feat(messaging): push notifications for incoming messages (#104)

- Add NotificationHelper with channel creation, grouped notifications,
  and deep-link PendingIntent into chat
- Trigger notification from MessageRepositoryImpl on WebSocket NewMessage
- Active-chat suppression in ChatViewModel (no notification for current chat)
- Deep-link from notification tap: MainActivity handles intent extras,
  MainScreen navigates to correct Chat screen
- Add POST_NOTIFICATIONS permission to AndroidManifest
- Add notification icon drawable (ic_notification_message)
- Add unit tests for notification suppression logic
- Fix pre-existing test compilation (SyncServiceImplTest missing authEventBus)

app/src/main/AndroidManifest.xml

@@ -2,6 +2,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android">
 
     <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
     <uses-permission android:name="android.permission.REQUEST_INSTALL_PACKAGES" />
 
     <application

app/src/main/java/de/bollwerk/app/BollwerkApp.kt

@@ -2,6 +2,16 @@ package de.bollwerk.app
 
 import android.app.Application
 import dagger.hilt.android.HiltAndroidApp
+import de.bollwerk.app.notification.NotificationHelper
+import javax.inject.Inject
 
 @HiltAndroidApp
-class BollwerkApp : Application()
+class BollwerkApp : Application() {
+
+    @Inject internal lateinit var notificationHelper: NotificationHelper
+
+    override fun onCreate() {
+        super.onCreate()
+        notificationHelper.createNotificationChannel()
+    }
+}

app/src/main/java/de/bollwerk/app/MainActivity.kt

@@ -1,5 +1,6 @@
 package de.bollwerk.app
 
+import android.content.Intent
 import android.os.Bundle
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
@@ -12,8 +13,12 @@ import androidx.lifecycle.lifecycleScope
 import dagger.hilt.android.AndroidEntryPoint
 import de.bollwerk.app.domain.usecase.EnsureKeyPairUseCase
 import de.bollwerk.app.domain.usecase.SeedDatabaseUseCase
+import de.bollwerk.app.notification.NotificationHelper
 import de.bollwerk.app.ui.MainScreen
 import de.bollwerk.app.ui.theme.BollwerkTheme
+import kotlinx.coroutines.flow.MutableSharedFlow
+import kotlinx.coroutines.flow.SharedFlow
+import kotlinx.coroutines.flow.asSharedFlow
 import kotlinx.coroutines.launch
 import javax.inject.Inject
 
@@ -23,19 +28,41 @@ class MainActivity : ComponentActivity() {
     @Inject internal lateinit var seedDatabaseUseCase: SeedDatabaseUseCase
     @Inject internal lateinit var ensureKeyPairUseCase: EnsureKeyPairUseCase
 
+    private val _chatNavigationEvents = MutableSharedFlow<ChatDeepLink>(extraBufferCapacity = 1)
+    val chatNavigationEvents: SharedFlow<ChatDeepLink> = _chatNavigationEvents.asSharedFlow()
+
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         lifecycleScope.launch { seedDatabaseUseCase() }
         lifecycleScope.launch { ensureKeyPairUseCase.execute() }
         enableEdgeToEdge()
+        handleChatDeepLink(intent)
         setContent {
             BollwerkTheme {
-                MainScreen()
+                MainScreen(chatNavigationEvents = chatNavigationEvents)
             }
         }
     }
+
+    override fun onNewIntent(intent: Intent) {
+        super.onNewIntent(intent)
+        handleChatDeepLink(intent)
+    }
+
+    private fun handleChatDeepLink(intent: Intent?) {
+        val recipientId = intent?.getStringExtra(NotificationHelper.EXTRA_RECIPIENT_ID)
+        val recipientUsername = intent?.getStringExtra(NotificationHelper.EXTRA_RECIPIENT_USERNAME)
+        if (recipientId != null && recipientUsername != null) {
+            _chatNavigationEvents.tryEmit(ChatDeepLink(recipientId, recipientUsername))
+            // Clear extras to prevent re-navigation on config change
+            intent?.removeExtra(NotificationHelper.EXTRA_RECIPIENT_ID)
+            intent?.removeExtra(NotificationHelper.EXTRA_RECIPIENT_USERNAME)
+        }
+    }
 }
 
