Merge remote-tracking branch 'origin/main' into feat/game-engine

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

@@ -10,15 +10,15 @@ import org.apache.logging.log4j.Logger;
 /**
  * Entry point for the Casono client application. Handles client startup and connection parameters.
  *
- * <p>Standardkonstruktor für die Anwendung.
+ * <p>Default constructor for the application.
  */
 public class ClientApp {
 
     private static final Logger LOGGER = LogManager.getLogger(ClientApp.class);
 
-    /** Standardkonstruktor. */
+    /** Default constructor. */
     public ClientApp() {
-        // Standardkonstruktor
+        // Default constructor
     }
 
     /**

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

@@ -6,13 +6,13 @@ import javafx.application.Application;
 /**
  * Launcher for the Casono main UI.
  *
- * <p>Standardkonstruktor für die Anwendung.
+ * <p>Default constructor for the application.
  */
 public class Launcher {
 
-    /** Standardkonstruktor. */
+    /** Default constructor. */
     public Launcher() {
-        // Standardkonstruktor
+        // Default constructor
     }
 
     /**

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

@@ -41,6 +41,11 @@ public class ChatController {
         chatScrollPane.vvalueProperty().bind(chatVBox.heightProperty());
     }
 
+    /** Standardkonstruktor. Wird von FXML verwendet. */
+    public ChatController() {
+        // default constructor for FXML
+    }
+
     /**
      * Diese Methode wird vom Senden-Button oder Enter ausgelöst. Sie gibt die eigene Nachricht an
      * das Netzwerkprotokoll weiter.

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

@@ -15,11 +15,22 @@ import javafx.scene.layout.VBox;
  */
 public class CasinoGameController {
 
+    /** Standardkonstruktor. Wird von FXML verwendet. */
+    public CasinoGameController() {
+        // default constructor for FXML
+    }
+
     @FXML private Label welcomeText;
     @FXML private VBox casinoTable;
 
     // TODO: Test-Logik: wird durch echte Spielinteraktionen ersetzt,
     // sobald die GameEngine fertig ist
+
+    /**
+     * Temporäre Test-Methode, die bei Klick auf den Tisch eine Platzhalteraktion ausführt.
+     *
+     * <p>Wird in der finalen Implementierung durch die Spiel-Logik ersetzt.
+     */
     @FXML
     public void onTableClick() {
         welcomeText.setText("Einsatz akzeptiert!");

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

@@ -17,6 +17,11 @@ import javafx.stage.Stage;
  */
 public class CasinoGameUI extends Application {
 
+    /** Standardkonstruktor. */
+    public CasinoGameUI() {
+        // default no-arg constructor
+    }
+
     private static final int DEFAULT_WIDTH = 1200;
     private static final int DEFAULT_HEIGHT = 800;
 
@@ -29,7 +34,7 @@ public class CasinoGameUI extends Application {
     @Override
     public void start(Stage stage) throws IOException {
         FXMLLoader fxmlLoader =
-                new FXMLLoader(CasinoGameUI.class.getResource("/ui-structure/casinogameui.fxml"));
+                new FXMLLoader(CasinoGameUI.class.getResource("/ui-structure/Casinogameui.fxml"));
         Scene scene = new Scene(fxmlLoader.load(), DEFAULT_WIDTH, DEFAULT_HEIGHT);
         stage.setTitle("Casono (GAME)");
 

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

@@ -27,6 +27,8 @@ import javafx.scene.shape.Rectangle;
 import javafx.scene.web.WebEngine;
 import javafx.scene.web.WebView;
 import javafx.stage.Stage;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 
 /**
  * Experimenteller integrierter Browser für Casono.
@@ -50,13 +52,17 @@ import javafx.stage.Stage;
  */
 public class CasinoBrowserController {
 
+    /** Standardkonstruktor. Initialisiert den CasinoBrowserController. */
+    public CasinoBrowserController() {
+        // Intentionally left blank; controller initialization is FXML-driven.
+    }
+
     private static final Set<String> TRUSTED_DOMAINS = new HashSet<>();
 
     private static final CookieManager COOKIE_MANAGER =
             new CookieManager(null, CookiePolicy.ACCEPT_ORIGINAL_SERVER);
 
