Fix: Sent chat messages with current username at send time

Feat: Auto-cleanup lobbies when game finishes

See merge request cs108-fs26/Gruppe-13!129

src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/ClientApp.java

@@ -39,6 +39,10 @@ public class ClientApp {
         return sharedUsername;
     }
 
+    public static void updateSharedUsername(String username) {
+        setSharedUsername(username != null && !username.isBlank() ? username.trim() : null);
+    }
+
     private static void setSharedUsername(String username) {
         sharedUsername = username;
         LOGGER.info("sharedUsername set to '{}'", getSharedUsername());

src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/chat/ChatController.java

@@ -1,15 +1,20 @@
 package ch.unibas.dmi.dbis.cs108.casono.client.chat;
 
+import ch.unibas.dmi.dbis.cs108.casono.client.ClientApp;
 import ch.unibas.dmi.dbis.cs108.casono.client.network.ChatClient;
 import ch.unibas.dmi.dbis.cs108.casono.client.network.ClientService;
 import ch.unibas.dmi.dbis.cs108.casono.client.ui.chatui.ChatBoxController;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.command.parsing.RequestParameter;
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.Timer;
 import java.util.TimerTask;
 import java.util.WeakHashMap;
+import java.util.function.Consumer;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.jspecify.annotations.Nullable;
@@ -24,7 +29,7 @@ public class ChatController {
     private static final Map<ClientService, ChatController> ACTIVE_CONTROLLERS =
             new WeakHashMap<>();
 
-    private final String username;
+    private volatile String username;
 
     private final ClientService clientService;
 
@@ -37,6 +42,7 @@ public class ChatController {
     private final ChatBoxController chatBoxController;
     private int lobbyId = -1;
     private final Timer timer;
+    private final Consumer<List<String>> serverEventListener;
 
     public record ChatKey(ChatType type, @Nullable String targetUser) {
         public ChatKey(ChatType type) {
@@ -71,8 +77,10 @@ public class ChatController {
         localUserList = new ArrayList<>();
         this.chatBoxController = new ChatBoxController(username, this);
         this.logger = LogManager.getLogger(ChatController.class);
+        this.serverEventListener = this::handleServerEvent;
 
         registerAsActiveController(clientService);
+        clientService.addEventListener(serverEventListener);
 
         this.timer = new Timer(true);
         timer.schedule(
@@ -131,6 +139,7 @@ public class ChatController {
      * <p>All Messages get added to a particular {@link ChatModel}, if the checks passed.
      */
     public void receiveMessage() {
+        String currentUsername = getCurrentUsername();
         List<Message> newMessages = chatClient.getMessages();
         if (!newMessages.isEmpty()) {
             for (Message msg : newMessages) {
@@ -146,16 +155,17 @@ public class ChatController {
                                             (_key) ->
                                                     new ChatModel(
                                                             ChatType.LOBBY,
-                                                            username,
+                                                            currentUsername,
                                                             msg.lobbyId,
                                                             null))
                                     .addMessage(msg);
                         }
                         break;
                     case ChatType.WHISPER:
-                        if (msg.target.equals(username) || msg.sender.equals(username)) {
+                        if (msg.target.equals(currentUsername)
+                                || msg.sender.equals(currentUsername)) {
                             ChatKey key;
-                            if (msg.target.equals(username)) {
+                            if (msg.target.equals(currentUsername)) {
                                 key = new ChatKey(ChatType.WHISPER, msg.sender);
                             } else {
                                 key = new ChatKey(ChatType.WHISPER, msg.target);
@@ -166,7 +176,7 @@ public class ChatController {
                                 ChatModel chatModel =
                                         new ChatModel(
                                                 ChatType.WHISPER,
-                                                username,
+                                                currentUsername,
                                                 lobbyId,
                                                 key.targetUser());
                                 chatBoxController.addWhisperChat(key.targetUser(), chatModel);
@@ -203,13 +213,29 @@ public class ChatController {
      */
     public synchronized void checkWhisperUsers() {
         List<String> users = chatClient.getUsers();
-        logger.info(users);
-        if (!users.isEmpty()) {
+        Set<String> remoteUsers = new HashSet<>();
+        String currentUsername = getCurrentUsername();
+
         for (String user : users) {
-                String value = user.split("\\=")[1];
-                logger.info(value);
-                addWhisperUser(value);
+            if (user == null || !user.contains("=")) {
+                continue;
             }
+            String value = user.split("\\=", 2)[1].trim();
+            if (value.isBlank() || value.equals(currentUsername)) {
+                continue;
+            }
+            remoteUsers.add(value);
+        }
+
+        for (String known : new ArrayList<>(localUserList)) {
+            if (!remoteUsers.contains(known)) {
+                localUserList.remove(known);
+                chatBoxController.removeWhisperUser(known);
+            }
+        }
+
+        for (String remote : remoteUsers) {
+            addWhisperUser(remote);
         }
     }
 
