouseUri;
+
+    // URI that identifies the task for which the auction was launched. URIs are uniform identifiers
+    // and can be referenced independent of context: because we have defined a uniform HTTP API for
+    // TAPAS-Tasks, we can dereference this URI to retrieve a complete representation of the
+    // auctioned task.
+    @Getter
+    private final AuctionedTaskUri taskUri;
+
+    // The type of the task being auctioned. We could also retrieve the task type by dereferencing
+    // the task's URI, but given that the bidding is defined primarily based on task types, knowing
+    // the task type avoids an additional HTTP request.
+    @Getter
+    private final AuctionedTaskType taskType;
+
+    // The deadline by which bids can be placed. Once the deadline expires, the auction is closed.
+    @Getter
+    private final AuctionDeadline deadline;
+
+    // Available bids.
+    @Getter
+    private final List<Bid> bids;
+
+    /**
+     * Constructs an auction.
+     *
+     * @param auctionHouseUri the URI of the auction hause that started the auction
+     * @param taskUri the URI of the task being auctioned
+     * @param taskType the type of the task being auctioned
+     * @param deadline the deadline by which the auction is open for bids
+     */
+    public Auction(AuctionHouseUri auctionHouseUri, AuctionedTaskUri taskUri,
+                   AuctionedTaskType taskType, AuctionDeadline deadline) {
+        // Generates an incremental identifier
+        this.auctionId = new AuctionId("" + AUCTION_COUNTER ++);
+        // As an alternative, we could also generate an UUID
+        // this.auctionId = new AuctionId(UUID.randomUUID().toString());
+
+        this.auctionStatus = new AuctionStatus(Status.OPEN);
+
+        this.auctionHouseUri = auctionHouseUri;
+        this.taskUri = taskUri;
+        this.taskType = taskType;
+
+        this.deadline = deadline;
+        this.bids = new ArrayList<>();
+    }
+
+    /**
+     * Constructs an auction.
+     *
+     * @param auctionId the identifier of the auction
+     * @param auctionHouseUri the URI of the auction hause that started the auction
+     * @param taskUri the URI of the task being auctioned
+     * @param taskType the type of the task being auctioned
+     * @param deadline the deadline by which the auction is open for bids
+     */
+    public Auction(AuctionId auctionId, AuctionHouseUri auctionHouseUri, AuctionedTaskUri taskUri,
+            AuctionedTaskType taskType, AuctionDeadline deadline) {
+        this(auctionHouseUri, taskUri, taskType, deadline);
+        this.auctionId = auctionId;
+    }
+
+    /**
+     * Places a bid for this auction.
+     *
+     * @param bid the bid
+     */
+    public void addBid(Bid bid) {
+        bids.add(bid);
+    }
+
+    /**
+     * Selects a bid randomly from the bids available for this auction.
+     *
+     * @return a winning bid or Optional.empty if no bid was made in this auction.
+     */
+    public Optional<Bid> selectBid() {
+        if (bids.isEmpty()) {
+            return Optional.empty();
+        }
+
+        int index = new Random().nextInt(bids.size());
+        return Optional.of(bids.get(index));
+    }
+
+    /**
+     * Checks if the auction is open for bids.
+     *
+     * @return true if open for bids, false if the auction is closed
+     */
+    public boolean isOpen() {
+        return auctionStatus.getValue() == Status.OPEN;
+    }
+
+    /**
+     * Closes the auction. Called by the StartAuctionService after the auction deadline has expired.
+     */
+    public void close() {
+        auctionStatus = new AuctionStatus(Status.CLOSED);
+    }
+
+    /*
+     * Definitions of Value Objects
+     */
+
+    @Value
+    public static class AuctionId {
+        String value;
+    }
+
+    @Value
+    public static class AuctionStatus {
+        Status value;
+    }
+
+    @Value
+    public static class AuctionHouseUri {
+        URI value;
+    }
+
+    @Value
+    public static class AuctionedTaskUri {
+        URI value;
+    }
+
+    @Value
+    public static class AuctionedTaskType {
+        String value;
+    }
+
+    @Value
+    public static class AuctionDeadline {
+        int value;
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/domain/AuctionRegistry.java

@@ -0,0 +1,105 @@
+package ch.unisg.tapas.auctionhouse.domain;
+
+import java.util.Collection;
+import java.util.Hashtable;
+import java.util.Map;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+/**
+ * Registry that keeps an in-memory history of auctions (both open for bids and closed). This class
+ * is a singleton. See also {@link Auction}.
+ */
+public class AuctionRegistry {
+    private static AuctionRegistry registry;
+
+    private final Map<Auction.AuctionId, Auction> auctions;
+
+    private AuctionRegistry() {
+        this.auctions = new Hashtable<>();
+    }
+
+    /**
+     * Retrieves a reference to the auction registry.
+     *
+     * @return the auction registry
+     */
+    public static synchronized AuctionRegistry getInstance() {
+        if (registry == null) {
+            registry = new AuctionRegistry();
+        }
+
+        return registry;
+    }
+
+    /**
+     * Adds a new auction to the registry
+     * @param auction the new auction
+     */
+    public void addAuction(Auction auction) {
+        auctions.put(auction.getAuctionId(), auction);
+    }
+
+    /**
+     * Places a bid. See also {@link Bid}.
+     *
+     * @param bid the bid to be placed.
+     * @return false if the bid is for an auction with an unknown identifier, true otherwise
+     */
+    public boolean placeBid(Bid bid) {
+        if (!containsAuctionWithId(bid.getAuctionId())) {
+            return false;
+        }
+
+        Auction auction = getAuctionById(bid.getAuctionId()).get();
+        auction.addBid(bid);
+        auctions.put(bid.getAuctionId(), auction);
+
+        return true;
+    }
+
+    /**
+     * Checks if the registry contains an auction with the given identifier.
+     *
+     * @param auctionId the auction's identifier
+     * @return true if the registry contains an auction with the given identifier, false otherwise
+     */
+    public boolean containsAuctionWithId(Auction.AuctionId auctionId) {
+        return auctions.containsKey(auctionId);
+    }
+
+    /**
+     * Retrieves the auction with the given identifier if it exists.
+     *
+     * @param auctionId the auction's identifier
+     * @return the auction or Optional.empty if the identifier is unknown
+     */
+    public Optional<Auction> getAuctionById(Auction.AuctionId auctionId) {
+        if (containsAuctionWithId(auctionId)) {
+            return Optional.of(auctions.get(auctionId));
+        }
+
+        return Optional.empty();
+    }
+
+    /**
+     * Retrieves all auctions in the registry.
+     *
+     * @return a collection with all auctions
+     */
+    public Collection<Auction> getAllAuctions() {
+        return auctions.values();
+    }
+
+    /**
+     * Retrieves only the auctions that are open for bids.
+     *
+     * @return a collection with all open auctions
+     */
+    public Collection<Auction> getOpenAuctions() {
+        return getAllAuctions()
+            .stream()
+            .filter(auction -> auction.isOpen())
+            .collect(Collectors.toList());
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/domain/AuctionStartedEvent.java

@@ -0,0 +1,15 @@
+package ch.unisg.tapas.auctionhouse.domain;
+
+import lombok.Getter;
+
+/**
+ * A domain event that models an auction has started.
+ */
+public class AuctionStartedEvent {
+    @Getter
+    private Auction auction;
+
+    public AuctionStartedEvent(Auction auction) {
+        this.auction = auction;
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/domain/AuctionWonEvent.java

@@ -0,0 +1,16 @@
+package ch.unisg.tapas.auctionhouse.domain;
+
+import lombok.Getter;
+
+/**
+ * A domain event that models an auction was won.
+ */
+public class AuctionWonEvent {
+    // The winning bid
+    @Getter
+    private Bid winningBid;
+
+    public AuctionWonEvent(Bid winningBid) {
+        this.winningBid = winningBid;
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/domain/Bid.java

@@ -0,0 +1,66 @@
+package ch.unisg.tapas.auctionhouse.domain;
+
+import lombok.Getter;
+import lombok.Value;
+
+import java.net.URI;
+
+/**
+ * Domain entity that models a bid.
+ */
+public class Bid {
+    // The identifier of the auction for which the bid is placed
+    @Getter
+    private final Auction.AuctionId auctionId;
+
+    // The name of the bidder, i.e. the identifier of the TAPAS group
+    @Getter
+    private final BidderName bidderName;
+
+    // URI that identifies the auction house of the bidder. Given a uniform, standard HTTP API for
+    // auction houses, this URI can then be used as a base URI for interacting with the auction house
+    // of the bidder.
+    @Getter
+    private final BidderAuctionHouseUri bidderAuctionHouseUri;
+
+    // URI that identifies the TAPAS-Tasks task list of the bidder. Given a uniform, standard HTTP API
+    // for TAPAS-Tasks, this URI can then be used as a base URI for interacting with the list of tasks
+    // of the bidder, e.g. to delegate a task.
+    @Getter
+    private final BidderTaskListUri bidderTaskListUri;
+
+    /**
+     * Constructs a bid.
+     *
+     * @param auctionId the identifier of the auction for which the bid is placed
+     * @param bidderName the name of the bidder, i.e. the identifier of the TAPAS group
+     * @param auctionHouseUri the URI of the bidder's auction house
+     * @param taskListUri the URI fo the bidder's list of tasks
+     */
+    public Bid(Auction.AuctionId auctionId, BidderName bidderName, BidderAuctionHouseUri auctionHouseUri,
+            BidderTaskListUri taskListUri) {
+        this.auctionId = auctionId;
+        this.bidderName = bidderName;
+        this.bidderAuctionHouseUri = auctionHouseUri;
+        this.bidderTaskListUri = taskListUri;
+    }
+
+    /*
+     * Definitions of Value Objects
+     */
+
+    @Value
+    public static class BidderName {
+        private String value;
+    }
+
+    @Value
+    public static class BidderAuctionHouseUri {
+        private URI value;
+    }
+
+    @Value
+    public static class BidderTaskListUri {
+        private URI value;
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/auctionhouse/domain/ExecutorRegistry.java