-    private static final org.apache.logging.log4j.Logger LOGGER =
-            org.apache.logging.log4j.LogManager.getLogger(CasinoBrowserController.class);
+    private static final Logger LOGGER = LogManager.getLogger(CasinoBrowserController.class);
 
     private static final int LOGO_HEIGHT = 40;
     private static final int CORNER_RADIUS = 40;
@@ -354,8 +360,9 @@ public class CasinoBrowserController {
         fwdBtn.getStyleClass().add("gray-button");
         fwdBtn.setOnAction(
                 e -> {
-                    if (engine.getHistory().getCurrentIndex()
-                            < engine.getHistory().getEntries().size() - 1) {
+                    int currentIndex = engine.getHistory().getCurrentIndex();
+                    int lastIndex = engine.getHistory().getEntries().size() - 1;
+                    if (currentIndex < lastIndex) {
                         engine.getHistory().go(1);
                     }
                 });
@@ -423,7 +430,7 @@ public class CasinoBrowserController {
 
         Scene scene = new Scene(root, WINDOW_WIDTH, WINDOW_HEIGHT);
 
-        var css = CasinoBrowserController.class.getResource("/ui-structure/casinogameui.css");
+        var css = CasinoBrowserController.class.getResource("/ui-structure/Casinogameui.css");
 
         if (css != null) {
             scene.getStylesheets().add(css.toExternalForm());
@@ -512,10 +519,11 @@ public class CasinoBrowserController {
 
         alert.setTitle("Unbekannte Website");
         alert.setHeaderText("Diese Website ist nicht bekannt");
-        alert.setContentText(
+        String content =
                 host
-                        + "\n\nDiese Seite ist nicht vom "
-                        + "Casono Browser verifiziert.\nMöchten Sie sie trotzdem öffnen?");
+                        + "\n\nDiese Seite ist nicht vom Casono Browser verifiziert.\n"
+                        + "Möchten Sie sie trotzdem öffnen?";
+        alert.setContentText(content);
 
         var stream = CasinoBrowserController.class.getResourceAsStream(LOGO_PATH);
         Image logo = new Image(stream);

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

@@ -1,12 +1,14 @@
 package ch.unibas.dmi.dbis.cs108.casono.client.ui.gameui.gameuicomponents;
 
-import javafx.application.Platform;
+import ch.unibas.dmi.dbis.cs108.casono.client.ui.lobbyui.Casinomainui;
 import javafx.fxml.FXML;
 import javafx.scene.control.TextField;
 import javafx.scene.input.KeyCode;
 import javafx.scene.input.KeyEvent;
 import javafx.scene.input.MouseEvent;
 import javafx.scene.layout.HBox;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 
 /**
  * Controller für die interaktive Taskleiste innerhalb der Poker-UI.
@@ -16,8 +18,12 @@ import javafx.scene.layout.HBox;
  */
 public class TaskbarController {
 
-    private static final org.apache.logging.log4j.Logger LOGGER =
-            org.apache.logging.log4j.LogManager.getLogger(CasinoBrowserController.class);
+    /** Standardkonstruktor. Wird von FXML verwendet. */
+    public TaskbarController() {
+        // default constructor for FXML
+    }
+
+    private static final Logger LOGGER = LogManager.getLogger(CasinoBrowserController.class);
 
     @FXML private HBox taskbar;
     @FXML private TextField taskbarInput;
@@ -92,15 +98,21 @@ public class TaskbarController {
         processBet();
     }
 
-    /**
-     * Wird aufgerufen, wenn der Exit-Button in der Taskleiste gedrückt wird.
-     *
-     * <p>TODO: Logik implementieren, um zur Lobby zurückzukehren, ohne die gesamte Anwendung zu
-     * schließen (kein System.exit/Platform.exit).
-     */
     @FXML
     private void onExitButtonClick() {
-        Platform.exit();
+        javafx.application.Platform.runLater(
+                () -> {
+                    // Close game stage
+                    javafx.stage.Stage currentStage =
+                            (javafx.stage.Stage) taskbar.getScene().getWindow();
+                    currentStage.close();
+                    // Lobby-UI starten
+                    try {
+                        new Casinomainui().start(new javafx.stage.Stage());
+                    } catch (Exception e) {
+                        LOGGER.error("Fehler beim Starten der Lobby-UI: {}", e.getMessage());
+                    }
+                });
     }
 
     /**

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

@@ -10,13 +10,13 @@ import javafx.stage.Stage;
 /**
  * JavaFX Application class for the Casono main UI.
  *
- * <p>Standardkonstruktor für die Anwendung.
+ * <p>Default constructor for the application.
  */
 public class Casinomainui extends Application {
 