@@ -222,16 +248,110 @@ public class ChatController {
         if (user == null || user.isBlank()) {
             return;
         }
-        if (!(localUserList.contains(user) || user.equals(username))) {
+        if (!(localUserList.contains(user) || user.equals(getCurrentUsername()))) {
             localUserList.add(user);
             logger.info("adding new whisper user");
             chatBoxController.addWhisperUser(user);
         }
     }
 
+    public synchronized void updateUsername(String newUsername) {
+        if (newUsername == null || newUsername.isBlank()) {
+            return;
+        }
+        String oldUsername = this.username;
+        this.username = newUsername.trim();
+        chatBoxController.setUsername(this.username);
+
+        if (oldUsername != null && !oldUsername.equals(this.username)) {
+            localUserList.remove(oldUsername);
+            chatBoxController.removeWhisperUser(oldUsername);
+        }
+    }
+
+    private void handleServerEvent(List<String> lines) {
+        if (lines == null || lines.isEmpty()) {
+            return;
+        }
+
+        List<RequestParameter> params;
+        try {
+            params = ClientService.convertToRequestParameters(lines);
+        } catch (RuntimeException e) {
+            return;
+        }
+        String event = null;
+        String oldUsername = null;
+        String newUsername = null;
+
+        for (RequestParameter p : params) {
+            if ("EVENT".equalsIgnoreCase(p.key())) {
+                event = p.value();
+            } else if ("OLD_USERNAME".equalsIgnoreCase(p.key())) {
+                oldUsername = p.value();
+            } else if ("NEW_USERNAME".equalsIgnoreCase(p.key())) {
+                newUsername = p.value();
+            }
+        }
+
+        if (!"USERNAME_CHANGED".equalsIgnoreCase(event)) {
+            return;
+        }
+
+        applyUsernameMigration(oldUsername, newUsername);
+    }
+
+    private synchronized void applyUsernameMigration(String oldUsername, String newUsername) {
+        if (oldUsername == null
+                || newUsername == null
+                || oldUsername.isBlank()
+                || newUsername.isBlank()
+                || oldUsername.equals(newUsername)) {
+            return;
+        }
+
+        String currentUsername = getCurrentUsername();
+        if (oldUsername.equals(currentUsername)) {
+            updateUsername(newUsername);
+        }
+
+        ChatKey oldKey = new ChatKey(ChatType.WHISPER, oldUsername);
+        ChatKey newKey = new ChatKey(ChatType.WHISPER, newUsername);
+
+        ChatModel oldModel = chatModelMap.remove(oldKey);
+        ChatModel existingNewModel = chatModelMap.get(newKey);
+        if (oldModel != null) {
+            oldModel.setTarget(newUsername);
+            if (existingNewModel == null) {
+                chatModelMap.put(newKey, oldModel);
+            } else {
+                // Merge possible parallel history into the already existing new-key model.
+                for (Message msg : oldModel.messages) {
+                    existingNewModel.addMessage(msg);
+                }
+            }
+            chatBoxController.renameWhisperUser(oldUsername, newUsername);
+        }
+
+        localUserList.remove(oldUsername);
+        chatBoxController.removeWhisperUser(oldUsername);
+        if (!newUsername.equals(getCurrentUsername())) {
+            addWhisperUser(newUsername);
+        }
+    }
+
+    public String getCurrentUsername() {
+        String shared = ClientApp.getSharedUsername();
+        if (shared != null && !shared.isBlank()) {
+            return shared.trim();
+        }
+        return username;
+    }
+
     /** Stops polling background tasks for this chat controller instance. */
     public void shutdown() {
         timer.cancel();
+        clientService.removeEventListener(serverEventListener);
         synchronized (ACTIVE_CONTROLLERS) {
             if (ACTIVE_CONTROLLERS.get(clientService) == this) {
                 ACTIVE_CONTROLLERS.remove(clientService);

src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/chat/ChatModel.java

@@ -22,7 +22,7 @@ public class ChatModel {
     public final String username;
 