@@ -0,0 +1,86 @@
+package ch.unisg.tapas.auctionhouse.domain;
+
+import lombok.Value;
+
+import java.util.*;
+
+/**
+ * Registry that keeps a track of executors internal to the TAPAS application and the types of tasks
+ * they can achieve. One executor may correspond to multiple task types. This mapping is used when
+ * bidding for tasks: the auction house will only bid for tasks for which there is a known executor.
+ * This class is a singleton.
+ */
+public class ExecutorRegistry {
+    private static ExecutorRegistry registry;
+
+    private final Map<Auction.AuctionedTaskType, Set<ExecutorIdentifier>> executors;
+
+    private ExecutorRegistry() {
+        this.executors = new Hashtable<>();
+    }
+
+    public static synchronized ExecutorRegistry getInstance() {
+        if (registry == null) {
+            registry = new ExecutorRegistry();
+        }
+
+        return registry;
+    }
+
+    /**
+     * Adds an executor to the registry for a given task type.
+     *
+     * @param taskType the type of the task
+     * @param executorIdentifier the identifier of the executor (can be any string)
+     * @return true unless a runtime exception occurs
+     */
+    public boolean addExecutor(Auction.AuctionedTaskType taskType, ExecutorIdentifier executorIdentifier) {
+        Set<ExecutorIdentifier> taskTypeExecs = executors.getOrDefault(taskType,
+            Collections.synchronizedSet(new HashSet<>()));
+
+        taskTypeExecs.add(executorIdentifier);
+        executors.put(taskType, taskTypeExecs);
+
+        return true;
+    }
+
+    /**
+     * Removes an executor from the registry. The executor is disassociated from all known task types.
+     *
+     * @param executorIdentifier the identifier of the executor (can be any string)
+     * @return true unless a runtime exception occurs
+     */
+    public boolean removeExecutor(ExecutorIdentifier executorIdentifier) {
+        Iterator<Auction.AuctionedTaskType> iterator = executors.keySet().iterator();
+
+        while (iterator.hasNext()) {
+            Auction.AuctionedTaskType taskType = iterator.next();
+            Set<ExecutorIdentifier> set = executors.get(taskType);
+
+            set.remove(executorIdentifier);
+
+            if (set.isEmpty()) {
+                iterator.remove();
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * Checks if the registry contains an executor for a given task type. Used during an auction to
+     * decide if a bid should be placed.
+     *
+     * @param taskType the task type being auctioned
+     * @return
+     */
+    public boolean containsTaskType(Auction.AuctionedTaskType taskType) {
+        return executors.containsKey(taskType);
+    }
+
+    // Value Object for the executor identifier
+    @Value
+    public static class ExecutorIdentifier {
+        String value;
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/common/AuctionHouseResourceDirectory.java

@@ -0,0 +1,57 @@
+package ch.unisg.tapas.common;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Class that wraps up the resource directory used to discover auction houses in Week 6.
+ */
+public class AuctionHouseResourceDirectory {
+    private final URI rdEndpoint;
+
+    /**
+     * Constructs a resource directory for auction house given a known URI.
+     *
+     * @param rdEndpoint the based endpoint of the resource directory
+     */
+    public AuctionHouseResourceDirectory(URI rdEndpoint) {
+        this.rdEndpoint = rdEndpoint;
+    }
+
+    /**
+     * Retrieves the endpoints of all auctions houses registered with this directory.
+     * @return
+     */
+    public List<String> retrieveAuctionHouseEndpoints() {
+        List<String> auctionHouseEndpoints = new ArrayList<>();
+
+        try {
+            HttpRequest request = HttpRequest.newBuilder()
+                .uri(rdEndpoint).GET().build();
+
+            HttpResponse<String> response = HttpClient.newBuilder().build()
+                .send(request, HttpResponse.BodyHandlers.ofString());
+
+            // For simplicity, here we just hard code the current representation used by our
+            // resource directory for auction houses
+            ObjectMapper objectMapper = new ObjectMapper();
+            JsonNode payload = objectMapper.readTree(response.body());
+
+            for (JsonNode node : payload) {
+                auctionHouseEndpoints.add(node.get("endpoint").asText());
+            }
+        } catch (IOException | InterruptedException e) {
+            e.printStackTrace();
+        }
+
+        return auctionHouseEndpoints;
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/common/ConfigProperties.java

@@ -0,0 +1,64 @@
+package ch.unisg.tapas.common;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.core.env.Environment;
+import org.springframework.stereotype.Component;
+
+import java.net.URI;
+
+/**
+ * Used to access properties provided via application.properties
+ */
+@Component
+public class ConfigProperties {
+    @Autowired
+    private Environment environment;
+
+    /**
+     * Retrieves the URI of the WebSub hub. In this project, we use a single WebSub hub, but we could
+     * use multiple.
+     *
+     * @return the URI of the WebSub hub
+     */
+    public URI getWebSubHub() {
+        return URI.create(environment.getProperty("websub.hub"));
+    }
+
+    /**
+     * Retrieves the URI used to publish content via WebSub. In this project, we use a single
+     * WebSub hub, but we could use multiple. This URI is usually different from the WebSub hub URI.
+     *
+     * @return URI used to publish content via the WebSub hub
+     */
+    public URI getWebSubPublishEndpoint() {
+        return URI.create(environment.getProperty("websub.hub.publish"));
+    }
+
+    /**
+     * Retrieves the name of the group providing this auction house.
+     *
+     * @return the identifier of the group, e.g. tapas-group1
+     */
+    public String getGroupName() {
+        return environment.getProperty("group");
+    }
+
+    /**
+     * Retrieves the base URI of this auction house.
+     *
+     * @return the base URI of this auction house
+     */
+    public URI getAuctionHouseUri() {
+        return URI.create(environment.getProperty("auction.house.uri"));
+    }
+
+    /**
+     * Retrieves the URI of the TAPAS-Tasks task list of this TAPAS applicatoin. This is used, e.g.,
+     * when placing a bid during the auction (see also {@link ch.unisg.tapas.auctionhouse.domain.Bid}).
+     *
+     * @return
+     */
+    public URI getTaskListUri() {
+        return URI.create(environment.getProperty("tasks.list.uri"));
+    }
+}

tapas-auction-house/src/main/java/ch/unisg/tapas/common/SelfValidating.java

@@ -0,0 +1,25 @@
+package ch.unisg.tapas.common;
+
+import javax.validation.*;
+import java.util.Set;
+
+public class SelfValidating<T> {
+
+    private Validator validator;
+
+    public SelfValidating() {
+        ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
+        validator = factory.getValidator();
+    }
+
+    /**
+     * Evaluates all Bean Validations on the attributes of this
+     * instance.
+     */
+    protected void validateSelf() {
+        Set<ConstraintViolation<T>> violations = validator.validate((T) this);
+        if (!violations.isEmpty()) {
+            throw new ConstraintViolationException(violations);
+        }
+    }
+}

tapas-auction-house/src/main/resources/application.properties

@@ -0,0 +1,8 @@
+server.port=8082
+
+websub.hub=https://websub.appspot.com/
+websub.hub.publish=https://websub.appspot.com/
+
+group=tapas-group-tutors
+auction.house.uri=https://tapas-auction-house.86-119-34-23.nip.io/
+tasks.list.uri=https://tapas-tasks.86-119-34-23.nip.io/

tapas-auction-house/src/test/java/ch/unisg/tapas/TapasAuctionHouseApplicationTests.java

@@ -0,0 +1,13 @@
+package ch.unisg.tapas;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.test.context.SpringBootTest;
+
+@SpringBootTest
+class TapasAuctionHouseApplicationTests {
+
+	@Test
+	void contextLoads() {
+	}
+
+}

tapas-tasks/README.md

@@ -11,61 +11,159 @@ with default editor settings. EditorConfig is supported out-of-the-box by the In
 consistent code styles, we recommend to reuse this editor configuration file in all your services.
 
 ## HTTP API Overview
-The code we provide includes a minimalistic HTTP API for (i) creating a new task and (ii) retrieving
+The code we provide includes a minimalistic uniform HTTP API for (i) creating a new task, (ii) retrieving
-the representation of a task.
+a representation of the current state of a task, and (iii) patching the representation of a task, which
+is mapped to a domain/integration event.
+
+The representations exchanged with the API use two media types:
+* a JSON-based format for task with the media type `application/task+json`; this media type is defined
+  in the context of our project, but could be [registered with IANA](https://www.iana.org/assignments/media-types)
+  to promote interoperability (see
+  [TaskJsonRepresentation](src/main/java/ch/unisg/tapastasks/tasks/adapter/in/formats/TaskJsonRepresentation.java)
+  for more details)
+* the [JSON Patch](http://jsonpatch.com/) format with the registered media type `application/json-patch+json`, which is also a
+  JSON-based format (see sample HTTP requests below).
 