-    /** Standardkonstruktor. */
+    /** Default constructor. */
     public Casinomainui() {
-        // Standardkonstruktor
+        // Default constructor
     }
 
     private static final int SCENE_WIDTH = 1200;

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

@@ -28,6 +28,7 @@ public class CasinomainuiController {
     private LobbyButtonGridManager gridManager;
     private int nextButtonId = 1;
 
+    /** Default constructor for dependency injection by FXMLLoader. */
     public CasinomainuiController() {
         // Default constructor
     }
@@ -39,7 +40,7 @@ public class CasinomainuiController {
         subtitleLabel.setText("Texas Hold'em Poker");
         logoView.setImage(new Image(getClass().getResource("/images/logo.png").toExternalForm()));
 
-        translationManager = new LobbyButtonTranslationManager();
+        translationManager = LobbyButtonTranslationManager.getInstance();
         gridManager =
                 new LobbyButtonGridManager(new javafx.scene.layout.GridPane(), translationManager);
         casinoTable.getChildren().clear();
@@ -57,7 +58,7 @@ public class CasinomainuiController {
     @FXML
     public void handleCreateLobbyButton() {
         if (translationManager.isFull()) {
-            LOGGER.warn("Grid voll! Keine weiteren Lobbys moeglich.");
+            LOGGER.warn("Grid is full! No more lobbies available.");
             return;
         }
         int buttonId = nextButtonId++;
@@ -67,7 +68,7 @@ public class CasinomainuiController {
             LOGGER.info("ButtonID: {}, LobbyID: {}", buttonId, lobbyId);
             gridManager.renderLobbyButtons();
         } catch (Exception e) {
-            LOGGER.error("Fehler beim Hinzufügen: {}", e.getMessage());
+            LOGGER.error("Error while adding lobby button: {}", e.getMessage());
         }
     }
 }

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

@@ -17,6 +17,8 @@ import org.apache.logging.log4j.Logger;
  * ButtonID to LobbyID.
  */
 public class LobbyButtonGridManager {
+    private static final double BUTTON_WIDTH_MARGIN = 20.0;
+    private static final double BUTTON_MIN_SIZE = 10.0;
     private static final Logger LOGGER = LogManager.getLogger(LobbyButtonGridManager.class);
 
     /** GridPane for the button grid. */
@@ -46,7 +48,8 @@ public class LobbyButtonGridManager {
     public LobbyButtonGridManager(
             GridPane gridPane, LobbyButtonTranslationManager translationManager) {
         this.gridPane = gridPane;
-        this.translationManager = translationManager;
+        // Singleton immer verwenden
+        this.translationManager = LobbyButtonTranslationManager.getInstance();
     }
 
     /**
@@ -65,8 +68,21 @@ public class LobbyButtonGridManager {
             int buttonId = entry.getKey();
             Button btn = new Button();
             btn.setId("lobbyBtn-" + buttonId);
-            btn.setGraphic(
-                    new ImageView(new Image(getClass().getResourceAsStream(BUTTON_IMAGE_PATH))));
+            ImageView imageView =
+                    new ImageView(new Image(getClass().getResourceAsStream(BUTTON_IMAGE_PATH)));
+            imageView.setPreserveRatio(true);
+            // Dynamische Breite: Bindung an die Zellengröße
+            imageView
+                    .fitWidthProperty()
+                    .bind(gridPane.widthProperty().divide(COLS).subtract(BUTTON_WIDTH_MARGIN));
+            imageView.setSmooth(true);
+            btn.setGraphic(imageView);
+            btn.setMaxWidth(Double.MAX_VALUE);
+            btn.setMaxHeight(Double.MAX_VALUE);
+            btn.setMinWidth(BUTTON_MIN_SIZE);
+            btn.setMinHeight(BUTTON_MIN_SIZE);
+            GridPane.setHgrow(btn, javafx.scene.layout.Priority.ALWAYS);
+            GridPane.setVgrow(btn, javafx.scene.layout.Priority.ALWAYS);
             btn.setOnAction(
                     e -> {
                         Integer lobbyId = translationManager.getLobbyIdForButton(buttonId);
@@ -99,8 +115,22 @@ public class LobbyButtonGridManager {
      * @param lobbyId The lobbyId to join
      */
     public void joinLobby(int lobbyId) {
-        // TODO: Replace with actual join logic
+        // Game-UI starten und Lobby-UI schließen
         LOGGER.info("Joining lobby: {}", lobbyId);
+        javafx.application.Platform.runLater(
+                () -> {
+                    // Lobby-Stage schließen
+                    javafx.stage.Stage currentStage =
+                            (javafx.stage.Stage) gridPane.getScene().getWindow();
+                    currentStage.close();
+                    // Game-UI starten
+                    try {
+                        new ch.unibas.dmi.dbis.cs108.casono.client.ui.gameui.CasinoGameUI()
+                                .start(new javafx.stage.Stage());
+                    } catch (Exception e) {
+                        LOGGER.error("Fehler beim Starten der Game-UI: {}", e.getMessage());
+                    }
+                });
     }
 