     /** The person to send the message to If the chat is a whisper chat */
-    private final String target;
+    private String target;
 
     private final IntegerProperty count;
 
@@ -82,4 +82,8 @@ public class ChatModel {
     public String getTarget() {
         return target;
     }
+
+    public void setTarget(String target) {
+        this.target = target;
+    }
 }

src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/network/LobbyClient.java

@@ -131,6 +131,29 @@ public class LobbyClient {
         return new LoginResult(assigned, id);
     }
 
+    /**
+     * Changes the username for the currently logged-in session.
+     *
+     * @param newUsername desired new username
+     * @return a {@link LoginResult} containing assigned username and id as returned by the server
+     */
+    public LoginResult changeUsername(String newUsername) {
+        List<String> lines = client.processCommand("CHANGE_USERNAME USERNAME=" + newUsername);
+
+        List<RequestParameter> params = ClientService.convertToRequestParameters(lines);
+
+        String assigned = newUsername;
+        String id = null;
+        for (RequestParameter p : params) {
+            if ("USERNAME".equalsIgnoreCase(p.key())) {
+                assigned = p.value();
+            } else if ("ID".equalsIgnoreCase(p.key())) {
+                id = p.value();
+            }
+        }
+        return new LoginResult(assigned, id);
+    }
+
     /**
      * Request the server for the list of available lobbies.
      *

src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/ui/chatui/ChatBoxController.java

@@ -60,6 +60,12 @@ public class ChatBoxController {
         usernameTabMap = new HashMap<>();
     }
 
+    public void setUsername(String username) {
+        if (username != null && !username.isBlank()) {
+            this.username = username.trim();
+        }
+    }
+
     /**
      * Initializes the chat interface by creating the global chat model and adding the corresponding
      * "GLOBAL" tab to the interface. It also registers the global chat in the {@link
@@ -84,6 +90,11 @@ public class ChatBoxController {
     public void addWhisperUser(String targetUserName) {
         Platform.runLater(
                 () -> {
+                    for (MenuItem existing : addWhisperChatButton.getItems()) {
+                        if (targetUserName.equals(existing.getText())) {
+                            return;
+                        }
+                    }
                     MenuItem menuItem = new MenuItem(targetUserName);
                     addWhisperChatButton.getItems().add(menuItem);
                     menuItem.setOnAction(
@@ -98,6 +109,54 @@ public class ChatBoxController {
                 });
     }
 
+    public void removeWhisperUser(String targetUserName) {
+        Platform.runLater(
+                () ->
+                        addWhisperChatButton
+                                .getItems()
+                                .removeIf(item -> targetUserName.equals(item.getText())));
+    }
+
+    public void renameWhisperUser(String oldUsername, String newUsername) {
+        if (oldUsername == null
+                || newUsername == null
+                || oldUsername.isBlank()
+                || newUsername.isBlank()
+                || oldUsername.equals(newUsername)) {
+            return;
+        }
+
+        Platform.runLater(
+                () -> {
+                    for (MenuItem item : addWhisperChatButton.getItems()) {
+                        if (oldUsername.equals(item.getText())) {
+                            item.setText(newUsername);
+                            item.setOnAction(
+                                    event ->
+                                            addWhisperChat(
+                                                    newUsername,
+                                                    new ChatModel(
+                                                            ChatType.WHISPER,
+                                                            username,
+                                                            -1,
+                                                            newUsername)));
+                            break;
+                        }
+                    }
+
+                    Tab tab = usernameTabMap.remove(oldUsername);
+                    if (tab != null) {
+                        tab.setText(newUsername);
+                        usernameTabMap.put(newUsername, tab);
+                    }
+
+                    int idx = activeWhisperChats.indexOf(oldUsername);
+                    if (idx >= 0) {
+                        activeWhisperChats.set(idx, newUsername);
+                    }
+                });
+    }
+
     /**
      * Creates a new private (whisper) chat model for a specific target user, registers it within
      * the chat system, and opens a new chat tab.

src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/ui/chatui/ChatViewController.java

