Feat: Added CHANGE_USERNAME server command, registration and documentation

Feat: Auto-cleanup lobbies when game finishes

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

documents/docs/networking/commands/protocol-document.md

@@ -1,8 +1,9 @@
 # Protocol Document
+
 This document describes the protocol for client-server communication in our application. It defines the structure of requests and responses, the supported commands along with their request parameters, response formats, and possible errors.
 
-
 # Table of Contents
+
 - [Protocol Document](#protocol-document)
 - [Table of Contents](#table-of-contents)
 - [General structure of requests](#general-structure-of-requests)
@@ -36,20 +37,27 @@ This document describes the protocol for client-server communication in our appl
     - [Error Response](#error-response-4)
     - [Example Request](#example-request-2)
     - [Example Response](#example-response-2)
-  - [LOGOUT command](#logout-command)
+  - [CHANGE\_USERNAME command](#change_username-command)
     - [Required pre-execution checks](#required-pre-execution-checks-3)
     - [Request Parameters](#request-parameters-3)
     - [Success Response](#success-response-3)
     - [Error Response](#error-response-5)
     - [Example Request](#example-request-3)
     - [Example Response](#example-response-3)
-  - [LIST\_USERS command](#list_users-command)
+  - [LOGOUT command](#logout-command)
     - [Required pre-execution checks](#required-pre-execution-checks-4)
     - [Request Parameters](#request-parameters-4)
     - [Success Response](#success-response-4)
     - [Error Response](#error-response-6)
     - [Example Request](#example-request-4)
     - [Example Response](#example-response-4)
+  - [LIST\_USERS command](#list_users-command)
+    - [Required pre-execution checks](#required-pre-execution-checks-5)
+    - [Request Parameters](#request-parameters-5)
+    - [Success Response](#success-response-5)
+    - [Error Response](#error-response-7)
+    - [Example Request](#example-request-5)
+    - [Example Response](#example-response-5)
   - [GET_LOBBY_LIST command](#get_lobby_list-command)
     - [Required pre-execution checks](#required-pre-execution-checks)
     - [Request Parameters](#request-parameters)
@@ -91,6 +99,7 @@ This document describes the protocol for client-server communication in our appl
 <!-- Please see the comments for copy ‚ n' paste ready examples -->
 
 # General structure of requests
+
 As mentioned before, our protocol is based on POP3.
 Each command is represented as a single line of text, starting with the command name followed by parameters. The server responds with a status line indicating success or failure, followed by the body.
 
@@ -99,41 +108,43 @@ Requests can have parameters that provide additional information for the command
 Responses are collections of key-value pairs, containing either a value or another collection, allowing for nested structures.
 Each collection is ended with the `END` keyword.
 
-
-
 # Preconditions
+
 The serverside pipeline to process incoming requests consists of multiple stages.
 Each of these stages can yield an error response if the request does not meet the requirements of that stage.
 
 ## Parsing
+
 One of these stages is the parsing. It is responsible for parsing the raw request into a structured format that can be easily processed by the command handlers. It validates the syntax of the request as well.
 
 ### Error Response
+
 | Code            | Description                                                                                     |
 | :-------------- | :---------------------------------------------------------------------------------------------- |
 | `PARSING_ERROR` | The body of the request contains syntax errors (see message field of response for more details) |
 
-
 ## Command dispatching
+
 After the request has been successfully parsed, the next stage is to dispatch the `PrimitiveRequest` to the appropriate `CommandParser`. This is done by the `CommandDispatcherDispatcher`, which uses the command name to determine which parser to use.
 
 ### Error Response
+
 | Code              | Description                                                       |
 | :---------------- | :---------------------------------------------------------------- |
 | `UNKNOWN_COMMAND` | The command is unknown to this server. No parser has been defined |
 
-
 ## Command parsing
+
 Once the `PrimitiveRequest` has been dispatched to the appropriate `CommandParser`, the parser is responsible for parsing the parameters of the request and creating a `Request` that can be executed by the responsible `CommandHandler`.
 
 ### Error Response
+
 | Code                | Description                                                                                       |
 | :------------------ | :------------------------------------------------------------------------------------------------ |
 | `MISSING_PARAMETER` | A required parameter is missing from the request (see message field of response for more details) |
 
-
-
 # Pre-execution checks
+
 Pre-execution checks are reusable validation steps that can be registered on command handlers.
 They are implemented as `HandlerCheck` instances and are executed by the `CommandHandlerExecutor` before the handler's main logic is invoked.
 