     /**

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

@@ -4,36 +4,53 @@ import java.util.HashMap;
 import java.util.Map;
 
 /**
- * Verwaltet das Mapping zwischen Button-IDs und Lobby-IDs rein im Speicher. Keine Dateioperationen,
- * nur Laufzeitdatenstruktur.
+ * Manages the mapping between Button IDs and Lobby IDs in memory only. No file operations,
+ * runtime-only data structure.
  */
 public class LobbyButtonTranslationManager {
-    /** Maximale Anzahl an Buttons/Lobbys */
+
+    // Singleton instance
+    private static LobbyButtonTranslationManager instance;
+
+    // Singleton access
+    /**
+     * Returns the singleton instance of the manager.
+     *
+     * @return the single instance of {@code LobbyButtonTranslationManager}
+     */
+    public static LobbyButtonTranslationManager getInstance() {
+        if (instance == null) {
+            instance = new LobbyButtonTranslationManager();
+        }
+        return instance;
+    }
+
+    /** Maximum number of buttons/lobbies */
     private static final int MAX_BUTTONS = 8;
 
-    /** Zuordnung ButtonID → LobbyID */
+    /** Mapping ButtonID → LobbyID */
     private final Map<Integer, Integer> buttonIdToLobbyId = new HashMap<>();
 
-    /** Konstruktor: initialisiert die Zuordnung leer. */
-    public LobbyButtonTranslationManager() {
-        // Zuordnung bleibt leer beim Start
+    /** Private constructor for the singleton pattern */
+    private LobbyButtonTranslationManager() {
+        // Mapping is empty at startup
     }
 
     /**
-     * Prüft, ob das Grid voll ist (MAX_BUTTONS erreicht).
+     * Checks whether the grid is full (MAX_BUTTONS reached).
      *
-     * @return true, wenn Grid voll; sonst false
+     * @return true if the grid is full; otherwise false
      */
     public boolean isFull() {
         return buttonIdToLobbyId.size() >= MAX_BUTTONS;
     }
 
     /**
-     * Fügt eine Zuordnung ButtonID → LobbyID hinzu.
+     * Adds a mapping ButtonID → LobbyID.
      *
-     * @param buttonId Die ID des Buttons
-     * @param lobbyId Die ID der Lobby
-     * @throws Exception wenn das Grid voll ist
+     * @param buttonId the ID of the button
+     * @param lobbyId the ID of the lobby
+     * @throws Exception when the grid is full
      */
     public void addLobbyButton(int buttonId, int lobbyId) throws Exception {
         if (isFull()) {
@@ -43,28 +60,28 @@ public class LobbyButtonTranslationManager {
     }
 
     /**
-     * Entfernt eine Zuordnung für die gegebene ButtonID.
+     * Removes the mapping for the given ButtonID.
      *
-     * @param buttonId Die ID des zu entfernenden Buttons
+     * @param buttonId the ID of the button to remove
      */
     public void removeLobbyButton(int buttonId) {
         buttonIdToLobbyId.remove(buttonId);
     }
 
     /**
-     * Gibt die LobbyID für eine gegebene ButtonID zurück.
+     * Returns the LobbyID for a given ButtonID.
      *
-     * @param buttonId Die ButtonID
-     * @return Die zugehoerige LobbyID oder null, falls nicht vorhanden
+     * @param buttonId the ButtonID
+     * @return the associated LobbyID or null if not present
      */
     public Integer getLobbyIdForButton(int buttonId) {
         return buttonIdToLobbyId.get(buttonId);
     }
 
     /**
-     * Gibt die gesamte Zuordnung ButtonID → LobbyID zurück.
+     * Returns the full mapping ButtonID → LobbyID.
      *
-     * @return Map aller Zuordnungen
+     * @return Map of all mappings
      */
     public Map<Integer, Integer> getButtonIdToLobbyId() {
         return buttonIdToLobbyId;