 For further developing and working with your HTTP API, we recommend to use [Postman](https://www.postman.com/).
 
 ### Creating a new task
 
 A new task is created via an `HTTP POST` request to the `/tasks/` endpoint. The body of the request
-must include a JSON payload with the content type `application/json` and two required fields:
+must include a representation of the task to be created using the content type `application/task+json`
+defined in the context of this project. A valid representation must include at least two required fields
+(see [TaskJsonRepresentation](src/main/java/ch/unisg/tapastasks/tasks/adapter/in/formats/TaskJsonRepresentation.java)
+for more details):
 * `taskName`: a string that represents the name of the task to be created
 * `taskType`: a string that represents the type of the task to be created
 
 A sample HTTP request with `curl`:
 ```shell
-curl -i --location --request POST 'http://localhost:8081/tasks/' --header 'Content-Type: application/json' --data-raw '{
+curl -i --location --request POST 'http://localhost:8081/tasks/' \
+--header 'Content-Type: application/task+json' \
+--data-raw '{
   "taskName" : "task1",
-    "taskType" : "type1"
+  "taskType" : "computation",
+  "originalTaskUri" : "http://example.org",
+  "inputData" : "1+1"
 }'
 
 HTTP/1.1 201
-Content-Type: application/json
+Location: http://localhost:8081/tasks/cef2fa9d-367b-4e7f-bf06-3b1fea35f354
-Content-Length: 142
+Content-Type: application/task+json
-Date: Sun, 03 Oct 2021 17:25:32 GMT
+Content-Length: 170
+Date: Sun, 17 Oct 2021 21:03:34 GMT
 
 {
-  "taskType" : "type1",
+  "taskId":"cef2fa9d-367b-4e7f-bf06-3b1fea35f354",
-  "taskState" : "OPEN",
-  "taskListName" : "tapas-tasks-tutors",
   "taskName":"task1",
-  "taskId" : "53cb19d6-2d9b-486f-98c7-c96c93b037f0"
+  "taskType":"computation",
+  "taskStatus":"OPEN",
+  "originalTaskUri":"http://example.org",
+  "inputData":"1+1"
 }
 ```
 
-If the task is created successfuly, a `201 Created` status code is returned together with a JSON
+If the task is created successfuly, a `201 Created` status code is returned together with a
-representation of the created task. The representation includes, among others, a _universally unique
+representation of the created task. The response also includes a `Location` header filed that points
-identifier (UUID)_ for the newly created task (`taskId`).
+to the URI of the newly created task.
 
 ### Retrieving a task
 
-The representation of a task is retrieved via an `HTTP GET` request to the `/tasks/<task-UUID>` endpoint.
+The representation of a task is retrieved via an `HTTP GET` request to the URI of task.
 
 A sample HTTP request with `curl`:
 ```shell
-curl -i --location --request GET 'http://localhost:8081/tasks/53cb19d6-2d9b-486f-98c7-c96c93b037f0'
+curl -i --location --request GET 'http://localhost:8081/tasks/cef2fa9d-367b-4e7f-bf06-3b1fea35f354'
 
 HTTP/1.1 200
-Content-Type: application/json
+Content-Type: application/task+json
-Content-Length: 142
+Content-Length: 170
-Date: Sun, 03 Oct 2021 17:27:06 GMT
+Date: Sun, 17 Oct 2021 21:07:04 GMT
 
 {
-  "taskType" : "type1",
+  "taskId":"cef2fa9d-367b-4e7f-bf06-3b1fea35f354",
-  "taskState" : "OPEN",
-  "taskListName" : "tapas-tasks-tutors",
   "taskName":"task1",
-  "taskId" : "53cb19d6-2d9b-486f-98c7-c96c93b037f0"
+  "taskType":"computation",
+  "taskStatus":"OPEN",
+  "originalTaskUri":"http://example.org",
+  "inputData":"1+1"
 }
 ```
+
+### Patching a task
+
+REST emphasizes the generality of interfaces to promote uniform interaction. For instance, we can use
+the `HTTP PATCH` method to implement fine-grained updates to the representational state of a task, which
+may translate to various domain/integration events. However, to conform to the uniform interface
+contraint in REST, any such updates have to rely on standard knowledge — and thus to hide away the
+implementation details of our service.
+
+In addition to the `application/task+json` media type we defined for our uniform HTTP API, a standard
+representation format we can use to specify fine-grained updates to the representation of tasks
+is [JSON Patch](http://jsonpatch.com/). In what follow, we provide a few examples of `HTTP PATCH` requests.
+For further details on the JSON Patch format, see also [RFC 6902](https://datatracker.ietf.org/doc/html/rfc6902)).
+
+#### Changing the status of a task from OPEN to ASSIGNED
+
+Sample HTTP request that assigns the previously created task to group `tapas-group1`:
+
+```shell
+curl -i --location --request PATCH 'http://localhost:8081/tasks/cef2fa9d-367b-4e7f-bf06-3b1fea35f354' \
+--header 'Content-Type: application/json-patch+json' \
+--data-raw '[ {"op" : "replace", "path": "/taskStatus", "value" : "ASSIGNED" },
+  {"op" : "add", "path": "/serviceProvider", "value" : "tapas-group1" } ]'
+
+HTTP/1.1 200
+Content-Type: application/task+json
+Content-Length: 207
+Date: Sun, 17 Oct 2021 21:20:58 GMT
+
+{
+  "taskId":"cef2fa9d-367b-4e7f-bf06-3b1fea35f354",
+  "taskName":"task1",
+  "taskType":"computation",
+  "taskStatus":"ASSIGNED",
+  "originalTaskUri":"http://example.org",
+  "serviceProvider":"tapas-group1",
+  "inputData":"1+1"
+}
+```
+
+In this example, the requested patch includes two JSON Patch operations:
+* an operation to `replace` the `taskStatus` already in the task's representation with the value `ASSIGNED`
+* an operation to `add` to the task's representation a `serviceProvider` with the value `tapas-group1`
+
+Internally, this request is mapped to a
+[TaskAssignedEvent](src/main/java/ch/unisg/tapastasks/tasks/application/port/in/TaskAssignedEvent.java).
+The HTTP response returns a `200 OK` status code together with the updated representation of the task.
+
+#### Changing the status of a task from to EXECUTED
+
+Sample HTTP request that changes the status of the task to `EXECUTED` and adds an output result:
+
+```shell
+curl -i --location --request PATCH 'http://localhost:8081/tasks/cef2fa9d-367b-4e7f-bf06-3b1fea35f354' \
+--header 'Content-Type: application/json-patch+json' \
+--data-raw '[ {"op" : "replace", "path": "/taskStatus", "value" : "EXECUTED" },
+  {"op" : "add", "path": "/outputData", "value" : "2" } ]'
+
+HTTP/1.1 200
+Content-Type: application/task+json
+Content-Length: 224
+Date: Sun, 17 Oct 2021 21:32:25 GMT
+
+{
+  "taskId":"cef2fa9d-367b-4e7f-bf06-3b1fea35f354",
+  "taskName":"task1",
+  "taskType":"computation",
+  "taskStatus":"EXECUTED",
+  "originalTaskUri":"http://example.org",
+  "serviceProvider":"tapas-group1",
+  "inputData":"1+1",
+  "outputData":"2"
+}
+```
+
+Internally, this request is mapped to a
+[TaskExecutedEvent](src/main/java/ch/unisg/tapastasks/tasks/application/port/in/TaskExecutedEvent.java).
+The HTTP response returns a `200 OK` status code together with the updated representation of the task.

tapas-tasks/pom.xml

@@ -16,6 +16,12 @@
 	<properties>
 		<java.version>11</java.version>
 	</properties>
+    <repositories>
+        <repository>
+            <id>Eclipse Paho Repo</id>
+            <url>https://repo.eclipse.org/content/repositories/paho-releases/</url>
+        </repository>
+    </repositories>
 	<dependencies>
 		<dependency>
 			<groupId>org.springframework.boot</groupId>
@@ -49,17 +55,16 @@
             <version>1.1.0.Final</version>
         </dependency>
 
-		<dependency>
-			<groupId>org.json</groupId>
-			<artifactId>json</artifactId>
-			<version>20210307</version>
-		</dependency>
 		<dependency>
 			<groupId>com.github.java-json-tools</groupId>
 			<artifactId>json-patch</artifactId>
 			<version>1.13</version>
 		</dependency>
-
+        <dependency>
+            <groupId>org.eclipse.paho</groupId>
+            <artifactId>org.eclipse.paho.client.mqttv3</artifactId>
+            <version>1.2.0</version>
+        </dependency>
     </dependencies>
 
 	<build>

tapas-tasks/src/main/java/ch/unisg/tapastasks/TapasTasksApplication.java

@@ -3,13 +3,10 @@ package ch.unisg.tapastasks;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 
-import java.util.Collections;
-
 @SpringBootApplication
 public class TapasTasksApplication {
 
 	public static void main(String[] args) {
-
 		SpringApplication tapasTasksApp = new SpringApplication(TapasTasksApplication.class);
 		tapasTasksApp.run(args);
 	}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/adapter/in/formats/TaskJsonPatchRepresentation.java

