first commit

week2_TinsaeGhilay/Task2/.gitignore

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+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+.kotlin
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store

week2_TinsaeGhilay/Task2/.idea/.gitignore

@@ -0,0 +1,8 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml

week2_TinsaeGhilay/Task2/.idea/encodings.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Encoding">
+    <file url="file://$PROJECT_DIR$/src/main/java" charset="UTF-8" />
+    <file url="file://$PROJECT_DIR$/src/main/resources" charset="UTF-8" />
+  </component>
+</project>

week2_TinsaeGhilay/Task2/.idea/misc.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="KubernetesApiProvider"><![CDATA[{}]]></component>
+  <component name="MavenProjectsManager">
+    <option name="originalFiles">
+      <list>
+        <option value="$PROJECT_DIR$/pom.xml" />
+      </list>
+    </option>
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="21 (3)" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>

week2_TinsaeGhilay/Task2/.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>

week2_TinsaeGhilay/Task2/pom.xml

@@ -0,0 +1,34 @@
+<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>org.distributed</groupId>
+    <artifactId>Task2</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.activemq</groupId>
+            <artifactId>activemq-all</artifactId>
+            <version>5.18.4</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.logging.log4j</groupId>
+            <artifactId>log4j-core</artifactId>
+            <version>2.23.1</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.apache.logging.log4j</groupId>
+            <artifactId>log4j-slf4j2-impl</artifactId>
+            <version>2.23.1</version>
+        </dependency>
+    </dependencies>
+</project>