@@ -68,11 +68,12 @@ public class ChatViewController implements Initializable {
         String message = inputField.getText().trim();
         if (!message.isEmpty()) {
             inputField.clear();
+            String currentUsername = controller.getCurrentUsername();
             Message msg =
                     new Message(
                             chatModel.getChattype(),
                             chatModel.lobbyId,
-                            username,
+                            currentUsername,
                             chatModel.getTarget(),
                             message);
             controller.onSendToNetwork(msg);

src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/ui/gameui/CasinoGameUI.java

@@ -114,8 +114,11 @@ public class CasinoGameUI extends Application {
         Parent root = fxmlLoader.load();
         CasinoGameController controller = fxmlLoader.getController();
 
-        int gameId = 1; // TODO echte gameId einsetzen
-        GameClient gameClient = new GameClient(clientService, gameId);
+        if (lobbyId <= 0) {
+            throw new IllegalStateException("CasinoGameUI: lobbyId must be set before start()");
+        }
+
+        GameClient gameClient = new GameClient(clientService, lobbyId);
         GameService gameService = new GameService(gameClient);
         controller.setGameService(gameService);
 

src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/ui/lobbyui/CasinomainuiController.java

@@ -104,6 +104,13 @@ public class CasinomainuiController {
         casinoTable.getChildren().add(gridManager.getGridPane());
         gridManager.renderLobbyButtons();
 
+        String sharedUsername = ClientApp.getSharedUsername();
+        updateUsernameFieldPresentation(sharedUsername);
+        if (loginButton != null) {
+            loginButton.setText(
+                    sharedUsername != null && !sharedUsername.isBlank() ? "Change Name" : "Login");
+        }
+
         initializeChat(clientService);
     }
 
@@ -156,7 +163,7 @@ public class CasinomainuiController {
     /** Handles the login button action. Validates input and calls LobbyClient.login(). */
     @FXML
     public void handleLoginButton() {
-        String username = usernameField.getText();
+        String username = usernameField == null ? null : usernameField.getText();
         if (username == null || username.isBlank()) {
             showAlert("Please enter a username.");
             return;
@@ -170,12 +177,63 @@ public class CasinomainuiController {
             showAlert("Offline mode: cannot send login to server.");
             return;
         }
+
+        String trimmed = username.trim();
         try {
-            lobbyClient.login(username);
-            showAlert("Login sent: " + username);
+            var result = lobbyClient.login(trimmed);
+            String assigned = result != null ? result.getUsername() : trimmed;
+            ClientApp.updateSharedUsername(assigned);
+            if (chatController != null) {
+                chatController.updateUsername(assigned);
+            }
+            updateUsernameFieldPresentation(assigned);
+            if (loginButton != null) {
+                loginButton.setText("Change Name");
+            }
+            return;
+        } catch (RuntimeException loginError) {
+            if (!containsProtocolError(loginError, "ALREADY_LOGGED_IN")) {
+                LOGGER.error("Login failed: {}", loginError.getMessage());
+                showAlert("Login failed: " + loginError.getMessage());
+                return;
+            }
+            LOGGER.info("Session already logged in, trying username change");
+        }
+
+        try {
+            var result = lobbyClient.changeUsername(trimmed);
+            String assigned = result != null ? result.getUsername() : trimmed;
+            ClientApp.updateSharedUsername(assigned);
+            if (chatController != null) {
+                chatController.updateUsername(assigned);
+            }
+            updateUsernameFieldPresentation(assigned);
+            if (loginButton != null) {
+                loginButton.setText("Change Name");
+            }
         } catch (RuntimeException e) {
-            LOGGER.error("Login failed: {}", e.getMessage());
-            showAlert("Login failed: " + e.getMessage());
+            LOGGER.error("Change username failed: {}", e.getMessage());
+            showAlert("Change username failed: " + e.getMessage());
+        }
+    }
+
+    private boolean containsProtocolError(RuntimeException error, String code) {
+        String msg = error.getMessage();
+        return msg != null && msg.contains(code);
+    }
+
+    private void updateUsernameFieldPresentation(String username) {
+        if (usernameField == null) {
+            return;
+        }
+
+        if (username != null && !username.isBlank()) {
+            usernameField.setText(username.trim());
+            usernameField.positionCaret(usernameField.getText().length());
+            usernameField.setPromptText("Username");
+        } else {
+            usernameField.clear();
+            usernameField.setPromptText("Username");
         }
     }
 