@@ -0,0 +1,102 @@
+package ch.unisg.tapastasks.tasks.adapter.in.formats;
+
+import ch.unisg.tapastasks.tasks.domain.Task;
+import com.fasterxml.jackson.databind.JsonNode;
+
+import java.util.Optional;
+import java.util.function.Predicate;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+/**
+ * This class is used to process JSON Patch operations for tasks: given a
+ * <a href="http://jsonpatch.com/">JSON Patch</a> for updating the representational state of a task,
+ * this class provides methods for extracting various operations of interest for our domain (e.g.,
+ * changing the status of a task).
+ */
+public class TaskJsonPatchRepresentation {
+    public static final String MEDIA_TYPE = "application/json-patch+json";
+
+    private final JsonNode patch;
+
+    /**
+     * Constructs the JSON Patch representation.
+     *
+     * @param patch a JSON Patch as JsonNode
+     */
+    public TaskJsonPatchRepresentation(JsonNode patch) {
+        this.patch = patch;
+    }
+
+    /**
+     * Extracts the first task status replaced in this patch.
+     *
+     * @return the first task status changed in this patch or an empty {@link Optional} if none is
+     * found
+     */
+    public Optional<Task.Status> extractFirstTaskStatusChange() {
+        Optional<JsonNode> status = extractFirst(node ->
+            isPatchReplaceOperation(node) && hasPath(node, "/taskStatus")
+        );
+
+        if (status.isPresent()) {
+            String taskStatus = status.get().get("value").asText();
+            return Optional.of(Task.Status.valueOf(taskStatus));
+        }
+
+        return Optional.empty();
+    }
+
+    /**
+     * Extracts the first service provider added or replaced in this patch.
+     *
+     * @return the first service provider changed in this patch or an empty {@link Optional} if none
+     * is found
+     */
+    public Optional<Task.ServiceProvider> extractFirstServiceProviderChange() {
+        Optional<JsonNode> serviceProvider = extractFirst(node ->
+                (isPatchReplaceOperation(node) || isPatchAddOperation(node))
+                && hasPath(node, "/serviceProvider")
+        );
+
+        return (serviceProvider.isEmpty()) ? Optional.empty()
+            : Optional.of(new Task.ServiceProvider(serviceProvider.get().get("value").asText()));
+    }
+
+    /**
+     * Extracts the first output data addition in this patch.
+     *
+     * @return the output data added in this patch or an empty {@link Optional} if none is found
+     */
+    public Optional<Task.OutputData> extractFirstOutputDataAddition() {
+        Optional<JsonNode> output = extractFirst(node ->
+            isPatchAddOperation(node) && hasPath(node, "/outputData")
+        );
+
+        return (output.isEmpty()) ? Optional.empty()
+            : Optional.of(new Task.OutputData(output.get().get("value").asText()));
+    }
+
+    private Optional<JsonNode> extractFirst(Predicate<? super JsonNode> predicate) {
+        Stream<JsonNode> stream = StreamSupport.stream(patch.spliterator(), false);
+        return stream.filter(predicate).findFirst();
+    }
+
+    private boolean isPatchAddOperation(JsonNode node) {
+        return isPatchOperationOfType(node, "add");
+    }
+
+    private boolean isPatchReplaceOperation(JsonNode node) {
+        return isPatchOperationOfType(node, "replace");
+    }
+
+    private boolean isPatchOperationOfType(JsonNode node, String operation) {
+        return node.isObject() && node.get("op") != null
+            && node.get("op").asText().equalsIgnoreCase(operation);
+    }
+
+    private boolean hasPath(JsonNode node, String path) {
+        return node.isObject() && node.get("path") != null
+            && node.get("path").asText().equalsIgnoreCase(path);
+    }
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/adapter/in/formats/TaskJsonRepresentation.java

@@ -0,0 +1,115 @@
+package ch.unisg.tapastasks.tasks.adapter.in.formats;
+
+import ch.unisg.tapastasks.tasks.domain.Task;
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import lombok.Getter;
+import lombok.Setter;
+
+/**
+ * This class is used to expose and consume representations of tasks through the HTTP interface. The
+ * representations conform to the custom JSON-based media type "application/task+json". The media type
+ * is just an identifier and can be registered with
+ * <a href="https://www.iana.org/assignments/media-types/">IANA</a> to promote interoperability.
+ */
+final public class TaskJsonRepresentation {
+    // The media type used for this task representation format
+    public static final String MEDIA_TYPE = "application/task+json";
+
+    // A task identifier specific to our implementation (e.g., a UUID). This identifier is then used
+    // to generate the task's URI. URIs are standard uniform identifiers and use a universal syntax
+    // that can be referenced (and dereferenced) independent of context. In our uniform HTTP API,
+    // we identify tasks via URIs and not implementation-specific identifiers.
+    @Getter @Setter
+    private String taskId;
+
+    // A string that represents the task's name
+    @Getter
+    private final String taskName;
+
+    // A string that identifies the task's type. This string could also be a URI (e.g., defined in some
+    // Web ontology, as we shall see later in the course), but it's not constrained to be a URI.
+    // The task's type can be used to assign executors to tasks, to decide what tasks to bid for, etc.
+    @Getter
+    private final String taskType;
+
+    // The task's status: OPEN, ASSIGNED, RUNNING, or EXECUTED (see Task.Status)
+    @Getter @Setter
+    private String taskStatus;
+
+    // If this task is a delegated task (i.e., a shadow of another task), this URI points to the
+    // original task. Because URIs are standard and uniform, we can just dereference this URI to
+    // retrieve a representation of the original task.
+    @Getter @Setter
+    private String originalTaskUri;
+
+    // The service provider who executes this task. The service provider is a any string that identifies
+    // a TAPAS group (e.g., tapas-group1). This identifier could also be a URI (if we have a good reason
+    // for it), but it's not constrained to be a URI.
+    @Getter @Setter
+    private String serviceProvider;
+
+    // A string that provides domain-specific input data for this task. In the context of this project,
+    // we can parse and interpret the input data based on the task's type.
+    @Getter @Setter
+    private String inputData;
+
+    // A string that provides domain-specific output data for this task. In the context of this project,
+    // we can parse and interpret the output data based on the task's type.
+    @Getter @Setter
+    private String outputData;
+
+    /**
+     * Instantiate a task representation with a task name and type.
+     *
+     * @param taskName string that represents the task's name
+     * @param taskType string that represents the task's type
+     */
+    public TaskJsonRepresentation(String taskName, String taskType) {
+        this.taskName = taskName;
+        this.taskType = taskType;
+
+        this.taskStatus = null;
+        this.originalTaskUri = null;
+        this.serviceProvider = null;
+        this.inputData = null;
+        this.outputData = null;
+    }
+
+    /**
+     * Instantiate a task representation from a domain concept.
+     *
+     * @param task the task
+     */
+    public TaskJsonRepresentation(Task task) {
+        this(task.getTaskName().getValue(), task.getTaskType().getValue());
+
+        this.taskId = task.getTaskId().getValue();
+        this.taskStatus = task.getTaskStatus().getValue().name();
+
+        this.originalTaskUri = (task.getOriginalTaskUri() == null) ?
+            null : task.getOriginalTaskUri().getValue();
+
+        this.serviceProvider = (task.getProvider() == null) ? null : task.getProvider().getValue();
+        this.inputData = (task.getInputData() == null) ? null : task.getInputData().getValue();
+        this.outputData = (task.getOutputData() == null) ? null : task.getOutputData().getValue();
+    }
+
+    /**
+     * Convenience method used to serialize a task provided as a domain concept in the format exposed
+     * through the uniform HTTP API.
+     *
+     * @param task the task as defined in the domain
+     * @return a string serialization using the JSON-based representation format defined for tasks
+     * @throws JsonProcessingException if a runtime exception occurs during object serialization
+     */
+    public static String serialize(Task task) throws JsonProcessingException {
+        TaskJsonRepresentation representation = new TaskJsonRepresentation(task);
+
+        ObjectMapper mapper = new ObjectMapper();
+        mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
+
+        return mapper.writeValueAsString(representation);
+    }
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/adapter/in/messaging/UnknownEventException.java

@@ -0,0 +1,3 @@
+package ch.unisg.tapastasks.tasks.adapter.in.messaging;
+
+public class UnknownEventException extends RuntimeException { }

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/adapter/in/messaging/http/TaskAssignedEventListenerHttpAdapter.java

@@ -0,0 +1,39 @@
+package ch.unisg.tapastasks.tasks.adapter.in.messaging.http;
+
+import ch.unisg.tapastasks.tasks.adapter.in.formats.TaskJsonPatchRepresentation;
+import ch.unisg.tapastasks.tasks.application.handler.TaskAssignedHandler;
+import ch.unisg.tapastasks.tasks.application.port.in.TaskAssignedEvent;
+import ch.unisg.tapastasks.tasks.application.port.in.TaskAssignedEventHandler;
+import ch.unisg.tapastasks.tasks.domain.Task;
+import ch.unisg.tapastasks.tasks.domain.Task.TaskId;
+import com.fasterxml.jackson.databind.JsonNode;
+
+import java.util.Optional;
+
+/**
+ * Listener for task assigned events. A task assigned event corresponds to a JSON Patch that attempts
+ * to change the task's status to ASSIGNED and may also add/replace a service provider (i.e., to what
+ * group the task was assigned). This implementation does not impose that a task assigned event
+ * includes the service provider (i.e., can be null).
+ *
+ * See also {@link TaskAssignedEvent}, {@link Task}, and {@link TaskEventHttpDispatcher}.
+ */
+public class TaskAssignedEventListenerHttpAdapter extends TaskEventListener {
+
+    /**
+     * Handles the task assigned event.
+     *
+     * @param taskId the identifier of the task for which an event was received
+     * @param payload the JSON Patch payload of the HTTP PATCH request received for this task
+     * @return
+     */
+    public Task handleTaskEvent(String taskId, JsonNode payload) {
+        TaskJsonPatchRepresentation representation = new TaskJsonPatchRepresentation(payload);
+        Optional<Task.ServiceProvider> serviceProvider = representation.extractFirstServiceProviderChange();
+
+        TaskAssignedEvent taskAssignedEvent = new TaskAssignedEvent(new TaskId(taskId), serviceProvider);
+        TaskAssignedEventHandler taskAssignedEventHandler = new TaskAssignedHandler();
+
+        return taskAssignedEventHandler.handleTaskAssigned(taskAssignedEvent);
+    }
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/adapter/in/messaging/http/TaskEventHttpDispatcher.java