week2_TinsaeGhilay/Task2/src/main/java/org/distributed/ChatHandler.java

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+package org.distributed;
+/**
+ * ChatHandler.java
+ * by Tinsae Ghilay
+ * Handles chat session, message sending and receiving using JMS queues.
+ * Uses ActiveMQ as the message broker.
+ * done for Distributed Systems Course - Week 2 Task 2
+ * Date: June 2024
+ */
+
+import java.util.Scanner;
+import javax.jms.*;
+import org.apache.activemq.ActiveMQConnectionFactory;
+
+// ChatHandler class to manage chat sessions
+public class ChatHandler {
+
+    // chatting ids
+    private String userId, corespondent;
+    private Connection connection;
+    private Session session;
+    int status = 0; // 0: offline, 1: online
+
+    // Initialize connection and session
+    public void initializeSession() throws JMSException {
+        String BROKER_URL = "tcp://localhost:61616";
+        ConnectionFactory factory = new ActiveMQConnectionFactory(BROKER_URL);
+        this.connection = factory.createConnection();
+        this.connection.start();
+        this.session = this.connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
+    }
+
+    // Start continuous conversation with multiple receivers
+    public void startConversation(Scanner sc) throws JMSException {
+
+        // Initialize all producers and consumers
+        Thread t = setupReceiver();
+
+        // Continuous input loop
+        try {
+            while (sc.hasNextLine()) {
+                String line = sc.nextLine();
+
+                // Send message to receiver
+                sendMessage(createProducer(), line);
+
+                // Exit condition
+                if (line.equalsIgnoreCase("exit")) {
+                    System.out.println("Exiting conversation...");
+                    break;
+                }
+            }
+        } catch (Exception e) {
+            System.err.println("Error in continuous conversation: " + e.getMessage());
+        } finally {
+            t.interrupt();
+        }
+    }
+
+    // Setup producer and consumer for a receiver
+    private Thread setupReceiver() throws JMSException {
+
+        MessageConsumer consumer = createConsumer();
+
+        return getThread(consumer);
+    }
+
+    // Create producer queue for sending messages
+    private MessageProducer createProducer() throws JMSException {
+        String from = "queue_" + userId;
+        Queue prod = session.createQueue(from);
+        return session.createProducer(prod);
+    }
+
+    // Create consumer queue for receiving messages
+    private MessageConsumer createConsumer() throws JMSException {
+        String to = "queue_" + getCorespondent();
+        Queue cons = session.createQueue(to);
+        return session.createConsumer(cons);
+    }
+
+    // Send a message to the producer
+    private void sendMessage(MessageProducer producer, String line) throws JMSException {
+        TextMessage m = session.createTextMessage(line);
+        m.setStringProperty("sender", userId);
+        producer.send(m);
+    }
+
+    // Close connection and session
+    public void closeSession() throws JMSException {
+        if (session != null) {
+            session.close();
+        }
+        if (connection != null) {
+            connection.close();
+        }
+    }
+
+    // Returns a thread object to handle receiving messages
+    private Thread getThread(MessageConsumer consumer) {
+        Thread receivingThread = new Thread(() -> {
+            try {
+                // continously listen for messages
+                while (!Thread.currentThread().isInterrupted()) {
+                    Message msg = consumer.receive(300);
+                    if (msg instanceof TextMessage tm) {
+
+                        // Status handling for online/offline
+                        if(tm.getText().isBlank() || tm.getText().isEmpty()) {
+                            setStatus(1);
+                            continue;
+                        }
+                      
+                        // Exit condition because correspondent went offline
+                        if(tm.getText().equalsIgnoreCase("exit")) { 
+                            setStatus(0);
+                            continue;
+                        }
+
+                        // Display received message
+                        String sender = tm.getStringProperty("sender");
+                        String body = tm.getText();
+                        System.out.println("[" + sender + "]: " + body);
+                    }
+                }
+            } catch (javax.jms.JMSException e) {
+                // Silently handle interruption - normal shutdown behavior
+                if (!Thread.currentThread().isInterrupted()) {
+                    System.err.println("Error receiving message: " + e.getMessage());
+                }
+            }
+        });
+        receivingThread.start();
+        // we are returning this so we can interrupt it later
+        return receivingThread;
+    }
+
+    // Prompt for user ID
+    public void promptForUser(Scanner sc){
+
+        System.out.print("Enter your user ID: ");
+        setUserId(prompt(sc));
+        // Instructions
+        System.out.print("Welcome "+getUserId());
+        System.out.println(" -> Type 'exit' to quit.");
+    }
+
+    // Prompt for correspondent ID
+    public void promptForCorespondent(Scanner sc){
+
+        System.out.print("Who do you want to chat with? ");
+        setCorespondent(prompt(sc));
+        System.out.println("You can chat with: " + getCorespondent());
+    }
+
+    // Generic prompt method prompts for whatever we need
+    private String prompt(Scanner sc) {
+
+        String user = "";
+
+        while (user.isEmpty()) {
+            try {
+                user = sc.next();
+
+            } catch (Exception e) {
+                System.err.println("Error reading correspondent ID: " + e.getMessage());
+                return null;
+            }
+        }
+        return user;
+    }
+
+    // Setters and getters
+    // user
+    public void setUserId(String userId) {
+        this.userId = userId;
+    }
+
+    public String getUserId() {
+        return userId;
+    }
+
+    // correspondent
+    public String getCorespondent() {
+        return corespondent;
+    }
+
+    public void setCorespondent(String corespondent) {
+        this.corespondent = corespondent;
+    }
+
+    // update status of correspondent and print status message
+    private void setStatus(int status) {
+
+        // just incase of duplicate status messages, if status is same, return
+        if(this.status == status) {
+            return; 
+        }
+        this.status = status;
+        if(status == 0) {
+            System.out.println(getCorespondent()+" is now offline.");
+        } else {
+            System.out.println(getCorespondent()+" is now online.");
+        }
+    }
+}

week2_TinsaeGhilay/Task2/src/main/java/org/distributed/Main.java

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+package org.distributed;
+/**
+ * Main.java
+ * by Tinsae Ghilay
+ * Entry point for the chat application.
+ * done for Distributed Systems Course - Week 2 Task 2
+ * Date: June 2024
+ */
+
+import java.util.Scanner;
+public class Main {
+
+    // entry point
+    public static void main(String[] args) throws Exception {
+
+        // create a client
+        ChatHandler handler = new ChatHandler();
+
+        // init connection and session session
+        handler.initializeSession();
+
+        // create scanner for user input
+        Scanner sc = new Scanner(System.in);
+
+        // log in user
+        handler.promptForUser(sc);
+
+        // specify correspondent
+        handler.promptForCorespondent(sc);
+
+        // start conversation
+        handler.startConversation(sc);
+
+        // close session after all receivers are processed
+        handler.closeSession();
+    }
+}

week2_TinsaeGhilay/Task3/.gitignore

@@ -0,0 +1,39 @@
+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+.kotlin
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store

week2_TinsaeGhilay/Task3/.idea/.gitignore

@@ -0,0 +1,8 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml

week2_TinsaeGhilay/Task3/.idea/encodings.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Encoding">
+    <file url="file://$PROJECT_DIR$/src/main/java" charset="UTF-8" />
+    <file url="file://$PROJECT_DIR$/src/main/resources" charset="UTF-8" />
+  </component>
+</project>