@@ -148,16 +159,17 @@ Description of the check, what it does and when it should be used.
 -->
 
 ## UserLoggedInCheck
+
 The `UserLoggedInCheck` is a common pre-execution check that verifies whether the user is logged in (i.e. has a user associated with his session).
 
 ### Error Response
+
 | Code                 | Description               |
 | :------------------- | :------------------------ |
 | `USER_NOT_LOGGED_IN` | The user is not logged in |
 
-
-
 # Commands
+
 Commands are the core of our protocol, representing the various actions that clients can request from the server. Each command has a unique name and may require specific parameters in addition to pre-execution checks.
 The server processes these commands and responds accordingly.
 
@@ -212,41 +224,50 @@ END
 -->
 
 ## PING command
+
 The `PING` command is a simple command that can be used to check if the server is responsive.
 
 ### Required pre-execution checks
+
 None.
 
 ### Request Parameters
+
 No parameters.
 
 ### Success Response
+
 No response fields.
 
 ### Example Request
+
 ```
 PING
 ```
 
 ### Example Response
+
 ```
 +OK
 END
 ```
 
-
 ## CHECK_USERNAME command
+
 The `CHECK_USERNAME` command is used to check if a username is already taken by another user. Additional users can still log in with the same username, but their name will be substituted with a suffix.
 
 ### Required pre-execution checks
+
 None.
 
 ### Request Parameters
+
 | Parameter Name | Type     | Optional | Description                            |
 | :------------- | :------- | :------- | :------------------------------------- |
 | `USERNAME`     | `String` | no       | The username to check for availability |
 
 ### Success Response
+
 | Field    | Type                         | Description                                                             |
 | :------- | :--------------------------- | :---------------------------------------------------------------------- |
 | `STATUS` | `Enum<UsernameAvailability>` | Member of enum indicating if the username is available or already taken |
@@ -257,11 +278,13 @@ None.
 | `TAKEN`                           | Username is already in use |
 
 ### Example Request
+
 ```
 CHECK_USERNAME USERNAME='Lars'
 ```
 
 ### Example Response
+
 ```
 +OK 
   STATUS=FREE
@@ -269,33 +292,40 @@ END
 ```
 
 ## LOGIN command
+
 The `LOGIN` command is used to log in a user with a specified username. If the username is already taken by another user, the server will append a suffix to the username to make it unique.
 
 ### Required pre-execution checks
+
 None.
 
 ### Request Parameters
+
 | Parameter Name | Type     | Optional | Description                          |
 | :------------- | :------- | :------- | :----------------------------------- |
 | `USERNAME`     | `String` | no       | The username to create the user with |
 
 ### Success Response
+
 | Field      | Type                                                                    | Description                                                           |
 | :--------- | :---------------------------------------------------------------------- | :-------------------------------------------------------------------- |
 | `USERNAME` | `String`                                                                | Username of the newly created user, can differ from the requested one |
 | `ID`       | [`UUID`](https://docs.oracle.com/javase/8/docs/api/java/util/UUID.html) | The ID of the created user                                            |
 
 ### Error Response
+
 | Code                | Description                                                                    |
 | :------------------ | :----------------------------------------------------------------------------- |
 | `ALREADY_LOGGED_IN` | The session is already associated with a user, logging in again is prohibited. |
 
 ### Example Request
+
 ```
 LOGIN USERNAME='Lars'
 ```
 
 ### Example Response
+
 ```
 +OK
   USERNAME='Lars_1234'
@@ -303,45 +333,100 @@ LOGIN USERNAME='Lars'
 END
 ```
 
+## CHANGE_USERNAME command
 
-## LOGOUT command
+The `CHANGE_USERNAME` command is used to change the username of an already logged-in user. The request is tied to the current session and updates all affected server-side mappings.
-Description of the command, what it does, and when it should be used.
 