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

@@ -1,5 +1,11 @@
 package ch.unibas.dmi.dbis.cs108.casono.server;
 
+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;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping.PingHandler;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping.PingParser;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping.PingRequest;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.UserCleanupJob;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.UserRegistry;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.NetworkManager;
@@ -7,6 +13,7 @@ import ch.unibas.dmi.dbis.cs108.casono.server.network.command.execution.CommandR
 import ch.unibas.dmi.dbis.cs108.casono.server.network.command.parsing.CommandParserDispatcher;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.events.DisconnectEvent;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.events.EventBus;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher.ResponseDispatcher;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionDisconnectJob;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionManager;
 import java.time.Duration;
@@ -58,6 +65,31 @@ public class ServerApp {
                 SESSION_DISCONNECT_JOB_PERIOD,
                 TimeUnit.SECONDS);
 
+        ResponseDispatcher responseDispatcher = new ResponseDispatcher(sessionManager);
+
+        registerCommands(dispatcher, router, responseDispatcher, userRegistry);
+
         networkManager.start();
     }
+
+    /**
+     * Registers command parsers and handlers.
+     *
+     * @param parserDispatcher the dispatcher responsible for parsing incoming commands
+     * @param commandRouter the router that dispatches parsed commands to appropriate handlers
+     * @param responseDispatcher the dispatcher responsible for sending responses back to clients
+     */
+    private static void registerCommands(
+            CommandParserDispatcher parserDispatcher,
+            CommandRouter commandRouter,
+            ResponseDispatcher responseDispatcher,
+            UserRegistry userRegistry) {
+        parserDispatcher.register("PING", new PingParser());
+        commandRouter.register(PingRequest.class, new PingHandler(responseDispatcher));
+
+        parserDispatcher.register("CHECK_USERNAME", new CheckUsernameParser());
+        commandRouter.register(
+                CheckUsernameRequest.class,
+                new CheckUsernameHandler(responseDispatcher, userRegistry));
+    }
 }

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/check_nick/CheckUsernameHandler.java

@@ -0,0 +1,44 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick;
+
+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.response.dispatcher.ResponseDispatcher;
+import java.util.Optional;
+
+/** Handles {@link CheckUsernameRequest}s to check whether a username is available. */
+public class CheckUsernameHandler implements CommandHandler<CheckUsernameRequest> {
+    private final ResponseDispatcher responseDispatcher;
+    private final UserRegistry userRegistry;
+
+    /**
+     * Creates a new handler for checking username availability.
+     *
+     * @param responseDispatcher the dispatcher used to send the response
+     * @param userRegistry the registry used to look up existing users
+     */
+    public CheckUsernameHandler(ResponseDispatcher responseDispatcher, UserRegistry userRegistry) {
+        this.responseDispatcher = responseDispatcher;
+        this.userRegistry = userRegistry;
+    }
+
+    /**
+     * Executes the username availability check for the given request.
+     *
+     * <p>If no user exists for the requested username, the username is reported as {@link
+     * UsernameAvailability#FREE}; otherwise, it is reported as {@link UsernameAvailability#TAKEN}.
+     *
+     * @param request the request to execute
+     */
+    @Override
+    public void execute(CheckUsernameRequest request) {
+        Optional<User> user = userRegistry.getByUsername(request.getUsername());
+        UsernameAvailability availability;
+        if (user.isEmpty()) {
+            availability = UsernameAvailability.FREE;
+        } else {
+            availability = UsernameAvailability.TAKEN;
+        }
+        responseDispatcher.dispatch(new CheckUsernameResponse(request.getContext(), availability));
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/check_nick/CheckUsernameParser.java

@@ -0,0 +1,21 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick;
+
+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 a primitive request into a {@link CheckUsernameRequest}. */
+public class CheckUsernameParser implements CommandParser<CheckUsernameRequest> {
+    /**
+     * Extracts the required {@code USERNAME} parameter from the incoming request.
+     *
+     * @param primitiveRequest the request to parse
+     * @return {@link CheckUsernameRequest} containing the username
+     */
+    @Override
+    public CheckUsernameRequest parse(PrimitiveRequest primitiveRequest) {
+        RequestParameterAccessor accessor =
+                new RequestParameterAccessor(primitiveRequest.parameters());
+        return new CheckUsernameRequest(primitiveRequest.context(), accessor.require("USERNAME"));
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/check_nick/CheckUsernameRequest.java