@@ -0,0 +1,103 @@
+package ch.unisg.tapastasks.tasks.adapter.in.messaging.http;
+
+import ch.unisg.tapastasks.tasks.adapter.in.formats.TaskJsonPatchRepresentation;
+import ch.unisg.tapastasks.tasks.adapter.in.formats.TaskJsonRepresentation;
+import ch.unisg.tapastasks.tasks.adapter.in.messaging.UnknownEventException;
+import ch.unisg.tapastasks.tasks.domain.Task;
+import ch.unisg.tapastasks.tasks.domain.TaskNotFoundException;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.github.fge.jsonpatch.JsonPatch;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.PatchMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.server.ResponseStatusException;
+
+import java.io.IOException;
+import java.util.Optional;
+
+
+/**
+ * This REST Controller handles HTTP PATCH requests for updating the representational state of Task
+ * resources. Each request to update the representational state of a Task resource can correspond to
+ * at most one domain/integration event. Request payloads use the
+ * <a href="http://jsonpatch.com/">JSON PATCH</a> format and media type.
+ *
+ * A JSON Patch can contain multiple operations (e.g., add, remove, replace) for updating various
+ * parts of a task's representations. One or more JSON Patch operations can represent a domain/integration
+ * event. Therefore, the events can only be determined by inspecting the requested patch (e.g., a request
+ * to change a task's status from RUNNING to EXECUTED). This class is responsible to inspect requested
+ * patches, identify events, and to route them to appropriate listeners.
+ *
+ * For more details on JSON Patch, see: <a href="http://jsonpatch.com/">http://jsonpatch.com/</a>
+ * For some sample HTTP requests, see the README.
+ */
+@RestController
+public class TaskEventHttpDispatcher {
+    // The standard media type for JSON Patch registered with IANA
+    // See: https://www.iana.org/assignments/media-types/application/json-patch+json
+    private final static String JSON_PATCH_MEDIA_TYPE = "application/json-patch+json";
+
+    /**
+     * Handles HTTP PATCH requests with a JSON Patch payload. Routes the requests based on the
+     * the operations requested in the patch. In this implementation, one HTTP Patch request is
+     * mapped to at most one domain event.
+     *
+     * @param taskId the local (i.e., implementation-specific) identifier of the task to the patched;
+     *               this identifier is extracted from the task's URI
+     * @param payload the reuqested patch for this task
+     * @return 200 OK and a representation of the task after processing the event; 404 Not Found if
+     * the request URI does not match any task; 400 Bad Request if the request is invalid
+     */
+    @PatchMapping(path = "/tasks/{taskId}", consumes = {JSON_PATCH_MEDIA_TYPE})
+    public ResponseEntity<String> dispatchTaskEvents(@PathVariable("taskId") String taskId,
+            @RequestBody JsonNode payload) {
+        try {
+            // Throw an exception if the JSON Patch format is invalid. This call is only used to
+            // validate the JSON PATCH syntax.
+            JsonPatch.fromJson(payload);
+
+            // Check for known events and route the events to appropriate listeners
+            TaskJsonPatchRepresentation representation = new TaskJsonPatchRepresentation(payload);
+            Optional<Task.Status> status = representation.extractFirstTaskStatusChange();
+
+            TaskEventListener listener = null;
+
+            // Route events related to task status changes
+            if (status.isPresent()) {
+                switch (status.get()) {
+                    case ASSIGNED:
+                        listener = new TaskAssignedEventListenerHttpAdapter();
+                        break;
+                    case RUNNING:
+                        listener = new TaskStartedEventListenerHttpAdapter();
+                        break;
+                    case EXECUTED:
+                        listener = new TaskExecutedEventListenerHttpAdapter();
+                        break;
+                }
+            }
+
+            if (listener == null) {
+                // The HTTP PATCH request is valid, but the patch does not match any known event
+                throw new UnknownEventException();
+            }
+
+            Task task = listener.handleTaskEvent(taskId, payload);
+
+            // Add the content type as a response header
+            HttpHeaders responseHeaders = new HttpHeaders();
+            responseHeaders.add(HttpHeaders.CONTENT_TYPE, TaskJsonRepresentation.MEDIA_TYPE);
+
+            return new ResponseEntity<>(TaskJsonRepresentation.serialize(task), responseHeaders,
+                HttpStatus.OK);
+        } catch (TaskNotFoundException e) {
+            throw new ResponseStatusException(HttpStatus.NOT_FOUND);
+        } catch (IOException | RuntimeException e) {
+            throw new ResponseStatusException(HttpStatus.BAD_REQUEST, e.getMessage());
+        }
+    }
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/adapter/in/messaging/http/TaskEventListener.java

@@ -0,0 +1,24 @@
+package ch.unisg.tapastasks.tasks.adapter.in.messaging.http;
+
+import ch.unisg.tapastasks.tasks.domain.Task;
+import ch.unisg.tapastasks.tasks.domain.TaskNotFoundException;
+import com.fasterxml.jackson.databind.JsonNode;
+
+/**
+ * Abstract class that handles events specific to a Task. Events are received via an HTTP PATCH
+ * request for a given task and dispatched to Task event listeners (see {@link TaskEventHttpDispatcher}).
+ * Each listener must implement the abstract method {@link #handleTaskEvent(String, JsonNode)}, which
+ * may require additional event-specific validations.
+ */
+public abstract class TaskEventListener {
+
+    /**
+     * This abstract method handles a task event and returns the task after the event was handled.
+     *
+     * @param taskId the identifier of the task for which an event was received
+     * @param payload the JSON Patch payload of the HTTP PATCH request received for this task
+     * @return the task for which the HTTP PATCH request is handled
+     * @throws TaskNotFoundException
+     */
+    public abstract Task handleTaskEvent(String taskId, JsonNode payload) throws TaskNotFoundException;
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/adapter/in/messaging/http/TaskExecutedEventListenerHttpAdapter.java

@@ -0,0 +1,34 @@
+package ch.unisg.tapastasks.tasks.adapter.in.messaging.http;
+
+import ch.unisg.tapastasks.tasks.adapter.in.formats.TaskJsonPatchRepresentation;
+import ch.unisg.tapastasks.tasks.application.handler.TaskExecutedHandler;
+import ch.unisg.tapastasks.tasks.application.port.in.TaskExecutedEvent;
+import ch.unisg.tapastasks.tasks.application.port.in.TaskExecutedEventHandler;
+import ch.unisg.tapastasks.tasks.domain.Task;
+import com.fasterxml.jackson.databind.JsonNode;
+
+import java.util.Optional;
+
+/**
+ * Listener for task executed events. A task executed event corresponds to a JSON Patch that attempts
+ * to change the task's status to EXECUTED, may add/replace a service provider, and may also add an
+ * output result. This implementation does not impose that a task executed event includes either the
+ * service provider or an output result (i.e., both can be null).
+ *
+ * See also {@link TaskExecutedEvent}, {@link Task}, and {@link TaskEventHttpDispatcher}.
+ */
+public class TaskExecutedEventListenerHttpAdapter extends TaskEventListener {
+
+    public Task handleTaskEvent(String taskId, JsonNode payload) {
+        TaskJsonPatchRepresentation representation = new TaskJsonPatchRepresentation(payload);
+
+        Optional<Task.ServiceProvider> serviceProvider = representation.extractFirstServiceProviderChange();
+        Optional<Task.OutputData> outputData = representation.extractFirstOutputDataAddition();
+
+        TaskExecutedEvent taskExecutedEvent = new TaskExecutedEvent(new Task.TaskId(taskId),
+            serviceProvider, outputData);
+        TaskExecutedEventHandler taskExecutedEventHandler = new TaskExecutedHandler();
+
+        return taskExecutedEventHandler.handleTaskExecuted(taskExecutedEvent);
+    }
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/adapter/in/messaging/http/TaskStartedEventListenerHttpAdapter.java