 ### Required pre-execution checks
+
 None.
 
 ### Request Parameters
+
+| Parameter Name | Type     | Optional | Description                           |
+| :------------- | :------- | :------- | :------------------------------------ |
+| `USERNAME`     | `String` | no       | The new username for the active user  |
+
+### Success Response
+
+| Field      | Type                                                                    | Description                             |
+| :--------- | :---------------------------------------------------------------------- | :-------------------------------------- |
+| `USERNAME` | `String`                                                                | Effective username after rename         |
+| `ID`       | [`UUID`](https://docs.oracle.com/javase/8/docs/api/java/util/UUID.html) | The ID of the renamed user              |
+
+### Error Response
+
+| Code                 | Description                                                           |
+| :------------------- | :-------------------------------------------------------------------- |
+| `USER_NOT_LOGGED_IN` | No active user is associated with this session.                       |
+| `INVALID_USERNAME`   | Username contains disallowed characters or is empty.                  |
+| `USERNAME_TAKEN`     | Requested username is already used by another user.                   |
+| `RENAME_CONFLICT`    | Rename could not be propagated to all current lobby/game structures.  |
+
+### Example Request
+
+```
+CHANGE_USERNAME USERNAME='Lars_New'
+```
+
+### Example Response
+
+```
++OK
+  USERNAME='Lars_New'
+  ID=e47a671e-2b2a-42df-bb82-953fe2ebd307
+END
+```
+
+## LOGOUT command
+
+Description of the command, what it does, and when it should be used.
+
+### Required pre-execution checks
+
+None.
+
+### Request Parameters
+
 No parameters.
 
 ### Success Response
+
 No response fields.
 
 ### Error Response
+
 | Code                 | Description                                                      |
 | :------------------- | :--------------------------------------------------------------- |
 | `NO_USER_ASSOCIATED` | The session has no user associated, logging out is not possible. |
 
 ### Example Request
+
 ```
 LOGOUT
 ```
 
 ### Example Response
+
 ```
 +OK
 END
 ```
 
 ## LIST_USERS command
+
 The `LIST_USERS` command is used to retrieve a list of all currently logged-in users.
 
 ### Required pre-execution checks
+
 None.
 
 ### Request Parameters
+
 No parameters.
 
 ### Success Response
+
 | Field   | Type               | Description                              |
 | :------ | :----------------- | :--------------------------------------- |
 | `USERS` | `Collection<User>` | Collection of all users currently online |
@@ -351,16 +436,18 @@ No parameters.
 | `USERNAME`       | `String`                                                                | Username of the newly created user, can differ from the requested one |
 | `ID`             | [`UUID`](https://docs.oracle.com/javase/8/docs/api/java/util/UUID.html) | The ID of the created user                                            |
 
-
 ### Error Response
+
 None.
 
 ### Example Request
+
 ```
 LIST_USERS
 ```
 
 ### Example Response
+
 ```
 +OK
   USERS
@@ -381,8 +468,11 @@ END
 ```
 
 ## SEND_MESSAGE command
+
 The `SEND_MESSAGE` command is used to transfer the chat message sent by a user to the server.
+
 ### Required pre-execution checks
+
 None.
 
 ### Request Parameters
@@ -403,28 +493,36 @@ None.
 | `WHISPER`             | Message is for the whisper chat |
 
 ### Success Response
+
 No response fields.
 
 ### Error Response
+
 None.
 
 ### Example Request
+
 ```
 SEND_MESSAGE TYPE=GLOBAL GAME=1 USER=player1 TARGET=null TIME='10:30' TEXT='Hello World'
 ```
 
 ### Example Response
+
 ```
 +OK
 END
 ```
 
 ## GET_MESSAGE_COUNT command
+
 The `GET_MESSAGE_COUNT` is used to get the current number of messages that are stored in the queue for a client.
+
 ### Required pre-execution checks
+
 None.
 
 ### Request Parameters
+
 No parameters.
 
 ### Success Response
@@ -434,17 +532,19 @@ No parameters.
 | `COUNT` | `int` | The current number of messages |
 
 ### Error Response
+
 | Code                 | Description                                                                      |
 | :------------------- |:---------------------------------------------------------------------------------|
 | `NO_USER_ASSOCIATED` | The session has no user associated, there is no queue of messages for the client |
 
-
 ### Example Request
+
 ```
 GET_MESSAGE_COUNT
 ```
 
 ### Example Response
+
 ```
 +OK
 COUNT=10
@@ -452,14 +552,19 @@ END
 ```
 
 ## GET_NEXT_MESSAGE command
+
 The `GET_NEXT_MESSAGE` command is used to get the next message stored in a queue for the client.
+
 ### Required pre-execution checks
+
 None.
 