+data class ChatDeepLink(val recipientId: String, val recipientUsername: String)
+
 @Preview(showBackground = true)
 @Composable
 fun DefaultPreview() {

app/src/main/java/de/bollwerk/app/data/repository/MessageRepositoryImpl.kt

@@ -14,6 +14,7 @@ import de.bollwerk.app.domain.model.SettingsKey.StringKey
 import de.bollwerk.app.domain.model.SyncError
 import de.bollwerk.app.domain.repository.MessageRepository
 import de.bollwerk.app.domain.repository.SettingsRepository
+import de.bollwerk.app.notification.NotificationHelper
 import de.bollwerk.shared.model.SendMessageResponse
 import de.bollwerk.shared.model.UserListItemDto
 import io.ktor.client.HttpClient
@@ -57,6 +58,7 @@ internal class MessageRepositoryImpl @Inject constructor(
     private val webSocketClient: WebSocketClient,
     private val e2eeKeyManager: E2EEKeyManager,
     private val authEventBus: AuthEventBus,
+    private val notificationHelper: NotificationHelper,
     @ApplicationScope private val scope: CoroutineScope
 ) : MessageRepository {
 
@@ -85,6 +87,10 @@ internal class MessageRepositoryImpl @Inject constructor(
                                 isPending = false
                             )
                         )
+                        notificationHelper.showNewMessageNotification(
+                            senderId = msg.senderId,
+                            senderUsername = msg.senderUsername
+                        )
                     }
                     is WebSocketEvent.KeyUpdated -> {
                         publicKeyCache[event.userId] = event.publicKey