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/game/get_game_state/GetGameStateHandler.java

@@ -1,6 +1,7 @@
 package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.game.get_game_state;
 
 import ch.unibas.dmi.dbis.cs108.casono.server.app.checks.UserLoggedInCheck;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.state.GamePhase;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby.Lobby;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby.LobbyId;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby.LobbyManager;
@@ -31,8 +32,10 @@ public class GetGameStateHandler extends CommandHandler<GetGameStateRequest> {
         String username = resolveUsername(request);
 
         Lobby lobby;
+        LobbyId lobbyId;
         if (gameId != null) {
-            lobby = lobbyManager.getLobby(LobbyId.of(gameId));
+            lobbyId = LobbyId.of(gameId);
+            lobby = lobbyManager.getLobby(lobbyId);
             if (lobby == null) {
                 responseDispatcher.dispatch(
                         new ErrorResponse(
@@ -59,6 +62,7 @@ public class GetGameStateHandler extends CommandHandler<GetGameStateRequest> {
                                 request.getContext(), "NOT_IN_LOBBY", "User not in a lobby"));
                 return;
             }
+            lobbyId = lobby.getId();
         }
 
         var game = lobby.getGameController();
@@ -69,9 +73,30 @@ public class GetGameStateHandler extends CommandHandler<GetGameStateRequest> {
             return;
         }
 
+        if (game.getState().getPhase() == GamePhase.FINISHED) {
+            cleanupLobby(lobby, lobbyId);
+        }
+
         responseDispatcher.dispatch(new GetGameStateResponse(request.getContext(), game, username));
     }
 
+    /**
+     * Cleans up a lobby by removing all players and resetting the game controller. This is called
+     * when the game reaches FINISHED phase.
+     */
+    private void cleanupLobby(Lobby lobby, LobbyId lobbyId) {
+        try {
+            // Remove all players from the lobby
+            for (String playerName : lobby.getPlayerNames()) {
+                lobbyManager.removePlayer(playerName);
+            }
+            // Reset the game controller so the lobby returns to CREATED state
+            lobby.initGame(null);
+        } catch (RuntimeException e) {
+            // Log silently to avoid disrupting game state response
+        }
+    }
+
     private String resolveUsername(GetGameStateRequest request) {
         String username = request.getUsername();
         if (username != null && !username.isBlank()) {

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/game/get_game_state/GetGameStateResponse.java

@@ -6,6 +6,7 @@ import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.deck.Rank;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.deck.Suit;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.player.Player;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.player.PlayerId;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.state.GamePhase;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.state.GameState;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.SuccessResponse;
@@ -33,11 +34,13 @@ public class GetGameStateResponse extends SuccessResponse {
         super(
                 context,
                 buildBody(
+                        game,
                         Objects.requireNonNull(game, "game must not be null").getState(),
                         requestingUsername));
     }
 
-    private static ResponseBody buildBody(GameState state, String requestingUsername) {
+    private static ResponseBody buildBody(
+            GameController game, GameState state, String requestingUsername) {
         Objects.requireNonNull(state, "state must not be null");
 
         ResponseBodyBuilder builder = ResponseBody.builder();
@@ -47,6 +50,7 @@ public class GetGameStateResponse extends SuccessResponse {
         builder.param("CURRENT_BET", computeGlobalCurrentBet(state));
         builder.param("DEALER", state.getDealerIndex());
         builder.param("ACTIVE_PLAYER", state.getCurrentPlayerIndex());
+        builder.param("WINNER", computeWinnerIndex(state, game));
 
         appendCommunityCards(builder, state);
 
@@ -55,6 +59,28 @@ public class GetGameStateResponse extends SuccessResponse {
         return builder.build();
     }
 
+    private static int computeWinnerIndex(GameState state, GameController game) {
+        GamePhase phase = state.getPhase();
+        if (phase != GamePhase.SHOWDOWN && phase != GamePhase.FINISHED) {
+            return -1;
+        }
+
+        PlayerId winnerId = game.determineWinner();
+        if (winnerId == null) {
+            return -1;
+        }
+
+        int index = 0;
+        for (Player p : state.getPlayers()) {
+            if (p != null && winnerId.equals(p.getId())) {
+                return index;
+            }
+            index++;
+        }
+
+        return -1;
+    }
+
     private static int computeGlobalCurrentBet(GameState state) {
         int globalCurrentBet = 0;
         for (Player p : state.getPlayers()) {

