src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/ServerApp.java

@@ -197,5 +197,19 @@ public class ServerApp {
                                         .JoinLobbyRequest>)
                         new ch.unibas.dmi.dbis.cs108.casono.server.app.commands.lobby.join_lobby
                                 .JoinLobbyHandler(responseDispatcher, lobbyManager, userRegistry));
+
+        // START_GAME registration
+        parserDispatcher.register(
+                "START_GAME",
+                new ch.unibas.dmi.dbis.cs108.casono.server.app.commands.lobby.start_game
+                        .StartGameParser());
+        commandRouter.register(
+                ch.unibas.dmi.dbis.cs108.casono.server.app.commands.lobby.start_game
+                        .StartGameRequest.class,
+                (ch.unibas.dmi.dbis.cs108.casono.server.network.command.execution.CommandHandler<
+                                ch.unibas.dmi.dbis.cs108.casono.server.app.commands.lobby.start_game
+                                        .StartGameRequest>)
+                        new ch.unibas.dmi.dbis.cs108.casono.server.app.commands.lobby.start_game
+                                .StartGameHandler(responseDispatcher, lobbyManager, userRegistry));
     }
 }

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/lobby/start_game/StartGameHandler.java

@@ -0,0 +1,113 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.lobby.start_game;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.app.checks.UserLoggedInCheck;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.GameController;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.engine.GameEngine;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.engine.RoundManager;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.engine.TurnManager;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.player.PlayerId;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.rules.RuleEngine;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.game.state.GameState;
+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;
+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.ErrorResponse;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher.ResponseDispatcher;
+import java.util.ArrayList;
+import java.util.Optional;
+
+/**
+ * Handler for START_GAME: creates a GameEngine+GameController for the lobby and starts the game.
+ */
+public class StartGameHandler extends CommandHandler<StartGameRequest> {
+    private final LobbyManager lobbyManager;
+    private final UserRegistry userRegistry;
+    private static final int DEFAULT_START_CHIPS = 20000;
+
+    public StartGameHandler(
+            ResponseDispatcher responseDispatcher,
+            LobbyManager lobbyManager,
+            UserRegistry userRegistry) {
+        super(responseDispatcher);
+        this.lobbyManager = lobbyManager;
+        this.userRegistry = userRegistry;
+        addCheck(new UserLoggedInCheck(userRegistry));
+    }
+
+    @Override
+    public void execute(StartGameRequest request) {
+        Optional<ch.unibas.dmi.dbis.cs108.casono.server.domain.user.User> opt =
+                userRegistry.getBySessionId(request.getSessionId());
+        if (opt.isEmpty()) {
+            // Guard: UserLoggedInCheck should normally handle this
+            responseDispatcher.dispatch(
+                    new ErrorResponse(
+                            request.getContext(), "USER_NOT_LOGGED_IN", "User not logged in"));
+            return;
+        }
+
+        String username = opt.get().getName();
+
+        // Resolve lobby by provided ID (required)
+        LobbyId lid = LobbyId.of(request.getId());
+        Lobby lobby = lobbyManager.getLobby(lid);
+        if (lobby == null) {
+            responseDispatcher.dispatch(
+                    new ErrorResponse(request.getContext(), "LOBBY_NOT_FOUND", "Lobby not found"));
+            return;
+        }
+
+        // Ensure requester is part of the lobby
+        if (!lobby.getPlayerNames().contains(username)) {
+            responseDispatcher.dispatch(
+                    new ErrorResponse(
+                            request.getContext(), "NOT_IN_LOBBY", "User not in specified lobby"));
+            return;
+        }
+
+        // Prevent double-start
+        if (lobby.getGameController() != null) {
+            responseDispatcher.dispatch(
+                    new ErrorResponse(
+                            request.getContext(),
+                            "ALREADY_STARTED",
+                            "Game has already been started for this lobby"));
+            return;
+        }
+
+        // Basic player count check
+        if (lobby.getPlayerNames().size() < 2) {
+            responseDispatcher.dispatch(
+                    new ErrorResponse(
+                            request.getContext(),
+                            "NOT_ENOUGH_PLAYERS",
+                            "Not enough players to start the game"));
+            return;
+        }
+
+        // Create engine + controller
+        GameState state = new GameState();
+        GameEngine engine =
+                new GameEngine(
+                        state,
+                        new RuleEngine(new ArrayList<>()),
+                        new RoundManager(),
+                        new TurnManager());
+        GameController game = new GameController(engine);
+
+        // Add all players from lobby
+        for (String playerName : lobby.getPlayerNames()) {
+            game.addPlayer(PlayerId.of(playerName), DEFAULT_START_CHIPS);
+        }
+
+        // Start the game and attach to lobby
+        game.startGame();
+        lobby.initGame(game);
+
+        responseDispatcher.dispatch(
+                new StartGameResponse(
+                        request.getContext(), lid.value(), "Game started successfully"));
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/lobby/start_game/StartGameParser.java

@@ -0,0 +1,27 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.lobby.start_game;
+
+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;
+
+/**
+ * Parser for the `START_GAME` command.
+ *
+ * <p>Expected request parameters:
+ *
+ * <ul>
+ *   <li>`ID` (int) — numeric lobby identifier (required)
+ * </ul>
+ *
+ * <p>The parser builds a {@link StartGameRequest} containing the parsed lobby id and the original
+ * request context.
+ */
+public class StartGameParser implements CommandParser<StartGameRequest> {
+    @Override
+    public StartGameRequest parse(PrimitiveRequest primitiveRequest) {
+        RequestParameterAccessor accessor =
+                new RequestParameterAccessor(primitiveRequest.parameters());
+        int id = accessor.require("ID", Integer::parseInt);
+        return new StartGameRequest(primitiveRequest.context(), id);
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/lobby/start_game/StartGameRequest.java

@@ -0,0 +1,35 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.lobby.start_game;
+
+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 to start a game in a specific lobby.
+ *
+ * <p>The `START_GAME` request requires the numeric lobby id parameter `ID` identifying the target
+ * lobby. The request carries the usual {@link RequestContext} (session id, request id) via the base
+ * class.
+ */
+public class StartGameRequest extends Request {
+    private final int id;
+
+    /**
+     * Create a new {@link StartGameRequest}.
+     *
+     * @param context the request context
+     * @param id numeric lobby id to start the game in
+     */
+    public StartGameRequest(RequestContext context, int id) {
+        super(context);
+        this.id = id;
+    }
+
+    /**
+     * Returns the numeric lobby id provided by the client.
+     *
+     * @return lobby id
+     */
+    public int getId() {
+        return id;
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/lobby/start_game/StartGameResponse.java

@@ -0,0 +1,34 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.lobby.start_game;
+
+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.ResponseBody;
+
+/**
+ * Success response for {@code START_GAME} containing the started game's identifier and an
+ * informational message.
+ */
+public class StartGameResponse extends SuccessResponse {
+    /**
+     * Create a standard start-game response with a default success message.
+     *
+     * @param context the request context
+     * @param gameId numeric id of the started game (uses lobby id)
+     */
+    public StartGameResponse(RequestContext context, int gameId) {
+        this(context, gameId, "Game started successfully");
+    }
+
+    /**
+     * Create a start-game response with a custom message.
+     *
+     * @param context the request context
+     * @param gameId numeric id of the started game (uses lobby id)
+     * @param message informational message for the client
+     */
+    public StartGameResponse(RequestContext context, int gameId, String message) {
+        super(
+                context,
+                ResponseBody.builder().param("GAME", gameId).param("MESSAGE", message).build());
+    }
+}