app/src/main/java/de/bollwerk/app/notification/NotificationHelper.kt

@@ -0,0 +1,119 @@
+package de.bollwerk.app.notification
+
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.app.PendingIntent
+import android.content.Context
+import android.content.Intent
+import android.media.AudioAttributes
+import android.media.RingtoneManager
+import androidx.core.app.NotificationCompat
+import androidx.core.app.NotificationManagerCompat
+import dagger.hilt.android.qualifiers.ApplicationContext
+import de.bollwerk.app.MainActivity
+import de.bollwerk.app.R
+import javax.inject.Inject
+import javax.inject.Singleton
+
+@Singleton
+internal class NotificationHelper @Inject constructor(
+    @ApplicationContext private val context: Context
+) {
+
+    @Volatile
+    private var activeChatPartnerId: String? = null
+
+    /// Erstellt den Notification Channel (ab API 26 erforderlich).
+    fun createNotificationChannel() {
+        val soundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION)
+        val audioAttributes = AudioAttributes.Builder()
+            .setContentType(AudioAttributes.CONTENT_TYPE_SONIFICATION)
+            .setUsage(AudioAttributes.USAGE_NOTIFICATION)
+            .build()
+
+        val channel = NotificationChannel(
+            CHANNEL_ID,
+            CHANNEL_NAME,
+            NotificationManager.IMPORTANCE_HIGH
+        ).apply {
+            description = "Benachrichtigungen für eingehende Chat-Nachrichten"
+            setSound(soundUri, audioAttributes)
+            enableVibration(true)
+        }
+
+        val manager = context.getSystemService(NotificationManager::class.java)
+        manager.createNotificationChannel(channel)
+    }
+
+    /// Setzt die aktuell sichtbare Chat-Konversation (unterdrückt Notifications für diesen Partner).
+    fun setActiveChat(partnerId: String?) {
+        activeChatPartnerId = partnerId
+    }
+
+    /// Zeigt eine Benachrichtigung für eine eingehende Nachricht an.
+    /// Gibt false zurück, wenn die Notification unterdrückt wurde (Chat ist aktiv).
+    fun showNewMessageNotification(
+        senderId: String,
+        senderUsername: String
+    ): Boolean {
+        if (senderId == activeChatPartnerId) return false
+
+        val intent = Intent(context, MainActivity::class.java).apply {
+            flags = Intent.FLAG_ACTIVITY_SINGLE_TOP or Intent.FLAG_ACTIVITY_CLEAR_TOP
+            putExtra(EXTRA_RECIPIENT_ID, senderId)
+            putExtra(EXTRA_RECIPIENT_USERNAME, senderUsername)
+        }
+
+        val pendingIntent = PendingIntent.getActivity(
+            context,
+            senderId.hashCode(),
+            intent,
+            PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE
+        )
+
+        val notification = NotificationCompat.Builder(context, CHANNEL_ID)
+            .setSmallIcon(R.drawable.ic_notification_message)
+            .setContentTitle("Neue Nachricht")
+            .setContentText("$senderUsername hat etwas geschrieben")
+            .setPriority(NotificationCompat.PRIORITY_HIGH)
+            .setAutoCancel(true)
+            .setContentIntent(pendingIntent)
+            .setGroup(GROUP_KEY)
+            .build()
+
+        val summaryNotification = NotificationCompat.Builder(context, CHANNEL_ID)
+            .setSmallIcon(R.drawable.ic_notification_message)
+            .setContentTitle("Neue Nachrichten")
+            .setContentText("Du hast neue Nachrichten")
+            .setGroup(GROUP_KEY)
+            .setGroupSummary(true)
+            .setAutoCancel(true)
+            .build()
+
+        val notificationManager = NotificationManagerCompat.from(context)
+        try {
+            notificationManager.notify(senderId.hashCode(), notification)
+            notificationManager.notify(SUMMARY_NOTIFICATION_ID, summaryNotification)
+        } catch (_: SecurityException) {
+            // Permission not granted – ignore silently
+            return false
+        }
+        return true
+    }
+
+    /// Entfernt Benachrichtigungen für einen bestimmten Absender (wenn der Chat geöffnet wird).
+    fun cancelNotificationForSender(senderId: String) {
+        val notificationManager = NotificationManagerCompat.from(context)
+        notificationManager.cancel(senderId.hashCode())
+    }
+
+    companion object {
+        const val CHANNEL_ID = "bollwerk_messages"
+        private const val CHANNEL_NAME = "Chat-Nachrichten"
+        private const val GROUP_KEY = "de.bollwerk.app.MESSAGES"
+        private const val SUMMARY_NOTIFICATION_ID = 0
+
+        const val EXTRA_RECIPIENT_ID = "notification_recipient_id"
+        const val EXTRA_RECIPIENT_USERNAME = "notification_recipient_username"
+    }
+}

app/src/main/java/de/bollwerk/app/ui/MainScreen.kt

@@ -35,6 +35,7 @@ import androidx.navigation.NavDestination.Companion.hasRoute
 import androidx.navigation.NavGraph.Companion.findStartDestination
 import androidx.navigation.compose.currentBackStackEntryAsState
 import androidx.navigation.compose.rememberNavController
+import de.bollwerk.app.ChatDeepLink
 import de.bollwerk.app.ui.inventory.InventoryPickerSheet
 import de.bollwerk.app.ui.inventory.InventoryPickerViewModel
 import de.bollwerk.app.ui.navigation.BollwerkNavGraph
@@ -43,10 +44,11 @@ import de.bollwerk.app.ui.navigation.TopLevelDestination
 import de.bollwerk.app.ui.update.UpdateBanner
 import de.bollwerk.app.ui.update.UpdateStatus
 import de.bollwerk.app.ui.update.UpdateViewModel
+import kotlinx.coroutines.flow.SharedFlow
 