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/send_message/SendMessageHandler.java

@@ -9,6 +9,7 @@ import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.UserRegistry;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.command.execution.CommandHandler;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.OkResponse;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher.ResponseDispatcher;
+import java.util.Optional;
 
 public class SendMessageHandler extends CommandHandler<SendMessageRequest> {
     private final UserRegistry userRegistry;
@@ -39,6 +40,11 @@ public class SendMessageHandler extends CommandHandler<SendMessageRequest> {
     @Override
     public void execute(SendMessageRequest request) {
         Message message = request.getMessage();
+        Optional<ch.unibas.dmi.dbis.cs108.casono.server.domain.user.User> senderUser =
+                userRegistry.getBySessionId(request.getSessionId());
+        if (senderUser.isPresent()) {
+            message.sender = senderUser.get().getName();
+        }
         broadcast(request, message);
         OkResponse response = new OkResponse(request.getContext());
         responseDispatcher.dispatch(response);

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/domain/game/GameController.java

@@ -61,6 +61,35 @@ public class GameController {
         engine.getState().addPlayer(name, chips);
     }
 
+    /**
+     * Renames a player id in the controller list and underlying game state.
+     *
+     * @param oldId old player id
+     * @param newId new player id
+     * @return true if rename succeeded
+     */
+    public boolean renamePlayer(PlayerId oldId, PlayerId newId) {
+        if (oldId == null || newId == null) {
+            return false;
+        }
+        if (oldId.equals(newId)) {
+            return true;
+        }
+
+        int idx = players.indexOf(oldId);
+        if (idx < 0 || players.contains(newId)) {
+            return false;
+        }
+
+        boolean stateRenamed = engine.getState().renamePlayerId(oldId, newId);
+        if (!stateRenamed) {
+            return false;
+        }
+
+        players.set(idx, newId);
+        return true;
+    }
+
     /**
      * Initializes a new hand by preparing the deck, setting the phase to PREFLOP, rotating the
      * dealer, dealing hole cards, posting blinds, and setting the first active player.
@@ -254,4 +283,12 @@ public class GameController {
 
         return bestPlayer;
     }
+
+    /**
+     * Ends the current game by setting the phase to FINISHED. This should be called when the
+     * showdown is complete and a winner has been determined.
+     */
+    public void endGame() {
+        engine.getState().setPhase(GamePhase.FINISHED);
+    }
 }

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/domain/game/engine/RoundManager.java

@@ -49,6 +49,11 @@ public class RoundManager {
             state.setPhase(GamePhase.PREFLOP);
         }
 
+        if (state.countNonFoldedPlayers() == 1) {
+            state.setPhase(GamePhase.FINISHED);
+            return;
+        }
+
         if (isBettingRoundFinished(state)) {
             advancePhase(state);
         }
@@ -81,8 +86,9 @@ public class RoundManager {
             case FLOP -> dealTurn(state);
             case TURN -> dealRiver(state);
             case RIVER -> showdown(state);
-            case SHOWDOWN -> {
-                /* nothing */
+            case SHOWDOWN -> state.setPhase(GamePhase.FINISHED);
+            case FINISHED -> {
+                /* game is over */
             }
         }
     }

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/domain/game/player/Player.java

@@ -49,6 +49,16 @@ public class Player {
         return id;
     }
 
+    /**
+     * Updates the player's id. This is used when a username change is propagated into an already
+     * running game.
+     *
+     * @param id new player id
+     */
+    public void setId(PlayerId id) {
+        this.id = id;
+    }
+
     /**
      * Returns the display name of the player. Currently identical to the player ID.
      *

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/domain/game/state/GameState.java

@@ -11,18 +11,14 @@ import java.util.List;
 import java.util.Map;
 
 /**
- * The GameState class encapsulates the entire state of a poker game at any
- * given moment.
+ * The GameState class encapsulates the entire state of a poker game at any given moment.
  *
- * <p>
- * Important invariants this implementation maintains:
+ * <p>Important invariants this implementation maintains:
  *
  * <ul>
  *   <li>{@code playerOrder} defines the stable seating/turn order.
- * <li>{@code currentBets} always contains an entry for every player in
- * {@code playerOrder}.
- * <li>{@code holeCards} maps every player to a mutable list; if not present, it
- * is created on
+ *   <li>{@code currentBets} always contains an entry for every player in {@code playerOrder}.
+ *   <li>{@code holeCards} maps every player to a mutable list; if not present, it is created on
  *       demand.
  * </ul>
  */
@@ -178,6 +174,51 @@ public class GameState {
         holeCards.computeIfAbsent(id, k -> new ArrayList<>());
     }
 