week2_TinsaeGhilay/Task3/.idea/inspectionProfiles/Project_Default.xml

@@ -0,0 +1,8 @@
+<component name="InspectionProjectProfileManager">
+  <profile version="1.0">
+    <option name="myName" value="Project Default" />
+    <inspection_tool class="AutoCloseableResource" enabled="true" level="WARNING" enabled_by_default="true">
+      <option name="METHOD_MATCHER_CONFIG" value="java.util.Formatter,format,java.io.Writer,append,com.google.common.base.Preconditions,checkNotNull,org.hibernate.Session,close,java.io.PrintWriter,printf,java.io.PrintStream,printf,java.lang.foreign.Arena,ofAuto,java.lang.foreign.Arena,global,java.util.Map,remove" />
+    </inspection_tool>
+  </profile>
+</component>

week2_TinsaeGhilay/Task3/.idea/misc.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="KubernetesApiProvider"><![CDATA[{}]]></component>
+  <component name="MavenProjectsManager">
+    <option name="originalFiles">
+      <list>
+        <option value="$PROJECT_DIR$/pom.xml" />
+      </list>
+    </option>
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="21 (2)" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>

week2_TinsaeGhilay/Task3/.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>

week2_TinsaeGhilay/Task3/pom.xml

@@ -0,0 +1,34 @@
+<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>org.distributed</groupId>
+    <artifactId>Task3</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.activemq</groupId>
+            <artifactId>activemq-all</artifactId>
+            <version>5.18.4</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.logging.log4j</groupId>
+            <artifactId>log4j-core</artifactId>
+            <version>2.23.1</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.logging.log4j</groupId>
+            <artifactId>log4j-slf4j2-impl</artifactId>
+            <version>2.23.1</version>
+        </dependency>
+    </dependencies>
+
+</project>