@@ -0,0 +1,32 @@
+package ch.unisg.tapastasks.tasks.adapter.in.messaging.http;
+
+import ch.unisg.tapastasks.tasks.adapter.in.formats.TaskJsonPatchRepresentation;
+import ch.unisg.tapastasks.tasks.application.handler.TaskStartedHandler;
+import ch.unisg.tapastasks.tasks.application.port.in.TaskStartedEvent;
+import ch.unisg.tapastasks.tasks.application.port.in.TaskStartedEventHandler;
+import ch.unisg.tapastasks.tasks.domain.Task;
+import ch.unisg.tapastasks.tasks.domain.Task.TaskId;
+import com.fasterxml.jackson.databind.JsonNode;
+
+import java.util.Optional;
+
+/**
+ * Listener for task started events. A task started event corresponds to a JSON Patch that attempts
+ * to change the task's status to RUNNING and may also add/replace a service provider. This
+ * implementation does not impose that a task started event includes the service provider (i.e.,
+ * can be null).
+ *
+ * See also {@link TaskStartedEvent}, {@link Task}, and {@link TaskEventHttpDispatcher}.
+ */
+public class TaskStartedEventListenerHttpAdapter extends TaskEventListener {
+
+    public Task handleTaskEvent(String taskId, JsonNode payload) {
+        TaskJsonPatchRepresentation representation = new TaskJsonPatchRepresentation(payload);
+        Optional<Task.ServiceProvider> serviceProvider = representation.extractFirstServiceProviderChange();
+
+        TaskStartedEvent taskStartedEvent = new TaskStartedEvent(new TaskId(taskId), serviceProvider);
+        TaskStartedEventHandler taskStartedEventHandler = new TaskStartedHandler();
+
+        return taskStartedEventHandler.handleTaskStarted(taskStartedEvent);
+    }
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/adapter/in/web/AddNewTaskToTaskListWebController.java

@@ -1,8 +1,12 @@
 package ch.unisg.tapastasks.tasks.adapter.in.web;
 
+import ch.unisg.tapastasks.tasks.adapter.in.formats.TaskJsonRepresentation;
 import ch.unisg.tapastasks.tasks.application.port.in.AddNewTaskToTaskListCommand;
 import ch.unisg.tapastasks.tasks.application.port.in.AddNewTaskToTaskListUseCase;
 import ch.unisg.tapastasks.tasks.domain.Task;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.core.env.Environment;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
@@ -12,29 +16,67 @@ import org.springframework.web.bind.annotation.RestController;
 import org.springframework.web.server.ResponseStatusException;
 
 import javax.validation.ConstraintViolationException;
+import java.util.Optional;
 
+/**
+ * Controller that handles HTTP requests for creating new tasks. This controller implements the
+ * {@link AddNewTaskToTaskListUseCase} use case using the {@link AddNewTaskToTaskListCommand}.
+ *
+ * A new task is created via an HTTP POST request to the /tasks/ endpoint. The body of the request
+ * contains a JSON-based representation with the "application/task+json" media type defined for this
+ * project. This custom media type allows to capture the semantics of our JSON representations for
+ * tasks.
+ *
+ * If the request is successful, the controller returns an HTTP 201 Created status code and a
+ * representation of the created task with Content-Type "application/task+json". The HTTP response
+ * also include a Location header field that points to the URI of the created task.
+ */
 @RestController
 public class AddNewTaskToTaskListWebController {
     private final AddNewTaskToTaskListUseCase addNewTaskToTaskListUseCase;
 
+    // Used to retrieve properties from application.properties
+    @Autowired
+    private Environment environment;
+
     public AddNewTaskToTaskListWebController(AddNewTaskToTaskListUseCase addNewTaskToTaskListUseCase) {
         this.addNewTaskToTaskListUseCase = addNewTaskToTaskListUseCase;
     }
 
-    @PostMapping(path = "/tasks/", consumes = {TaskMediaType.TASK_MEDIA_TYPE})
+    @PostMapping(path = "/tasks/", consumes = {TaskJsonRepresentation.MEDIA_TYPE})
-    public ResponseEntity<String> addNewTaskTaskToTaskList(@RequestBody Task task) {
+    public ResponseEntity<String> addNewTaskTaskToTaskList(@RequestBody TaskJsonRepresentation payload) {
         try {
-            AddNewTaskToTaskListCommand command = new AddNewTaskToTaskListCommand(
+            Task.TaskName taskName = new Task.TaskName(payload.getTaskName());
-                    task.getTaskName(), task.getTaskType()
+            Task.TaskType taskType = new Task.TaskType(payload.getTaskType());
-            );
 
-            Task newTask = addNewTaskToTaskListUseCase.addNewTaskToTaskList(command);
+            // If the created task is a delegated task, the representation contains a URI reference
+            // to the original task
+            Optional<Task.OriginalTaskUri> originalTaskUriOptional =
+                (payload.getOriginalTaskUri() == null) ? Optional.empty()
+                : Optional.of(new Task.OriginalTaskUri(payload.getOriginalTaskUri()));
+
+            AddNewTaskToTaskListCommand command = new AddNewTaskToTaskListCommand(taskName, taskType,
+                originalTaskUriOptional);
+
+            Task createdTask = addNewTaskToTaskListUseCase.addNewTaskToTaskList(command);
+
+            // When creating a task, the task's representation may include optional input data
+            if (payload.getInputData() != null) {
+                createdTask.setInputData(new Task.InputData(payload.getInputData()));
+            }
 
             // Add the content type as a response header
             HttpHeaders responseHeaders = new HttpHeaders();
-            responseHeaders.add(HttpHeaders.CONTENT_TYPE, TaskMediaType.TASK_MEDIA_TYPE);
+            responseHeaders.add(HttpHeaders.CONTENT_TYPE, TaskJsonRepresentation.MEDIA_TYPE);
+            // Construct and advertise the URI of the newly created task; we retrieve the base URI
+            // from the application.properties file
+            responseHeaders.add(HttpHeaders.LOCATION, environment.getProperty("baseuri")
+                + "tasks/" + createdTask.getTaskId().getValue());
 
-            return new ResponseEntity<>(TaskMediaType.serialize(newTask), responseHeaders, HttpStatus.CREATED);
+            return new ResponseEntity<>(TaskJsonRepresentation.serialize(createdTask), responseHeaders,
+                HttpStatus.CREATED);
+        } catch (JsonProcessingException e) {
+            throw new ResponseStatusException(HttpStatus.INTERNAL_SERVER_ERROR, e.getMessage());
         } catch (ConstraintViolationException e) {
             throw new ResponseStatusException(HttpStatus.BAD_REQUEST, e.getMessage());
         }

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/adapter/in/web/RetrieveTaskFromTaskListWebController.java

@@ -1,8 +1,10 @@
 package ch.unisg.tapastasks.tasks.adapter.in.web;
 
+import ch.unisg.tapastasks.tasks.adapter.in.formats.TaskJsonRepresentation;
 import ch.unisg.tapastasks.tasks.application.port.in.RetrieveTaskFromTaskListQuery;
 import ch.unisg.tapastasks.tasks.application.port.in.RetrieveTaskFromTaskListUseCase;
 import ch.unisg.tapastasks.tasks.domain.Task;
+import com.fasterxml.jackson.core.JsonProcessingException;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
@@ -11,6 +13,11 @@ import org.springframework.web.server.ResponseStatusException;
 
 import java.util.Optional;
 
+/**
+ * Controller that handles HTTP GET requests for retrieving tasks. This controller implements the
+ * {@link RetrieveTaskFromTaskListUseCase} use case using the {@link RetrieveTaskFromTaskListQuery}
+ * query.
+ */
 @RestController
 public class RetrieveTaskFromTaskListWebController {
     private final RetrieveTaskFromTaskListUseCase retrieveTaskFromTaskListUseCase;
@@ -19,10 +26,17 @@ public class RetrieveTaskFromTaskListWebController {
         this.retrieveTaskFromTaskListUseCase = retrieveTaskFromTaskListUseCase;
     }
 
+    /**
+     * Retrieves a representation of task. Returns HTTP 200 OK if the request is successful with a
+     * representation of the task using the Content-Type "applicatoin/task+json".
+     *
+     * @param taskId the local identifier of the requested task (extracted from the task's URI)
+     * @return a representation of the task if the task exists
+     */
     @GetMapping(path = "/tasks/{taskId}")
     public ResponseEntity<String> retrieveTaskFromTaskList(@PathVariable("taskId") String taskId) {
-        RetrieveTaskFromTaskListQuery command = new RetrieveTaskFromTaskListQuery(new Task.TaskId(taskId));
+        RetrieveTaskFromTaskListQuery query = new RetrieveTaskFromTaskListQuery(new Task.TaskId(taskId));
-        Optional<Task> updatedTaskOpt = retrieveTaskFromTaskListUseCase.retrieveTaskFromTaskList(command);
+        Optional<Task> updatedTaskOpt = retrieveTaskFromTaskListUseCase.retrieveTaskFromTaskList(query);
 
         // Check if the task with the given identifier exists
         if (updatedTaskOpt.isEmpty()) {
@@ -30,11 +44,16 @@ public class RetrieveTaskFromTaskListWebController {
             throw new ResponseStatusException(HttpStatus.NOT_FOUND);
         }
 
+        try {
+            String taskRepresentation = TaskJsonRepresentation.serialize(updatedTaskOpt.get());
+
             // Add the content type as a response header
             HttpHeaders responseHeaders = new HttpHeaders();
-        responseHeaders.add(HttpHeaders.CONTENT_TYPE, TaskMediaType.TASK_MEDIA_TYPE);
+            responseHeaders.add(HttpHeaders.CONTENT_TYPE, TaskJsonRepresentation.MEDIA_TYPE);
 
-        return new ResponseEntity<>(TaskMediaType.serialize(updatedTaskOpt.get()), responseHeaders,
+            return new ResponseEntity<>(taskRepresentation, responseHeaders, HttpStatus.OK);
-                HttpStatus.OK);
+        } catch (JsonProcessingException e) {
+            throw new ResponseStatusException(HttpStatus.INTERNAL_SERVER_ERROR, e.getMessage());
+        }
     }
 }