+    /**
+     * Renames a player id across all game-state structures.
+     *
+     * @param oldId existing player id
+     * @param newId new player id
+     * @return true if the rename was applied, false otherwise
+     */
+    public synchronized boolean renamePlayerId(PlayerId oldId, PlayerId newId) {
+        if (oldId == null || newId == null) {
+            return false;
+        }
+        if (!players.containsKey(oldId)) {
+            return false;
+        }
+        if (oldId.equals(newId)) {
+            return true;
+        }
+        if (players.containsKey(newId)) {
+            return false;
+        }
+
+        Player player = players.remove(oldId);
+        if (player == null) {
+            return false;
+        }
+        player.setId(newId);
+        players.put(newId, player);
+
+        int idx = playerOrder.indexOf(oldId);
+        if (idx >= 0) {
+            playerOrder.set(idx, newId);
+        }
+
+        moveMapEntry(currentBets, oldId, newId, 0);
+        moveMapEntry(playerBetCommitments, oldId, newId, 0);
+        moveMapEntry(holeCards, oldId, newId, new ArrayList<>());
+        return true;
+    }
+
+    private <T> void moveMapEntry(
+            Map<PlayerId, T> map, PlayerId oldId, PlayerId newId, T fallback) {
+        T value = map.remove(oldId);
+        map.put(newId, value != null ? value : fallback);
+    }
+
     // Betting
     public int getCurrentBet(PlayerId playerId) {
         return currentBets.getOrDefault(playerId, 0);
@@ -188,8 +229,7 @@ public class GameState {
     }
 
     /**
-     * Reset bets to 0 for ALL players (do not clear the map). Also resets table
-     * current bet to 0.
+     * Reset bets to 0 for ALL players (do not clear the map). Also resets table current bet to 0.
      */
     public void resetBets() {
         for (PlayerId id : playerOrder) {
@@ -232,8 +272,7 @@ public class GameState {
     // Cards
 
     /**
-     * Gives (overwrites) the two hole cards for the given player. Ensures stable
-     * list identity
+     * Gives (overwrites) the two hole cards for the given player. Ensures stable list identity
      * (important if other code holds references).
      */
     public void giveHoleCards(PlayerId playerId, Card c1, Card c2) {
@@ -293,8 +332,7 @@ public class GameState {
     /**
      * Starts a new hand by resetting the game state for the next round of poker.
      *
-     * <p>
-     * This:
+     * <p>This:
      *
      * <ul>
      *   <li>sets {@code phase=PREFLOP}
@@ -336,4 +374,19 @@ public class GameState {
     public boolean isFolded(PlayerId playerId) {
         return getPlayer(playerId).isFolded();
     }
+
+    /**
+     * Counts the number of players who have not folded.
+     *
+     * @return The number of non-folded players
+     */
+    public int countNonFoldedPlayers() {
+        int count = 0;
+        for (Player p : players.values()) {
+            if (p != null && !p.isFolded()) {
+                count++;
+            }
+        }
+        return count;
+    }
 }

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/domain/lobby/Lobby.java

@@ -70,6 +70,30 @@ public class Lobby {
         return playerNames.remove(playerName);
     }
 
+    /**
+     * Renames a player in this lobby's player list.
+     *
+     * @param oldName old username
+     * @param newName new username
+     * @return true if renamed successfully
+     */
+    public boolean renamePlayer(String oldName, String newName) {
+        if (oldName == null || newName == null) {
+            return false;
+        }
+        synchronized (playerNames) {
+            if (oldName.equals(newName)) {
+                return playerNames.contains(oldName);
+            }
+            int idx = playerNames.indexOf(oldName);
+            if (idx < 0 || playerNames.contains(newName)) {
+                return false;
+            }
+            playerNames.set(idx, newName);
+            return true;
+        }
+    }
+
     public void initGame(GameController controller) {
         this.gameController = controller;
     }

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/domain/lobby/LobbyManager.java