 ### Request Parameters
+
 No parameters.
 
 ### Success Response
+
 | Field    | Type            | Description                                                        |
 |:---------|:----------------|:-------------------------------------------------------------------|
 | `TYPE`   | `Enum<ChatType` | Member of Enum, indicating with chat type is used                  |
@@ -476,16 +581,19 @@ No parameters.
 | `WHISPER`             | Message is for the whisper chat |
 
 ### Error Response
+
 | Code                 | Description                                                                      |
 | :------------------- |:---------------------------------------------------------------------------------|
 | `NO_USER_ASSOCIATED` | The session has no user associated, there is no queue of messages for the client |
 
 ### Example Request
+
 ```
 GET_NEXT_MESSAGE
 ```
 
 ### Example Response
+
 ```
 +OK
 TYPE=GLOBAL GAME=-1 USER=player1 TARGET=null TIME=9:30 TEXT="Guten Tag"
@@ -613,9 +721,11 @@ END
 The `GET_LOBBY_LIST` command requests the server to return a list of currently available lobbies with basic metadata.
 
 ### Required pre-execution checks
+
 None.
 
 ### Request Parameters
+
 No parameters.
 
 ### Implementation notes
@@ -667,9 +777,11 @@ END
 The `GET_GAME_STATE` command returns a snapshot of the current game for a lobby. It includes global fields (`PHASE`, `POT`, `CURRENT_BET`, `DEALER`, `ACTIVE_PLAYER`), repeated `CARD` blocks for community cards and repeated `PLAYER` blocks for per-player information. If the requester is a player in the game, their hole cards are included inside their `PLAYER` block as nested `CARD` blocks.
 
 ### Required pre-execution checks
+
 - [`UserLoggedInCheck`](#userloggedincheck)
 
 ### Request Parameters
+
 | Parameter Name | Type   | Optional | Description |
 | :------------- | :----- | :------: | :---------- |
 | `GAME_ID`      | `int`  | yes      | Numeric id of the lobby/game to query. If omitted the server will resolve the lobby by the requesting session's associated user.
@@ -1114,9 +1226,11 @@ END
 The `GET_LOBBY_STATUS` command requests the server to return the current state of a lobby, including the list of players and their ready state.
 
 ### Required pre-execution checks
+
 None.
 
 ### Request Parameters
+
 | Parameter Name | Type | Optional | Description |
 | :------------- | :--- | :------: | :---------- |
 | `ID` | `int` | no | Numeric id of the target lobby |
@@ -1151,6 +1265,7 @@ END
 ```
 
 ### Error Response
+
 | Code | Description |
 | :--- | :---------- |
 | `LOBBY_NOT_FOUND` | The specified lobby id does not exist |

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
+        if (lobbyId <= 0) {
-        GameClient gameClient = new GameClient(clientService, gameId);
+            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/server/ServerApp.java

@@ -1,5 +1,8 @@
 package ch.unibas.dmi.dbis.cs108.casono.server;
 
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.change_username.ChangeUsernameHandler;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.change_username.ChangeUsernameParser;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.change_username.ChangeUsernameRequest;
 import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick.CheckUsernameHandler;
 import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick.CheckUsernameParser;
 import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick.CheckUsernameRequest;
@@ -168,6 +171,15 @@ public class ServerApp {
         commandRouter.register(
                 LoginRequest.class, new LoginHandler(responseDispatcher, userRegistry));
 
+        parserDispatcher.register("CHANGE_USERNAME", new ChangeUsernameParser());
+        commandRouter.register(
+                ChangeUsernameRequest.class,
+                new ChangeUsernameHandler(
+                        responseDispatcher,
+                        userRegistry,
+                        context.lobbyManager(),
+                        context.sessionManager()));
+
         parserDispatcher.register("LOGOUT", new LogoutParser());
         commandRouter.register(
                 LogoutRequest.class, new LogoutHandler(responseDispatcher, userRegistry));

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/change_username/ChangeUsernameHandler.java

