feat: add private message

app/src/main/java/clientserver/server/MessageProcessor.java

@@ -1,7 +1,6 @@
 package clientserver.server;
 
 import clientserver.client.Client;
-import java.net.DatagramPacket;
 import java.net.DatagramSocket;
 
 public class MessageProcessor {
@@ -25,11 +24,84 @@ public class MessageProcessor {
             return;
         }
 
-        if (message.equals("/list")) {
-            handleListCommand();
-        } else if (message.equals("DISCONNECT")) {
-            handleDisconnect();
+        if (message.startsWith("/msg ")) {
+            handlePrivateMessage(message);
+            return;
         }
+
+        switch (message) {
+            case "/list":
+                handleListCommand();
+                break;
+            case "/help":
+                handleHelpCommand();
+                break;
+            case "/msg":
+                handleMsgCommand();
+                break;
+            case "/disconnect":
+                handleDisconnect();
+                break;
+        }
+    }
+
+    private void handlePrivateMessage(String message) {
+        String[] parts = message.split(" ", 3);
+        if (parts.length < 3) {
+            handleMsgCommand();
+            return;
+        }
+
+        String targetPseudo = parts[1];
+        String messageContent = parts[2];
+
+        ClientHandler targetHandler = Server.getClientHandler(targetPseudo);
+
+        if (targetHandler == null) {
+            Server.sendMessage(
+                clientHandlerSocket,
+                "> User " + targetPseudo + " not found",
+                client.getAddress(),
+                client.getPort()
+            );
+            return;
+        }
+
+        // Send private message to target
+        Client targetClient = targetHandler.getClient();
+        Server.sendMessage(
+            clientHandlerSocket,
+            "> " +
+            client.getPseudo() +
+            " -> " +
+            targetClient.getPseudo() +
+            ": " +
+            messageContent,
+            targetClient.getAddress(),
+            targetClient.getPort()
+        );
+
+        // Send confirmation to sender
+        Server.sendMessage(
+            clientHandlerSocket,
+            "> " +
+            client.getPseudo() +
+            " -> " +
+            targetClient.getPseudo() +
+            ": " +
+            messageContent,
+            client.getAddress(),
+            client.getPort()
+        );
+    }
+
+    private void handleMsgCommand() {
+        Server.sendMessage(
+            clientHandlerSocket,
+            "> /msg <target> <message> : send a message to a client",
+            client.getAddress(),
+            client.getPort()
+        );
     }
 
     private void handleListCommand() {
@@ -41,6 +113,17 @@ public class MessageProcessor {
         );
     }
 
+    private void handleHelpCommand() {
+        Server.sendMessage(
+            clientHandlerSocket,
+            "> /list : list all connected clients" +
+            "\n> /msg <target> <message> : send a message to a client" +
+            "\n> /disconnect : disconnect from the server",
+            client.getAddress(),
+            client.getPort()
+        );
+    }
+
     private void handleDisconnect() {
         System.out.println(
             "Client deconnection : " + ClientHandler.prettyPrint(client)