fix: redirect players if host leaves

android/src/main/java/group07/beatbattle/android/firebase/FirestoreSessionRepository.java

@@ -346,7 +346,10 @@ public void listenToSessionState(
                     listener.onFailure(error);
                     return;
                 }
-                if (snapshot == null || !snapshot.exists()) return;
+                if (snapshot == null || !snapshot.exists()) {
+                    listener.onSessionDeleted();
+                    return;
+                }
                 String state = snapshot.getString("state");
                 Long roundLong = snapshot.getLong("currentRound");
                 int currentRound = roundLong != null ? roundLong.intValue() : 0;

core/src/main/java/group07/beatbattle/controller/LeaderboardController.java

@@ -90,6 +90,15 @@ private void launchNextRound() {
     }
 
     public void onBackToMenu() {
+        if (game.isLocalHost()) {
+            String sessionId = game.getLocalSessionId();
+            if (sessionId != null && !sessionId.isBlank()) {
+                game.getFirebaseGateway().deleteSession(sessionId, new FirebaseGateway.DeleteSessionCallback() {
+                    @Override public void onSuccess() {}
+                    @Override public void onFailure(Exception e) {}
+                });
+            }
+        }
         StateManager.getInstance().setState(new StartState(game, new LobbyController(game)));
     }
 

core/src/main/java/group07/beatbattle/controller/LobbyController.java

@@ -7,6 +7,8 @@
 import java.util.List;
 
 import group07.beatbattle.BeatBattle;
+import group07.beatbattle.ecs.Engine;
+import group07.beatbattle.ecs.systems.AudioSystem;
 import group07.beatbattle.firebase.FirebaseGateway;
 import group07.beatbattle.model.GameMode;
 import group07.beatbattle.model.GameSession;
@@ -289,6 +291,15 @@ public void onStateChanged(String state, int currentRound) {
                     }
                 }
 
+                @Override
+                public void onSessionDeleted() {
+                    Gdx.app.postRunnable(() -> {
+                        AudioSystem.getInstance().stopAll();
+                        Engine.getInstance().reset();
+                        StateManager.getInstance().setState(new StartState(game, new LobbyController(game)));
+                    });
+                }
+
                 @Override
                 public void onFailure(Exception exception) {
                     Gdx.app.error("LobbyController",

core/src/main/java/group07/beatbattle/controller/RoundController.java

@@ -89,6 +89,16 @@ public void onRoundExpired() {
     public void onLeaveSession() {
         AudioSystem.getInstance().stop(roundEntity);
         Engine.getInstance().removeEntity(roundEntity);
+        if (game.isLocalHost()) {
+            String sessionId = game.getLocalSessionId();
+            if (sessionId != null && !sessionId.isBlank()) {
+                game.getFirebaseGateway().deleteSession(sessionId, new FirebaseGateway.DeleteSessionCallback() {
+                    @Override public void onSuccess() {}
+                    @Override public void onFailure(Exception e) {}
+                });
+            }
+        }
+
         StateManager.getInstance().setState(new StartState(game, new LobbyController(game)));
     }
 

core/src/main/java/group07/beatbattle/ecs/systems/AudioSystem.java

@@ -51,6 +51,15 @@ public boolean isMuted() {
         return muted;
     }
 
+    /**
+     * Stops any currently playing audio without needing a specific entity reference.
+     * Used when a joiner is redirected to the start screen mid-round because the
+     * host left
+     */
+    public void stopAll() {
+        if (audioPlayer != null) audioPlayer.stop();
+    }
+
     public void dispose() {
         if (audioPlayer != null) audioPlayer.dispose();
     }

core/src/main/java/group07/beatbattle/firebase/FirebaseGateway.java

@@ -132,6 +132,10 @@ interface SessionStateListener {
          *  @param currentRound  current round index stored in Firebase */
         void onStateChanged(String state, int currentRound);
         void onFailure(Exception exception);
+        /**
+         * Called when the session document is deleted from Firestore. If host leaves.
+         */
+        default void onSessionDeleted() {}
     }
 
     interface AnswerCountCallback {

core/src/main/java/group07/beatbattle/view/LobbyView.java

@@ -26,6 +26,8 @@
 import group07.beatbattle.model.GameMode;
 import group07.beatbattle.model.Player;
 import group07.beatbattle.model.services.LobbyService;
+import group07.beatbattle.states.StartState;
+import group07.beatbattle.states.StateManager;
 import group07.beatbattle.ui.components.BackButton;
 import group07.beatbattle.ui.components.RoundSelector;
 import group07.beatbattle.ui.components.SettingsButton;
@@ -165,6 +167,15 @@ public void onFailure(Exception exception) {
                         );
                     }
                 }
+
+                @Override
+                public void onSessionDeleted() {
+                    Gdx.app.postRunnable(() -> {
+                        if (!leavingLobby && !gameStarted) {
+                            StateManager.getInstance().setState(new StartState(game, new LobbyController(game)));
+                        }
+                    });
+                }
 
                 @Override
                 public void onFailure(Exception exception) {