@@ -0,0 +1,112 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.change_username;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby.LobbyManager;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.User;
+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.request.RequestContext;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.ErrorResponse;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.SuccessResponse;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.builder.ResponseBodyBuilder;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher.ResponseDispatcher;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.Session;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionManager;
+import java.util.Optional;
+import java.util.regex.Pattern;
+
+/** Handles CHANGE_USERNAME requests for already logged-in users. */
+public class ChangeUsernameHandler extends CommandHandler<ChangeUsernameRequest> {
+    private static final Pattern VALID_USERNAME = Pattern.compile("[a-zA-Z0-9_-]+");
+    private final UserRegistry userRegistry;
+    private final LobbyManager lobbyManager;
+    private final SessionManager sessionManager;
+
+    /**
+     * @param responseDispatcher dispatcher used for responses
+     * @param userRegistry registry containing all users
+     * @param lobbyManager lobby manager used to keep lobby/game mappings in sync
+     * @param sessionManager session manager used to broadcast rename events
+     */
+    public ChangeUsernameHandler(
+            ResponseDispatcher responseDispatcher,
+            UserRegistry userRegistry,
+            LobbyManager lobbyManager,
+            SessionManager sessionManager) {
+        super(responseDispatcher);
+        this.userRegistry = userRegistry;
+        this.lobbyManager = lobbyManager;
+        this.sessionManager = sessionManager;
+    }
+
+    @Override
+    public void execute(ChangeUsernameRequest request) {
+        Optional<User> user = userRegistry.getBySessionId(request.getSessionId());
+        if (user.isEmpty()) {
+            responseDispatcher.dispatch(
+                    new ErrorResponse(
+                            request.getContext(),
+                            "USER_NOT_LOGGED_IN",
+                            "This session is not associated with an active user."));
+            return;
+        }
+
+        String newUsername = request.getUsername() == null ? "" : request.getUsername().trim();
+        if (newUsername.isEmpty() || !VALID_USERNAME.matcher(newUsername).matches()) {
+            responseDispatcher.dispatch(
+                    new ErrorResponse(
+                            request.getContext(),
+                            "INVALID_USERNAME",
+                            "Only letters, numbers, '_' and '-' are allowed."));
+            return;
+        }
+
+        User currentUser = user.get();
+        String oldUsername = currentUser.getName();
+        boolean changed = userRegistry.changeUsername(currentUser.getId(), newUsername);
+        if (!changed) {
+            responseDispatcher.dispatch(
+                    new ErrorResponse(
+                            request.getContext(),
+                            "USERNAME_TAKEN",
+                            "The requested username is already taken."));
+            return;
+        }
+
+        boolean lobbySynced =
+                lobbyManager == null || lobbyManager.renamePlayer(oldUsername, newUsername);
+        if (!lobbySynced) {
+            userRegistry.changeUsername(currentUser.getId(), oldUsername);
+            responseDispatcher.dispatch(
+                    new ErrorResponse(
+                            request.getContext(),
+                            "RENAME_CONFLICT",
+                            "Could not update username in current lobby/game state."));
+            return;
+        }
+
+        responseDispatcher.dispatch(
+                new ChangeUsernameResponse(
+                        request.getContext(), currentUser.getName(), currentUser.getId()));
+
+        broadcastUsernameChanged(oldUsername, currentUser.getName());
+    }
+
+    private void broadcastUsernameChanged(String oldUsername, String newUsername) {
+        if (sessionManager == null) {
+            return;
+        }
+
+        for (Session session : sessionManager.getAllSessions()) {
+            RequestContext ctx = new RequestContext(session.getId(), 0);
+            SuccessResponse ev =
+                    new SuccessResponse(
+                            ctx,
+                            new ResponseBodyBuilder()
+                                    .param("EVENT", "USERNAME_CHANGED")
+                                    .param("OLD_USERNAME", oldUsername)
+                                    .param("NEW_USERNAME", newUsername)
+                                    .build()) {};
+            responseDispatcher.dispatch(ev);
+        }
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/change_username/ChangeUsernameParser.java