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/adapter/in/web/TaskMediaType.java

@@ -1,23 +0,0 @@
-package ch.unisg.tapastasks.tasks.adapter.in.web;
-
-import ch.unisg.tapastasks.tasks.domain.Task;
-import ch.unisg.tapastasks.tasks.domain.TaskList;
-import org.json.JSONObject;
-
-final public class TaskMediaType {
-    public static final String TASK_MEDIA_TYPE = "application/json";
-
-    public static String serialize(Task task) {
-        JSONObject payload = new JSONObject();
-
-        payload.put("taskId", task.getTaskId().getValue());
-        payload.put("taskName", task.getTaskName().getValue());
-        payload.put("taskType", task.getTaskType().getValue());
-        payload.put("taskState", task.getTaskState().getValue());
-        payload.put("taskListName", TaskList.getTapasTaskList().getTaskListName().getValue());
-
-        return payload.toString();
-    }
-
-    private TaskMediaType() { }
-}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/handler/TaskAssignedHandler.java

@@ -0,0 +1,19 @@
+package ch.unisg.tapastasks.tasks.application.handler;
+
+import ch.unisg.tapastasks.tasks.application.port.in.TaskAssignedEvent;
+import ch.unisg.tapastasks.tasks.application.port.in.TaskAssignedEventHandler;
+import ch.unisg.tapastasks.tasks.domain.Task;
+import ch.unisg.tapastasks.tasks.domain.TaskList;
+import ch.unisg.tapastasks.tasks.domain.TaskNotFoundException;
+import org.springframework.stereotype.Component;
+
+@Component
+public class TaskAssignedHandler implements TaskAssignedEventHandler {
+
+    @Override
+    public Task handleTaskAssigned(TaskAssignedEvent taskAssignedEvent) throws TaskNotFoundException {
+        TaskList taskList = TaskList.getTapasTaskList();
+        return taskList.changeTaskStatusToAssigned(taskAssignedEvent.getTaskId(),
+            taskAssignedEvent.getServiceProvider());
+    }
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/handler/TaskExecutedHandler.java

@@ -0,0 +1,19 @@
+package ch.unisg.tapastasks.tasks.application.handler;
+
+import ch.unisg.tapastasks.tasks.application.port.in.TaskExecutedEvent;
+import ch.unisg.tapastasks.tasks.application.port.in.TaskExecutedEventHandler;
+import ch.unisg.tapastasks.tasks.domain.Task;
+import ch.unisg.tapastasks.tasks.domain.TaskList;
+import ch.unisg.tapastasks.tasks.domain.TaskNotFoundException;
+import org.springframework.stereotype.Component;
+
+@Component
+public class TaskExecutedHandler implements TaskExecutedEventHandler {
+
+    @Override
+    public Task handleTaskExecuted(TaskExecutedEvent taskExecutedEvent) throws TaskNotFoundException {
+        TaskList taskList = TaskList.getTapasTaskList();
+        return taskList.changeTaskStatusToExecuted(taskExecutedEvent.getTaskId(),
+            taskExecutedEvent.getServiceProvider(), taskExecutedEvent.getOutputData());
+    }
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/handler/TaskStartedHandler.java

@@ -0,0 +1,19 @@
+package ch.unisg.tapastasks.tasks.application.handler;
+
+import ch.unisg.tapastasks.tasks.application.port.in.TaskStartedEvent;
+import ch.unisg.tapastasks.tasks.application.port.in.TaskStartedEventHandler;
+import ch.unisg.tapastasks.tasks.domain.Task;
+import ch.unisg.tapastasks.tasks.domain.TaskList;
+import ch.unisg.tapastasks.tasks.domain.TaskNotFoundException;
+import org.springframework.stereotype.Component;
+
+@Component
+public class TaskStartedHandler implements TaskStartedEventHandler {
+
+    @Override
+    public Task handleTaskStarted(TaskStartedEvent taskStartedEvent) throws TaskNotFoundException {
+        TaskList taskList = TaskList.getTapasTaskList();
+        return taskList.changeTaskStatusToRunning(taskStartedEvent.getTaskId(),
+            taskStartedEvent.getServiceProvider());
+    }
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/port/in/AddNewTaskToTaskListCommand.java

@@ -1,23 +1,30 @@
 package ch.unisg.tapastasks.tasks.application.port.in;
 
 import ch.unisg.tapastasks.common.SelfValidating;
-import ch.unisg.tapastasks.tasks.domain.Task.TaskType;
+import ch.unisg.tapastasks.tasks.domain.Task;
-import ch.unisg.tapastasks.tasks.domain.Task.TaskName;
+import lombok.Getter;
 import lombok.Value;
 
 import javax.validation.constraints.NotNull;
+import java.util.Optional;
 
 @Value
 public class AddNewTaskToTaskListCommand extends SelfValidating<AddNewTaskToTaskListCommand> {
     @NotNull
-    private final TaskName taskName;
+    private final Task.TaskName taskName;
 
     @NotNull
-    private final TaskType taskType;
+    private final Task.TaskType taskType;
 
-    public AddNewTaskToTaskListCommand(TaskName taskName, TaskType taskType) {
+    @Getter
+    private final Optional<Task.OriginalTaskUri> originalTaskUri;
+
+    public AddNewTaskToTaskListCommand(Task.TaskName taskName, Task.TaskType taskType,
+            Optional<Task.OriginalTaskUri> originalTaskUri) {
         this.taskName = taskName;
         this.taskType = taskType;
+        this.originalTaskUri = originalTaskUri;
+
         this.validateSelf();
     }
 }

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/port/in/RetrieveTaskFromTaskListUseCase.java

@@ -5,5 +5,5 @@ import ch.unisg.tapastasks.tasks.domain.Task;
 import java.util.Optional;
 
 public interface RetrieveTaskFromTaskListUseCase {
-    Optional<Task> retrieveTaskFromTaskList(RetrieveTaskFromTaskListQuery command);
+    Optional<Task> retrieveTaskFromTaskList(RetrieveTaskFromTaskListQuery query);
 }

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/port/in/TaskAssignedEvent.java

@@ -0,0 +1,25 @@
+package ch.unisg.tapastasks.tasks.application.port.in;
+
+import ch.unisg.tapastasks.common.SelfValidating;
+import ch.unisg.tapastasks.tasks.domain.Task;
+import lombok.Getter;
+import lombok.Value;
+
+import javax.validation.constraints.NotNull;
+import java.util.Optional;
+
+@Value
+public class TaskAssignedEvent extends SelfValidating<TaskAssignedEvent> {
+    @NotNull
+    private final Task.TaskId taskId;
+
+    @Getter
+    private final Optional<Task.ServiceProvider> serviceProvider;
+
+    public TaskAssignedEvent(Task.TaskId taskId, Optional<Task.ServiceProvider> serviceProvider) {
+        this.taskId = taskId;
+        this.serviceProvider = serviceProvider;
+
+        this.validateSelf();
+    }
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/port/in/TaskAssignedEventHandler.java

@@ -0,0 +1,8 @@
+package ch.unisg.tapastasks.tasks.application.port.in;
+
+import ch.unisg.tapastasks.tasks.domain.Task;
+
+public interface TaskAssignedEventHandler {
+
+    Task handleTaskAssigned(TaskAssignedEvent taskStartedEvent);
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/port/in/TaskExecutedEvent.java

@@ -0,0 +1,34 @@
+package ch.unisg.tapastasks.tasks.application.port.in;
+
+import ch.unisg.tapastasks.common.SelfValidating;
+import ch.unisg.tapastasks.tasks.domain.Task.*;
+import lombok.Getter;
+import lombok.Value;
+
+import javax.validation.constraints.NotNull;
+import java.util.Optional;
+
+@Value
+public class TaskExecutedEvent extends SelfValidating<TaskExecutedEvent> {
+    @NotNull
+    private final TaskId taskId;
+
+    @Getter
+    private final Optional<ServiceProvider> serviceProvider;
+
+    @Getter
+    private final Optional<OutputData> outputData;
+
+    public TaskExecutedEvent(TaskId taskId, Optional<ServiceProvider> serviceProvider,
+            Optional<OutputData> outputData) {
+        this.taskId = taskId;
+
+        this.serviceProvider = serviceProvider;
+        this.outputData = outputData;
+
+        this.validateSelf();
+    }
+
+
+
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/port/in/TaskExecutedEventHandler.java

@@ -0,0 +1,8 @@
+package ch.unisg.tapastasks.tasks.application.port.in;
+
+import ch.unisg.tapastasks.tasks.domain.Task;
+
+public interface TaskExecutedEventHandler  {
+
+    Task handleTaskExecuted(TaskExecutedEvent taskExecutedEvent);
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/port/in/TaskStartedEvent.java

@@ -0,0 +1,28 @@
+package ch.unisg.tapastasks.tasks.application.port.in;
+
+import ch.unisg.tapastasks.common.SelfValidating;
+import ch.unisg.tapastasks.tasks.domain.Task;
+import lombok.Getter;
+import lombok.Value;
+
+import javax.validation.constraints.NotNull;
+import java.util.Optional;
+
+@Value
+public class TaskStartedEvent extends SelfValidating<TaskStartedEvent> {
+    @NotNull
+    private final Task.TaskId taskId;
+
+    @Getter
+    private final Optional<Task.ServiceProvider> serviceProvider;
+
+    public TaskStartedEvent(Task.TaskId taskId, Optional<Task.ServiceProvider> serviceProvider) {
+        this.taskId = taskId;
+        this.serviceProvider = serviceProvider;
+
+        this.validateSelf();
+    }
+
+
+
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/port/in/TaskStartedEventHandler.java