@@ -0,0 +1,30 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick;
+
+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 implementation used to check whether a username is available or already taken */
+public class CheckUsernameRequest extends Request {
+    private final String username;
+
+    /**
+     * Constructs a new CheckUsernameRequest with the given context and username to check
+     *
+     * @param context the {@link RequestContext} containing information for responding to the
+     *     request
+     * @param username the username to check for availability
+     */
+    public CheckUsernameRequest(RequestContext context, String username) {
+        super(context);
+        this.username = username;
+    }
+
+    /**
+     * Returns the provided username in the request
+     *
+     * @return username to check
+     */
+    public String getUsername() {
+        return username;
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/check_nick/CheckUsernameResponse.java

@@ -0,0 +1,18 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick;
+
+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 indicating the availability status of a username check. */
+public class CheckUsernameResponse extends SuccessResponse {
+    /**
+     * Creates a new response to respond to the username availability check to
+     *
+     * @param context the {@link RequestContext} associated with the request
+     * @param availability the availability status of the requested username
+     */
+    public CheckUsernameResponse(RequestContext context, UsernameAvailability availability) {
+        super(context, new ResponseBodyBuilder().param("STATUS", availability).build());
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/check_nick/UsernameAvailability.java

@@ -0,0 +1,10 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick;
+
+/** Represents the availability status of a username */
+enum UsernameAvailability {
+    /** Username is available */
+    FREE,
+
+    /** Username is already in use */
+    TAKEN
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/ping/PingHandler.java

@@ -0,0 +1,29 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping;
+
+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;
+
+/** Handler for {@link PingRequest}. */
+public class PingHandler implements CommandHandler<PingRequest> {
+    private final ResponseDispatcher responseDispatcher;
+
+    /**
+     * Create a new PingHandler to execute {@link PingRequest}s
+     *
+     * @param responseDispatcher dispatcher used to send responses back to clients
+     */
+    public PingHandler(ResponseDispatcher responseDispatcher) {
+        this.responseDispatcher = responseDispatcher;
+    }
+
+    /**
+     * Execute the ping request.
+     *
+     * @param request the ping request to handle
+     */
+    @Override
+    public void execute(PingRequest request) {
+        responseDispatcher.dispatch(new OkResponse(request.getContext()));
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/ping/PingParser.java

@@ -0,0 +1,22 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.command.parsing.CommandParser;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.PrimitiveRequest;
+
+/**
+ * Parser for the Ping command.
+ *
+ * <p>Converts a low-level {@link PrimitiveRequest} into a {@link PingRequest}.
+ */
+public class PingParser implements CommandParser<PingRequest> {
+    /**
+     * Parse the given primitive request into a {@link PingRequest}.
+     *
+     * @param primitiveRequest the raw request to parse
+     * @return {@link PingRequest}
+     */
+    @Override
+    public PingRequest parse(PrimitiveRequest primitiveRequest) {
+        return new PingRequest(primitiveRequest.context());
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/ping/PingRequest.java

@@ -0,0 +1,19 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.ping;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.Request;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
+
+/**
+ * Represents a "PING" request sent by a client to check server availability and keep the connection
+ * alive.
+ */
+public class PingRequest extends Request {
+    /**
+     * Constructs a new PingRequest with the given context.
+     *
+     * @param context the request context associated with this request
+     */
+    public PingRequest(RequestContext context) {
+        super(context);
+    }
+}

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

@@ -86,15 +86,38 @@ public class UserRegistry {
     }
 
     /**
-     * Looks up a user by their session ID.
+     * Looks up a user by their {@link SessionId}.
      *
-     * @param sessionId the session ID to look up
-     * @return an Optional containing the user, or empty if no user is associated with this session
+     * @param sessionId the SessionId to look up
+     * @return an Optional containing the {@link User}, or empty if no user is associated with this
+     *     SessionId
      */
-    public Optional<User> findBySessionId(SessionId sessionId) {
+    public Optional<User> getBySessionId(SessionId sessionId) {
         return Optional.ofNullable(bySessionId.get(sessionId));
     }
 
+    /**
+     * Looks up a user by their {@link UserId}.
+     *
+     * @param userId the UserId to look up
+     * @return an Optional containing the {@link User}, or empty if no user is associated with this
+     *     UserId
+     */
+    public Optional<User> getByUserId(UserId userId) {
+        return Optional.ofNullable(byId.get(userId));
+    }
+
+    /**
+     * Looks up a user by their username.
+     *
+     * @param username the username to look up
+     * @return an Optional containing the {@link User}, or empty if no user is associated with this
+     *     username
+     */
+    public Optional<User> getByUsername(String username) {
+        return Optional.ofNullable(byName.get(username));
+    }
+
     /**
      * Returns all currently registered users.
      *