@@ -1,5 +1,6 @@
 package ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby;
 
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.player.PlayerId;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby.Lobby.AddResult;
 import java.time.Duration;
 import java.time.Instant;
@@ -170,6 +171,56 @@ public class LobbyManager {
         }
     }
 
+    /**
+     * Renames a player across lobby mapping, lobby player list and running game ids.
+     *
+     * @param oldUsername old username
+     * @param newUsername new username
+     * @return true if rename was applied
+     */
+    public synchronized boolean renamePlayer(String oldUsername, String newUsername) {
+        if (oldUsername == null || newUsername == null) {
+            return false;
+        }
+        if (oldUsername.equals(newUsername)) {
+            return true;
+        }
+
+        LobbyId lobbyId = playerToLobby.get(oldUsername);
+        if (lobbyId == null) {
+            return true;
+        }
+        if (playerToLobby.containsKey(newUsername)) {
+            return false;
+        }
+
+        Lobby lobby = activeLobbies.get(lobbyId);
+        if (lobby == null) {
+            playerToLobby.remove(oldUsername);
+            return true;
+        }
+
+        boolean lobbyRenamed = lobby.renamePlayer(oldUsername, newUsername);
+        if (!lobbyRenamed) {
+            return false;
+        }
+
+        if (lobby.getGameController() != null) {
+            boolean gameRenamed =
+                    lobby.getGameController()
+                            .renamePlayer(PlayerId.of(oldUsername), PlayerId.of(newUsername));
+            if (!gameRenamed) {
+                // Best-effort rollback to keep structures consistent.
+                lobby.renamePlayer(newUsername, oldUsername);
+                return false;
+            }
+        }
+
+        playerToLobby.remove(oldUsername);
+        playerToLobby.put(newUsername, lobbyId);
+        return true;
+    }
+
     /**
      * Apply the given action to every player username in the lobby identified by {@code lobbyId}.
      * This is a small helper that keeps iteration logic centralized and avoids leaking internal

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/domain/user/UserRegistry.java

@@ -200,6 +200,10 @@ public class UserRegistry {
             return false;
         }
 
+        if (user.getName().equals(newName)) {
+            return true;
+        }
+
         if (byName.containsKey(newName)) {
             return false;
         }

src/main/resources/ui-structure/Casinomainui.fxml

@@ -81,25 +81,24 @@
                         </GridPane.margin>
                     </Button>
 
-                        <!-- Username input and login button -->
-                            <!-- <HBox alignment="CENTER_LEFT" spacing="10"-->
-                            <!--             GridPane.rowIndex="0"-->
-                            <!--             GridPane.columnIndex="0"-->
-                            <!--             GridPane.halignment="LEFT"-->
-                            <!--             GridPane.valignment="TOP">-->
-                            <!--         <GridPane.margin>-->
-                            <!--                 &lt;!&ndash; place below the 'CREATE A LOBBY' button &ndash;&gt;-->
-                            <!--                 <Insets top="100" left="20" />-->
-                            <!--         </GridPane.margin>-->
-                            <!--         <TextField fx:id="usernameField"-->
-                            <!--                    promptText="Username"-->
-                            <!--                    styleClass="gray-input-field"-->
-                            <!--                    maxWidth="180" />-->
-                            <!--         <Button text="Login"-->
-                            <!--                         fx:id="loginButton"-->
-                            <!--                         onAction="#handleLoginButton"-->
-                            <!--                         styleClass="button-create-lobby" />-->
-                            <!-- </HBox>-->
+                        <!-- Username input and login/change button -->
+                        <HBox alignment="CENTER_LEFT" spacing="10"
+                              GridPane.rowIndex="0"
+                              GridPane.columnIndex="0"
+                              GridPane.halignment="LEFT"
+                              GridPane.valignment="TOP">
+                            <GridPane.margin>
+                                <Insets top="100" left="20" />
+                            </GridPane.margin>
+                            <TextField fx:id="usernameField"
+                                       promptText="Username"
+                                       styleClass="gray-input-field"
+                                       maxWidth="180" />
+                            <Button text="Apply Name"
+                                    fx:id="loginButton"
+                                    onAction="#handleLoginButton"
+                                    styleClass="button-create-lobby" />
+                        </HBox>
 
                     <VBox fx:id="casinoTable"
                           alignment="CENTER"