 @OptIn(ExperimentalMaterial3Api::class)
 @Composable
-internal fun MainScreen() {
+internal fun MainScreen(chatNavigationEvents: SharedFlow<ChatDeepLink>) {
     val navController = rememberNavController()
     val navBackStackEntry by navController.currentBackStackEntryAsState()
     val currentDestination = navBackStackEntry?.destination
@@ -65,6 +67,19 @@ internal fun MainScreen() {
         }
     }
 
+    LaunchedEffect(Unit) {
+        chatNavigationEvents.collect { deepLink ->
+            navController.navigate(
+                Screen.Chat(
+                    recipientId = deepLink.recipientId,
+                    recipientUsername = deepLink.recipientUsername
+                )
+            ) {
+                launchSingleTop = true
+            }
+        }
+    }
+
     val inventoryPickerViewModel: InventoryPickerViewModel = hiltViewModel()
     val inventoryState by inventoryPickerViewModel.uiState.collectAsStateWithLifecycle()
     var isInventoryPickerVisible by remember { mutableStateOf(false) }

app/src/main/java/de/bollwerk/app/ui/messaging/ChatViewModel.kt

@@ -6,6 +6,7 @@ import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
 import de.bollwerk.app.data.db.entity.MessageEntity
 import de.bollwerk.app.domain.repository.MessageRepository
+import de.bollwerk.app.notification.NotificationHelper
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.update
@@ -23,7 +24,8 @@ internal data class ChatUiState(
 @HiltViewModel
 internal class ChatViewModel @Inject constructor(
     savedStateHandle: SavedStateHandle,
-    private val messageRepository: MessageRepository
+    private val messageRepository: MessageRepository,
+    private val notificationHelper: NotificationHelper
 ) : ViewModel() {
 
     private val recipientId: String = savedStateHandle.get<String>("recipientId") ?: ""
@@ -33,6 +35,8 @@ internal class ChatViewModel @Inject constructor(
     val uiState: StateFlow<ChatUiState> = _uiState
 
     init {
+        notificationHelper.setActiveChat(recipientId)
+        notificationHelper.cancelNotificationForSender(recipientId)
         viewModelScope.launch {
             val myId = messageRepository.getMyUserId() ?: ""
             _uiState.update { it.copy(myUserId = myId) }
@@ -44,6 +48,11 @@ internal class ChatViewModel @Inject constructor(
         }
     }
 
+    override fun onCleared() {
+        super.onCleared()
+        notificationHelper.setActiveChat(null)
+    }
+
     fun onInputChanged(text: String) {
         _uiState.update { it.copy(inputText = text) }
     }

app/src/main/res/drawable/ic_notification_message.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:fillColor="@android:color/white"
+        android:pathData="M20,2L4,2c-1.1,0 -1.99,0.9 -1.99,2L2,22l4,-4h14c1.1,0 2,-0.9 2,-2L22,4c0,-1.1 -0.9,-2 -2,-2zM6,9h12v2L6,11L6,9zM14,14L6,14v-2h8v2zM18,8L6,8L6,6h12v2z"/>
+</vector>

app/src/test/java/de/bollwerk/app/data/repository/MessageRepositoryImplTest.kt

@@ -5,9 +5,11 @@ import de.bollwerk.app.data.db.entity.MessageEntity
 import de.bollwerk.app.data.security.E2EEKeyManager
 import de.bollwerk.app.data.sync.WebSocketClient
 import de.bollwerk.app.data.sync.WebSocketEvent
+import de.bollwerk.app.domain.AuthEventBus
 import de.bollwerk.app.domain.model.SettingsKey
 import de.bollwerk.app.domain.model.SettingsKeys
 import de.bollwerk.app.domain.repository.SettingsRepository
+import de.bollwerk.app.notification.NotificationHelper
 import de.bollwerk.shared.model.MessageDto
 import de.bollwerk.shared.model.UserListItemDto
 import io.ktor.client.HttpClient
@@ -124,6 +126,8 @@ class MessageRepositoryImplTest {
         settingsRepository = settings,
         webSocketClient = wsClient,
         e2eeKeyManager = e2eeKeyManager,
+        authEventBus = AuthEventBus(),
+        notificationHelper = mockk(relaxed = true),
         scope = testScope
     )
 

app/src/test/java/de/bollwerk/app/data/sync/SyncServiceImplTest.kt

@@ -1,5 +1,6 @@
-package de.bollwerk.app.data.sync
+package de.bollwerk.app.data.sync
 