week2_TinsaeGhilay/Task3/src/main/java/org/distributed/ChatHandler.java

@@ -0,0 +1,396 @@
+package org.distributed;
+import java.util.Map;
+import java.util.Scanner;
+import java.util.concurrent.ConcurrentHashMap;
+import javax.jms.*;
+import org.apache.activemq.ActiveMQConnectionFactory;
+
+public class ChatHandler {
+
+    private String userId, corespondent;
+    private Connection connection;
+    private Session /*session,*/ senderSession, receiverSession;
+    private int status = 0; // 0: offline, 1: online
+    private final Map<String, MessageProducer> blocked = new ConcurrentHashMap<>();
+    private final String TAG = "Task3_queue_";
+    private final String BROKER_URL = "tcp://localhost:61616";
+    /**
+     * Initialize JMS session
+     * @throws JMSException
+     */
+    public void initializeSession() throws JMSException {
+        ConnectionFactory factory = new ActiveMQConnectionFactory(BROKER_URL);
+        this.connection = factory.createConnection();
+        this.connection.start();
+        //this.session = this.connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
+        this.senderSession = this.connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
+        this.receiverSession = this.connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
+    }
+
+    /**
+     * Start conversation loop
+     * @param sc
+     * @throws JMSException
+     */
+    public void startConversation(Scanner sc) throws JMSException {
+
+        // init receiving thread
+        Thread t = setupReceiver(userId);
+
+        // Continuous input loop
+        try {
+            while (sc.hasNextLine()){
+
+                // handle user input and send messages
+                // or if exit command, break loop
+                if(!respond(sc)){ 
+                    break;
+                }
+            }
+        } catch (Exception e) {
+            System.err.println("Error in continuous conversation: " + e.getMessage());
+        } finally {
+            t.interrupt();
+        }
+    }
+
+    /**
+     * Handle user input and send messages
+     * @param sc
+     * @throws JMSException
+     */
+    private boolean respond(Scanner sc) throws JMSException {
+        String line = sc.nextLine();
+
+        // commands to block or unblock contact
+        if(line.startsWith("-")){
+            delegateBlockingManagement(sc,line);
+            //return true;
+        }
+
+        if (line.equalsIgnoreCase("exit")) {
+            System.out.println("Exiting conversation...");
+            //return false;
+        }
+
+        // Send message to receiver
+        sendMessage(createProducer(corespondent), line);
+        return !line.equalsIgnoreCase("exit");//true;
+    }
+
+
+    /**
+     * Delegate blocking and unblocking management
+     * @param sc
+     * @param line
+     */
+    private void delegateBlockingManagement(Scanner sc, String line) {
+
+        // block command is -b followed by contact id
+        if(line.startsWith("-b")){
+            blockContact(line);
+            promptForCorespondent(sc);
+        }
+
+        // unblock command is -u followed by contact id
+        if(line.startsWith("-u")){
+            String contact = unBlockContact(line);
+            System.out.println("do you want to chat with: " + contact+" yes or no");
+            while(true){
+                String answer = sc.nextLine();
+                if(answer.equalsIgnoreCase("yes")){
+                    setCorespondent(contact);
+                    break;
+                } else if(answer.equalsIgnoreCase("no")){
+                    promptForCorespondent(sc);
+                    break;
+                } else {
+                    System.out.println("please answer with yes or no");
+                }
+            }
+        }
+    }
+
+    // Setup producer and consumer for a receiver
+    private Thread setupReceiver(String receiver) throws JMSException {
+        MessageConsumer contact = createConsumer();
+
+        // add consumer to contacts map
+        //contacts.put(receiver, contact);
+        return getThread(contact);
+    }
+
+    /**
+     * Create a producer for a given contact ID so we can send messages
+     * @param id
+     * @return MessageProducer
+     * @throws JMSException
+     */
+    private MessageProducer createProducer(String id) throws JMSException {
+        String from = TAG + id;
+        Queue prod = senderSession.createQueue(from);
+        return senderSession.createProducer(prod);
+    }
+
+    /**
+     * Block a contact
+     * @param command
+     */
+    private void blockContact(String command) {
+        // remove the command part to get the contact id
+        String contact = command.replace("-b", "").trim();
+        try {
+            MessageProducer ignored = createProducer(contact);
+            // remove from contacts map
+            // and close his ass
+            if(ignored != null){
+                ignored.close();
+                blocked.put(contact, ignored);
+                System.out.println(contact + " has been blocked.");
+            }
+        } catch (JMSException e) {
+            System.err.println("Error unblocking consumer: " + e.getMessage());
+        }
+    }
+
+
+    /**
+     * Unblock a contact
+     * @param command
+     * @return contact id
+     */
+    private String unBlockContact(String command) {
+
+        String contact = command.replace("-u", "").trim();
+
+        
+        try {
+            // unblock by removing his ass from blocklist
+            blocked.remove(contact);
+            // retun contact name for further handling
+            return contact;
+
+        } catch (Exception e) {
+            System.err.println("Error blocking consumer: " + e.getMessage());
+            return null;
+        }
+    }
+
+    /**
+     * Subscribe to topics meant for this user
+     * @return MessageConsumer
+     * @throws JMSException
+     */
+    private MessageConsumer createConsumer() throws JMSException {
+        String to = TAG + userId;
+        Queue cons = receiverSession.createQueue(to);
+        return receiverSession.createConsumer(cons);
+    }
+
+    /**
+     * Send a messag
+     * @param producer
+     * @param line
+     * @throws JMSException
+     */
+    private void sendMessage(MessageProducer producer, String line) throws JMSException {
+