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/command/parsing/CommandParser.java

@@ -7,12 +7,12 @@ import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.Request;
  * Parser to convert the PrimitiveRequest to a Request and performing checks for required fields and
  * data types
  */
-public interface CommandParser {
+public interface CommandParser<T extends Request> {
     /**
      * Parses the provided PrimitiveRequest into a command-specific request
      *
      * @param primitiveRequest
      * @return
      */
-    Request parse(PrimitiveRequest primitiveRequest);
+    T parse(PrimitiveRequest primitiveRequest);
 }

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/protocol/response/ErrorResponse.java

@@ -1,23 +1,20 @@
 package ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response;
 
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.builder.ResponseBody;
-import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionId;
 
 /** Response representing an error outcome for a client's request. */
 public class ErrorResponse extends Response {
     /**
      * Construct an error response with a code and message.
      *
-     * @param sessionId the target session id
-     * @param requestId the originating request id
+     * @param context the RequestContext of the request
      * @param errorCode a short error code identifying the failure
      * @param errorMessage a human readable error message
      */
-    public ErrorResponse(
-            SessionId sessionId, int requestId, String errorCode, String errorMessage) {
+    public ErrorResponse(RequestContext context, String errorCode, String errorMessage) {
         super(
-                sessionId,
-                requestId,
+                context,
                 ResponseBody.builder().param("CODE", errorCode).param("MSG", errorMessage).build());
     }
 

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/protocol/response/OkResponse.java

@@ -1,7 +1,7 @@
 package ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response;
 
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.builder.ResponseBody;
-import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionId;
 
 /**
  * A simple success response with an empty body.
@@ -12,10 +12,9 @@ public class OkResponse extends SuccessResponse {
     /**
      * Create a minimal successful response (no body content).
      *
-     * @param sessionId the target session id
-     * @param requestId the originating request id
+     * @param context the RequestContext of the request
      */
-    public OkResponse(SessionId sessionId, int requestId) {
-        super(sessionId, requestId, ResponseBody.builder().build());
+    public OkResponse(RequestContext context) {
+        super(context, ResponseBody.builder().build());
     }
 }

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/protocol/response/Response.java

@@ -1,24 +1,22 @@
 package ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response;
 
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.builder.ResponseBody;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionId;
 
 /** Abstract base class for all server responses sent to clients. */
 public abstract class Response {
-    private final SessionId sessionId;
-    private final int requestId;
+    private final RequestContext context;
     private final ResponseBody body;
 
     /**
      * Create a new {@code Response}.
      *
-     * @param sessionId the id of the session this response targets
-     * @param requestId the request identifier this response corresponds to
+     * @param context the RequestContext of the request
      * @param body the structured response body
      */
-    protected Response(SessionId sessionId, int requestId, ResponseBody body) {
-        this.sessionId = sessionId;
-        this.requestId = requestId;
+    protected Response(RequestContext context, ResponseBody body) {
+        this.context = context;
         this.body = body;
     }
 
@@ -30,12 +28,12 @@ public abstract class Response {
     public abstract String prefix();
 
     /**
-     * Returns the session id that should receive this response.
+     * Returns the session id of the session that should receive this response.
      *
      * @return the target {@link SessionId}
      */
     public SessionId getSessionId() {
-        return sessionId;
+        return context.sessionId();
     }
 
     /**
@@ -44,7 +42,7 @@ public abstract class Response {
      * @return the numeric request id
      */
     public int getRequestId() {
-        return requestId;
+        return context.requestId();
     }
 
     /**

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/protocol/response/SuccessResponse.java

@@ -1,7 +1,7 @@
 package ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response;
 
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.builder.ResponseBody;
-import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionId;
 
 /**
  * Abstract {@link Response} specialization indicating a successful outcome.
@@ -13,12 +13,11 @@ public abstract class SuccessResponse extends Response {
     /**
      * Create a successful response with the provided body.
      *
-     * @param sessionId the session id this response targets
-     * @param requestId the originating request id
+     * @param context the RequestContext of the request
      * @param body the response body
      */
-    protected SuccessResponse(SessionId sessionId, int requestId, ResponseBody body) {
-        super(sessionId, requestId, body);
+    protected SuccessResponse(RequestContext context, ResponseBody body) {
+        super(context, body);
     }
 