+import de.bollwerk.app.domain.AuthEventBus
 import de.bollwerk.app.domain.model.SettingsKey.StringKey
 import de.bollwerk.app.domain.model.SyncError
 import de.bollwerk.app.domain.repository.SettingsRepository
@@ -97,7 +98,7 @@ class SyncServiceImplTest {
             )
         }
         httpClient = createClient(engine)
-        syncService = SyncServiceImpl(httpClient, settingsRepository)
+        syncService = SyncServiceImpl(httpClient, settingsRepository, AuthEventBus())
 
         // When
         val result = syncService.downloadInventory()
@@ -115,7 +116,7 @@ class SyncServiceImplTest {
             respondError(HttpStatusCode.Unauthorized)
         }
         httpClient = createClient(engine)
-        syncService = SyncServiceImpl(httpClient, settingsRepository)
+        syncService = SyncServiceImpl(httpClient, settingsRepository, AuthEventBus())
 
         // When
         val result = syncService.downloadInventory()
@@ -133,7 +134,7 @@ class SyncServiceImplTest {
             respondError(HttpStatusCode.InternalServerError)
         }
         httpClient = createClient(engine)
-        syncService = SyncServiceImpl(httpClient, settingsRepository)
+        syncService = SyncServiceImpl(httpClient, settingsRepository, AuthEventBus())
 
         // When
         val result = syncService.downloadInventory()
@@ -150,7 +151,7 @@ class SyncServiceImplTest {
         setupSettings(serverUrl = null)
         val engine = MockEngine { respondError(HttpStatusCode.OK) }
         httpClient = createClient(engine)
-        syncService = SyncServiceImpl(httpClient, settingsRepository)
+        syncService = SyncServiceImpl(httpClient, settingsRepository, AuthEventBus())
 
         // When
         val result = syncService.downloadInventory()
@@ -166,7 +167,7 @@ class SyncServiceImplTest {
         setupSettings(serverUrl = "  ")
         val engine = MockEngine { respondError(HttpStatusCode.OK) }
         httpClient = createClient(engine)
-        syncService = SyncServiceImpl(httpClient, settingsRepository)
+        syncService = SyncServiceImpl(httpClient, settingsRepository, AuthEventBus())
 
         // When
         val result = syncService.downloadInventory()
@@ -182,7 +183,7 @@ class SyncServiceImplTest {
         setupSettings(accessToken = null)
         val engine = MockEngine { respondError(HttpStatusCode.OK) }
         httpClient = createClient(engine)
-        syncService = SyncServiceImpl(httpClient, settingsRepository)
+        syncService = SyncServiceImpl(httpClient, settingsRepository, AuthEventBus())
 
         // When
         val result = syncService.downloadInventory()
@@ -206,7 +207,7 @@ class SyncServiceImplTest {
             )
         }
         httpClient = createClient(engine)
-        syncService = SyncServiceImpl(httpClient, settingsRepository)
+        syncService = SyncServiceImpl(httpClient, settingsRepository, AuthEventBus())
 
         // When
         val result = syncService.downloadInventory(since = 1715000000L)
@@ -228,7 +229,7 @@ class SyncServiceImplTest {
             )
         }
         httpClient = createClient(engine)
-        syncService = SyncServiceImpl(httpClient, settingsRepository)
+        syncService = SyncServiceImpl(httpClient, settingsRepository, AuthEventBus())
 
         // When
         val result = syncService.downloadInventory(since = null)
@@ -258,7 +259,7 @@ class SyncServiceImplTest {
             )
         }
         httpClient = createClient(engine)
-        syncService = SyncServiceImpl(httpClient, settingsRepository)
+        syncService = SyncServiceImpl(httpClient, settingsRepository, AuthEventBus())
 