+        TextMessage m = senderSession.createTextMessage(line);
+        // add sender identity to message
+        m.setStringProperty("sender", userId);
+        producer.send(m);
+    }
+
+    /**
+     * Close session and connection
+     * @throws JMSException
+     */
+    public void closeSession() throws JMSException {
+        if (senderSession != null) {
+            senderSession.close();
+        }
+        if( receiverSession != null) {
+            receiverSession.close();
+        }
+        if (connection != null) {
+            connection.close();
+        }
+    }
+
+    /**
+     * Returns a thread object to handle receiving messages
+     * @param consumer
+     * @return Thread
+     */
+    private Thread getThread(MessageConsumer consumer) {
+
+        Thread receivingThread = new Thread(() -> {
+            try {
+
+                while (!Thread.currentThread().isInterrupted()) {
+
+                    // receive message with timeout
+                    Message msg = consumer.receive(100); // 100ms timeout
+                    if (msg instanceof TextMessage tm) {
+                        // handle received message
+                        String sender = tm.getStringProperty("sender");
+
+                        // display message if sender is not blocked
+                        if (!isBlocked(sender)) {
+                            String body = tm.getText();
+                            displayMessage(sender, body);
+                        }
+                        
+                    }
+                }
+            } catch (javax.jms.JMSException e) {
+                // Silently handle interruption - normal shutdown behavior
+                if (!Thread.currentThread().isInterrupted()) {
+                    System.err.println("Error receiving message: " + e.getMessage());
+                }
+            }
+        });
+
+        
+        receivingThread.start();
+        // we are returning this so we can interrupt it later
+        return receivingThread;
+    }
+
+
+    /**
+     * Display received message
+     * Checks if sender is blocked
+     * checks if message is empty for status update
+     * checks for exit condition
+     * @param tm
+     * @throws JMSException
+     */
+
+    private void displayMessage(String sender, String body) {
+        
+        
+        // Exit condition because correspondent went offline
+        if(body.equalsIgnoreCase("exit")) { 
+            setStatus(0);
+            return;
+        }
+
+        // display only if not empty
+        if(!body.isBlank() || !body.isEmpty()) {
+            // Status handling for online/offline
+            System.out.println("[" + sender + "]: " + body);
+        }
+        setStatus(1);
+
+    }
+
+    /**
+     * Check if sender is blocked
+     * if sender is blocked, print info message
+     * @param sender
+     * @return
+     */
+    private boolean isBlocked(String sender) {
+        boolean isBlocked = blocked.containsKey(sender);
+        if(isBlocked){
+            System.out.println(" >> Message from '"+sender+"' ignored. because user is blocked.");
+        }
+        return isBlocked;
+    }
+
+    /**
+     * Prompt for user ID
+     * @param sc
+     */
+    public void promptForUser(Scanner sc){
+
+        System.out.print("Enter your user ID: ");
+        //userId = prompt(sc);
+        setUserId(prompt(sc));
+        // Instructions
+        System.out.print("Welcome "+getUserId());
+        System.out.println(" -> Type 'exit' to quit.");
+    }
+
+    /**
+     * Prompt for correspondent ID
+     * @param sc
+     */
+    public void promptForCorespondent(Scanner sc){
+
+        System.out.print("Who do you want to chat with? ");
+        String contact = prompt(sc);
+        setCorespondent(contact);
+        // check if contact is blocked
+        if(blocked.containsKey(contact)){
+            System.out.println(contact + " is currently blocked. Unblock to chat.");
+            return;
+        }
+    }
+
+    /**
+     * Generic prompt method prompts for whatever we need
+     * @param sc Scanner object
+     * @return String
+     */
+    private String prompt(Scanner sc) {
+
+        String user = "";
+
+        while (user.isEmpty()) {
+            try {
+                user = sc.next();
+
+            } catch (Exception e) {
+                System.err.println("Error reading correspondent ID: " + e.getMessage());
+                return null;
+            }
+        }
+        return user;
+    }
+
+    // Setters and getters
+    // user
+    public void setUserId(String userId) {
+        this.userId = userId;
+    }
+
+    public String getUserId() {
+        return userId;
+    }
+
+    // correspondent
+    public String getCorespondent() {
+        return corespondent;
+    }
+
+    public void setCorespondent(String corespondent) {
+        this.corespondent = corespondent;
+        System.out.println("You can chat with: " + corespondent);
+        // reset old status when new corepondent is set
+        setStatus(0);
+    }
+
+    /**
+     * Updates corespondents status
+     * @param status
+     */
+    private void setStatus(int status) {
+
+        // just in case of duplicate status messages, if status is same, return
+        if(this.status == status) {
+            return; 
+        }
+
+        // update status
+        this.status = status;
+
+        // and print accordingly
+        if(status == 0) {
+            System.out.println(getCorespondent()+" is now offline.");
+        } else {
+            System.out.println(getCorespondent()+" is now online.");
+        }
+    }
+}

week2_TinsaeGhilay/Task3/src/main/java/org/distributed/Main.java

@@ -0,0 +1,29 @@
+package org.distributed;
+import java.util.Scanner;
+public class Main {
+
+    // entry point
+    public static void main(String[] args) throws Exception {
+
+        // create a client
+        ChatHandler handler = new ChatHandler();
+
+        // init session
+        handler.initializeSession();
+
+        // create scanner for user input
+        Scanner sc = new Scanner(System.in);
+
+        // log in user
+        handler.promptForUser(sc);
+
+        // specify correspondent
+        handler.promptForCorespondent(sc);
+
+        // start conversation
+        handler.startConversation(sc);
+
+        // close session after all receivers are processed
+        handler.closeSession();
+    }
+}