     /**

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/protocol/response/dispatcher/ResponseDispatchException.java

@@ -0,0 +1,7 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher;
+
+public class ResponseDispatchException extends RuntimeException {
+    public ResponseDispatchException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/protocol/response/dispatcher/ResponseDispatcher.java

@@ -27,12 +27,17 @@ public class ResponseDispatcher {
      * the target session's response queue.
      *
      * @param response the response to dispatch
-     * @throws InterruptedException if the thread is interrupted while waiting to enqueue the
-     *     primitive response
+     * @throws ResponseDispatchException wraps any exceptions that occur during dispatching, such as
+     *     the {@link InterruptedException}
      */
-    public void dispatch(Response response) throws InterruptedException {
+    public void dispatch(Response response) {
         PrimitiveResponse primitiveResponse = ResponseEncoder.encode(response);
         Session session = sessionManager.getSessionById(response.getSessionId());
-        session.getResponseQueue().put(primitiveResponse);
+        try {
+            session.getResponseQueue().put(primitiveResponse);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new ResponseDispatchException("Interrupted while dispatching response", e);
+        }
     }
 }

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/sessions/SessionReader.java

@@ -12,8 +12,10 @@ import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.Primitive
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RawRequest;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.Request;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.accessor.MissingParameterException;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.ErrorResponse;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.PrimitiveResponse;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher.ResponseDispatchException;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.dispatcher.ResponseEncoder;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.transport.RawPacket;
 import ch.unibas.dmi.dbis.cs108.casono.server.network.transport.TransportLayer;
@@ -46,11 +48,13 @@ public class SessionReader implements Runnable {
         while (!Thread.currentThread().isInterrupted()) {
             RawPacket rawPacket = null;
             RawRequest rawRequest = null;
+            RequestContext requestContext = null;
             try {
                 // Step 1: Read from transport
                 rawPacket = transport.read();
                 session.updateLastInboundActivity();
                 logger.debug("Recieved: {}", rawPacket);
+                requestContext = new RequestContext(session.getId(), rawPacket.requestId());
 
                 // Step 2: Syntax validation and conversion into transport object
                 rawRequest = ProtocolParser.parse(rawPacket.payload());
@@ -58,9 +62,7 @@ public class SessionReader implements Runnable {
 
                 PrimitiveRequest primitiveRequest =
                         new PrimitiveRequest(
-                                new RequestContext(session.getId(), rawPacket.requestId()),
-                                rawRequest.command(),
-                                rawRequest.parameters());
+                                requestContext, rawRequest.command(), rawRequest.parameters());
                 logger.debug("Converted to {}", primitiveRequest);
 
                 // Step 3: Parse into Request and execute Request
@@ -76,8 +78,7 @@ public class SessionReader implements Runnable {
 
                 sendErrorResponse(
                         new ErrorResponse(
-                                session.getId(),
-                                rawPacket.requestId(),
+                                requestContext,
                                 "PARSING_ERROR",
                                 "Error occured during parsing. Likely due to malformed payload."));
 
@@ -85,11 +86,23 @@ public class SessionReader implements Runnable {
                 logger.error("Recieved unknown command '{}' from client", rawRequest.command(), e);
                 sendErrorResponse(
                         new ErrorResponse(
-                                session.getId(),
-                                rawPacket.requestId(),
+                                requestContext,
                                 "UNKNOWN_COMMAND",
                                 "This command is unknown to the server."));
 
+            } catch (ResponseDispatchException e) {
+                logger.error(
+                        "Unexpected ResponseDispatchException exception while dispatching request",
+                        e);
+
+            } catch (MissingParameterException e) {
+                logger.error(
+                        "Recieved request for command '{}' was missing the '{}' parameter",
+                        rawRequest.command(),
+                        e.getParameterKey());
+                sendErrorResponse(
+                        new ErrorResponse(requestContext, "MISSING_PARAMETER", e.getMessage()));
+
             } catch (IOException e) {
                 logger.error("Unexpected IO exception while reading from transport", e);
 
@@ -97,8 +110,7 @@ public class SessionReader implements Runnable {
                 logger.error("Unexpected RuntimeException occured", e);
                 sendErrorResponse(
                         new ErrorResponse(
-                                session.getId(),
-                                rawPacket.requestId(),
+                                requestContext,
                                 "INTERNAL_ERROR",
                                 "Unexpected internal server error occured."));
             }