@@ -0,0 +1,15 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.change_username;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.command.parsing.CommandParser;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.PrimitiveRequest;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.accessor.RequestParameterAccessor;
+
+/** Parses CHANGE_USERNAME requests. */
+public class ChangeUsernameParser implements CommandParser<ChangeUsernameRequest> {
+    @Override
+    public ChangeUsernameRequest parse(PrimitiveRequest primitiveRequest) {
+        RequestParameterAccessor accessor =
+                new RequestParameterAccessor(primitiveRequest.parameters());
+        return new ChangeUsernameRequest(primitiveRequest.context(), accessor.require("USERNAME"));
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/change_username/ChangeUsernameRequest.java

@@ -0,0 +1,25 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.change_username;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.Request;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
+
+/** Request used to change the username of the current session user. */
+public class ChangeUsernameRequest extends Request {
+    private final String username;
+
+    /**
+     * @param context request context for responses
+     * @param username desired new username
+     */
+    public ChangeUsernameRequest(RequestContext context, String username) {
+        super(context);
+        this.username = username;
+    }
+
+    /**
+     * @return desired new username
+     */
+    public String getUsername() {
+        return username;
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/change_username/ChangeUsernameResponse.java

@@ -0,0 +1,23 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.change_username;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.UserId;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.SuccessResponse;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.builder.ResponseBodyBuilder;
+
+/** Response for successful username changes. */
+public class ChangeUsernameResponse extends SuccessResponse {
+    /**
+     * @param context request context
+     * @param username current username after the rename operation
+     * @param id user id of renamed user
+     */
+    public ChangeUsernameResponse(RequestContext context, String username, UserId id) {
+        super(
+                context,
+                new ResponseBodyBuilder()
+                        .param("USERNAME", username)
+                        .param("ID", id.value())
+                        .build());
+    }
+}

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/domain/game/GameController.java

@@ -254,4 +254,12 @@ 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 -> {
+            case SHOWDOWN -> state.setPhase(GamePhase.FINISHED);
-                /* nothing */
+            case FINISHED -> {
+                /* game is over */
             }
         }
     }

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

@@ -11,19 +11,15 @@ import java.util.List;
 import java.util.Map;
 
 /**
- * The GameState class encapsulates the entire state of a poker game at any
+ * The GameState class encapsulates the entire state of a poker game at any given moment.
- * given moment.
  *
- * <p>
+ * <p>Important invariants this implementation maintains:
- * Important invariants this implementation maintains:
  *
  * <ul>
- * <li>{@code playerOrder} defines the stable seating/turn order.
+ *   <li>{@code playerOrder} defines the stable seating/turn order.
- * <li>{@code currentBets} always contains an entry for every player in
+ *   <li>{@code currentBets} always contains an entry for every player in {@code playerOrder}.
- * {@code playerOrder}.
+ *   <li>{@code holeCards} maps every player to a mutable list; if not present, it is created on
- * <li>{@code holeCards} maps every player to a mutable list; if not present, it
+ *       demand.
- * is created on
- * demand.
  * </ul>
  */
 public class GameState {
@@ -188,8 +184,7 @@ public class GameState {
     }
 
     /**
-     * Reset bets to 0 for ALL players (do not clear the map). Also resets table
+     * Reset bets to 0 for ALL players (do not clear the map). Also resets table current bet to 0.
-     * current bet to 0.
      */
     public void resetBets() {
         for (PlayerId id : playerOrder) {
@@ -232,8 +227,7 @@ public class GameState {
     // Cards
 
     /**
-     * Gives (overwrites) the two hole cards for the given player. Ensures stable
+     * Gives (overwrites) the two hole cards for the given player. Ensures stable list identity
-     * list identity
      * (important if other code holds references).
      */
     public void giveHoleCards(PlayerId playerId, Card c1, Card c2) {
@@ -293,14 +287,13 @@ public class GameState {
     /**
      * Starts a new hand by resetting the game state for the next round of poker.
      *
-     * <p>
+     * <p>This:
-     * This:
      *
      * <ul>
-     * <li>sets {@code phase=PREFLOP}
+     *   <li>sets {@code phase=PREFLOP}
-     * <li>resets pot/bets/commitments
+     *   <li>resets pot/bets/commitments
-     * <li>clears community + hole cards
+     *   <li>clears community + hole cards
-     * <li>creates &amp; shuffles a new deck
+     *   <li>creates &amp; shuffles a new deck
      * </ul>
      */
     public void startNewHand() {
@@ -336,4 +329,19 @@ 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;
+    }
 }