         // When
         val result = syncService.uploadInventory(testInventory)
@@ -276,7 +277,7 @@ class SyncServiceImplTest {
             respondError(HttpStatusCode.Unauthorized)
         }
         httpClient = createClient(engine)
-        syncService = SyncServiceImpl(httpClient, settingsRepository)
+        syncService = SyncServiceImpl(httpClient, settingsRepository, AuthEventBus())
 
         // When
         val result = syncService.uploadInventory(testInventory)
@@ -299,7 +300,7 @@ class SyncServiceImplTest {
             )
         }
         httpClient = createClient(engine)
-        syncService = SyncServiceImpl(httpClient, settingsRepository)
+        syncService = SyncServiceImpl(httpClient, settingsRepository, AuthEventBus())
 
         // When
         val result = syncService.uploadInventory(testInventory)

app/src/test/java/de/bollwerk/app/notification/NotificationHelperTest.kt

@@ -0,0 +1,63 @@
+package de.bollwerk.app.notification
+
+import android.app.NotificationManager
+import android.content.Context
+import io.mockk.every
+import io.mockk.mockk
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertNull
+import org.junit.Before
+import org.junit.Test
+
+class NotificationHelperTest {
+
+    private lateinit var context: Context
+    private lateinit var notificationManager: NotificationManager
+    private lateinit var notificationHelper: NotificationHelper
+
+    @Before
+    fun setup() {
+        context = mockk(relaxed = true)
+        notificationManager = mockk(relaxed = true)
+        every { context.getSystemService(NotificationManager::class.java) } returns notificationManager
+        every { context.packageName } returns "de.bollwerk.app"
+
+        notificationHelper = NotificationHelper(context)
+    }
+
+    @Test
+    fun test_showNewMessageNotification_activeChatMatchesSender_returnsFalse() {
+        // Given
+        notificationHelper.setActiveChat("user-123")
+
+        // When
+        val result = notificationHelper.showNewMessageNotification(
+            senderId = "user-123",
+            senderUsername = "Bob"
+        )
+
+        // Then
+        assertFalse(result)
+    }
+
+    @Test
+    fun test_setActiveChat_setsAndClears() {
+        // Given
+        notificationHelper.setActiveChat("user-123")
+
+        // When – message from same user is suppressed
+        val suppressed = notificationHelper.showNewMessageNotification(
+            senderId = "user-123",
+            senderUsername = "Bob"
+        )
+
+        // Then
+        assertFalse(suppressed)
+
+        // When – clear active chat
+        notificationHelper.setActiveChat(null)
+
+        // Then – message from same user is no longer suppressed at the guard
+        // (actual notification display needs Android runtime, tested via instrumentation)
+    }
+}

app/src/test/java/de/bollwerk/app/ui/messaging/ChatViewModelTest.kt

@@ -3,7 +3,9 @@ package de.bollwerk.app.ui.messaging
 import androidx.lifecycle.SavedStateHandle
 import de.bollwerk.app.data.db.entity.MessageEntity
 import de.bollwerk.app.domain.repository.MessageRepository
+import de.bollwerk.app.notification.NotificationHelper
 import de.bollwerk.shared.model.UserListItemDto
+import io.mockk.mockk
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.Flow
@@ -58,7 +60,7 @@ class ChatViewModelTest {
         repo: MessageRepository = FakeChatMessageRepository()
     ): ChatViewModel {
         val savedStateHandle = SavedStateHandle(mapOf("recipientId" to recipientId, "recipientUsername" to recipientUsername))
-        return ChatViewModel(savedStateHandle = savedStateHandle, messageRepository = repo)
+        return ChatViewModel(savedStateHandle = savedStateHandle, messageRepository = repo, notificationHelper = mockk(relaxed = true))
     }
 
     @Test