@@ -0,0 +1,8 @@
+package ch.unisg.tapastasks.tasks.application.port.in;
+
+import ch.unisg.tapastasks.tasks.domain.Task;
+
+public interface TaskStartedEventHandler {
+
+    Task handleTaskStarted(TaskStartedEvent taskStartedEvent);
+}

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/service/AddNewTaskToTaskListService.java

@@ -21,7 +21,13 @@ public class AddNewTaskToTaskListService implements AddNewTaskToTaskListUseCase
     @Override
     public Task addNewTaskToTaskList(AddNewTaskToTaskListCommand command) {
         TaskList taskList = TaskList.getTapasTaskList();
-        Task newTask = taskList.addNewTaskWithNameAndType(command.getTaskName(), command.getTaskType());
+
+        Task newTask = (command.getOriginalTaskUri().isPresent()) ?
+            // Create a delegated task that points back to the original task
+            taskList.addNewTaskWithNameAndTypeAndOriginalTaskUri(command.getTaskName(),
+                command.getTaskType(), command.getOriginalTaskUri().get())
+            // Create an original task
+            : taskList.addNewTaskWithNameAndType(command.getTaskName(), command.getTaskType());
 
         //Here we are using the application service to emit the domain event to the outside of the bounded context.
         //This event should be considered as a light-weight "integration event" to communicate with other services.

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/application/service/RetrieveTaskFromTaskListService.java

@@ -15,8 +15,8 @@ import java.util.Optional;
 @Transactional
 public class RetrieveTaskFromTaskListService implements RetrieveTaskFromTaskListUseCase {
     @Override
-    public Optional<Task> retrieveTaskFromTaskList(RetrieveTaskFromTaskListQuery command) {
+    public Optional<Task> retrieveTaskFromTaskList(RetrieveTaskFromTaskListQuery query) {
         TaskList taskList = TaskList.getTapasTaskList();
-        return taskList.retrieveTaskById(command.getTaskId());
+        return taskList.retrieveTaskById(query.getTaskId());
     }
 }

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/domain/Task.java

@@ -8,7 +8,7 @@ import java.util.UUID;
 
 /**This is a domain entity**/
 public class Task {
-    public enum State {
+    public enum Status {
         OPEN, ASSIGNED, RUNNING, EXECUTED
     }
 
@@ -22,38 +22,81 @@ public class Task {
     private final TaskType taskType;
 
     @Getter
-    private TaskState taskState;
+    private final OriginalTaskUri originalTaskUri;
+
+    @Getter @Setter
+    private TaskStatus taskStatus;
+
+    @Getter @Setter
+    private ServiceProvider provider;
+
+    @Getter @Setter
+    private InputData inputData;
+
+    @Getter @Setter
+    private OutputData outputData;
+
+    public Task(TaskName taskName, TaskType taskType, OriginalTaskUri taskUri) {
+        this.taskId = new TaskId(UUID.randomUUID().toString());
 
-    public Task(TaskName taskName, TaskType taskType) {
         this.taskName = taskName;
         this.taskType = taskType;
-        this.taskState = new TaskState(State.OPEN);
+        this.originalTaskUri = taskUri;
-        this.taskId = new TaskId(UUID.randomUUID().toString());
+
+        this.taskStatus = new TaskStatus(Status.OPEN);
+
+        this.inputData = null;
+        this.outputData = null;
     }
 
     protected static Task createTaskWithNameAndType(TaskName name, TaskType type) {
         //This is a simple debug message to see that the request has reached the right method in the core
         System.out.println("New Task: " + name.getValue() + " " + type.getValue());
-        return new Task(name,type);
+        return new Task(name, type, null);
+    }
+
+    protected static Task createTaskWithNameAndTypeAndOriginalTaskUri(TaskName name, TaskType type,
+            OriginalTaskUri originalTaskUri) {
+        return new Task(name, type, originalTaskUri);
     }
 
     @Value
     public static class TaskId {
-        private String value;
+        String value;
     }
 
     @Value
     public static class TaskName {
-        private String value;
+        String value;
-    }
-
-    @Value
-    public static class TaskState {
-        private State value;
     }
 
     @Value
     public static class TaskType {
-        private String value;
+        String value;
+    }
+
+    @Value
+    public static class OriginalTaskUri {
+        String value;
+    }
+
+    @Value
+    public static class TaskStatus {
+        Status value;
+    }
+
+    @Value
+    public static class ServiceProvider {
+        String value;
+    }
+
+    @Value
+    public static class InputData {
+        String value;
+    }
+
+    @Value
+    public static class OutputData {
+        String value;
     }
 }

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/domain/TaskList.java

@@ -3,7 +3,6 @@ package ch.unisg.tapastasks.tasks.domain;
 import lombok.Getter;
 import lombok.Value;
 
-import javax.swing.text.html.Option;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Optional;
@@ -20,7 +19,7 @@ public class TaskList {
 
     //Note: We do not care about the management of task lists, there is only one within this service
     //--> using the Singleton pattern here to make lives easy; we will later load it from a repo
-    //TODO change "tutors" to your group name ("groupx")
+    //TODO: change "tutors" to your group name ("groupx")
     private static final TaskList taskList = new TaskList(new TaskListName("tapas-tasks-tutors"));
 
     private TaskList(TaskListName taskListName) {
@@ -36,13 +35,26 @@ public class TaskList {
     //Note: Here we could add some sophisticated invariants/business rules that the aggregate root checks
     public Task addNewTaskWithNameAndType(Task.TaskName name, Task.TaskType type) {
         Task newTask = Task.createTaskWithNameAndType(name, type);
-        listOfTasks.value.add(newTask);
+        this.addNewTaskToList(newTask);
-        //This is a simple debug message to see that the task list is growing with each new request
+
-        System.out.println("Number of tasks: "+listOfTasks.value.size());
+        return newTask;
+    }
+
+    public Task addNewTaskWithNameAndTypeAndOriginalTaskUri(Task.TaskName name, Task.TaskType type,
+            Task.OriginalTaskUri originalTaskUri) {
+        Task newTask = Task.createTaskWithNameAndTypeAndOriginalTaskUri(name, type, originalTaskUri);
+        this.addNewTaskToList(newTask);
+
+        return newTask;
+    }
+
+    private void addNewTaskToList(Task newTask) {
         //Here we would also publish a domain event to other entities in the core interested in this event.
         //However, we skip this here as it makes the core even more complex (e.g., we have to implement a light-weight
         //domain event publisher and subscribers (see "Implementing Domain-Driven Design by V. Vernon, pp. 296ff).
-        return newTask;
+        listOfTasks.value.add(newTask);
+        //This is a simple debug message to see that the task list is growing with each new request
+        System.out.println("Number of tasks: " + listOfTasks.value.size());
     }
 
     public Optional<Task> retrieveTaskById(Task.TaskId id) {
@@ -55,6 +67,43 @@ public class TaskList {
         return Optional.empty();
     }
 
+    public Task changeTaskStatusToAssigned(Task.TaskId id, Optional<Task.ServiceProvider> serviceProvider)
+            throws TaskNotFoundException {
+        return changeTaskStatus(id, new Task.TaskStatus(Task.Status.ASSIGNED), serviceProvider, Optional.empty());
+    }
+
+    public Task changeTaskStatusToRunning(Task.TaskId id, Optional<Task.ServiceProvider> serviceProvider)
+            throws TaskNotFoundException {
+        return changeTaskStatus(id, new Task.TaskStatus(Task.Status.RUNNING), serviceProvider, Optional.empty());
+    }
+
+    public Task changeTaskStatusToExecuted(Task.TaskId id, Optional<Task.ServiceProvider> serviceProvider,
+            Optional<Task.OutputData> outputData) throws TaskNotFoundException {
+        return changeTaskStatus(id, new Task.TaskStatus(Task.Status.EXECUTED), serviceProvider, outputData);
+    }
+
+    private Task changeTaskStatus(Task.TaskId id, Task.TaskStatus status, Optional<Task.ServiceProvider> serviceProvider,
+            Optional<Task.OutputData> outputData) {
+        Optional<Task> taskOpt = retrieveTaskById(id);
+
+        if (taskOpt.isEmpty()) {
+            throw new TaskNotFoundException();
+        }
+
+        Task task = taskOpt.get();
+        task.setTaskStatus(status);
+
+        if (serviceProvider.isPresent()) {
+            task.setProvider(serviceProvider.get());
+        }
+
+        if (outputData.isPresent()) {
+            task.setOutputData(outputData.get());
+        }
+
+        return task;
+    }
+
     @Value
     public static class TaskListName {
         private String value;
@@ -64,5 +113,4 @@ public class TaskList {
     public static class ListOfTasks {
         private List<Task> value;
     }
-
 }

tapas-tasks/src/main/java/ch/unisg/tapastasks/tasks/domain/TaskNotFoundException.java

@@ -0,0 +1,3 @@
+package ch.unisg.tapastasks.tasks.domain;
+
+public class TaskNotFoundException extends RuntimeException { }

tapas-tasks/src/main/resources/application.properties

@@ -1 +1,2 @@
 server.port=8081
+baseuri=https://tapas-tasks.86-119-34-23.nip.io/