Firebase Cloud Messaging and Push Notifications

dependencies {
    implementation(platform("com.google.firebase:firebase-bom:<latest>"))
    implementation("com.google.firebase:firebase-messaging")
}

<uses-permission android:name="android.permission.POST_NOTIFICATIONS" />

<application>
    <service
        android:name=".push.AppMessagingService"
        android:exported="false">
        <intent-filter>
            <action android:name="com.google.firebase.MESSAGING_EVENT" />
        </intent-filter>
    </service>
    <meta-data
        android:name="com.google.firebase.messaging.default_notification_channel_id"
        android:value="general" />
</application>

@Composable
fun rememberNotificationPermissionRequester(onResult: (Boolean) -> Unit): () -> Unit {
    val launcher = rememberLauncherForActivityResult(ActivityResultContracts.RequestPermission(), onResult)
    return remember {
        {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
                launcher.launch(Manifest.permission.POST_NOTIFICATIONS)
            } else onResult(true)        // granted by default below Android 13 (user can still disable)
        }
    }
}

fun createNotificationChannels(context: Context) {
    val manager = context.getSystemService(NotificationManager::class.java)
    manager.createNotificationChannels(listOf(
        NotificationChannel("orders", "Order updates", NotificationManager.IMPORTANCE_HIGH)
            .apply { description = "Shipping and delivery status" },
        NotificationChannel("general", "General", NotificationManager.IMPORTANCE_DEFAULT),
        NotificationChannel("promotions", "Offers", NotificationManager.IMPORTANCE_LOW),
    ))
}

class AppMessagingService : FirebaseMessagingService() {

    override fun onNewToken(token: String) {
        // Tokens can change (reinstall, data cleared). Send to backend via WorkManager for reliability.
        TokenUploadWorker.enqueue(applicationContext, token)
    }

    override fun onMessageReceived(message: RemoteMessage) {
        // Data messages arrive here in foreground and background.
        // Notification messages arrive here only when the app is in the foreground.
        val data = message.data
        when (data["type"]) {
            "order_update" -> showOrderNotification(
                orderId = data["orderId"] ?: return,
                title = data["title"] ?: "Order update",
                body = data["body"].orEmpty(),
            )
            "sync" -> SyncScheduler(WorkManager.getInstance(this)).requestSync()   // silent refresh
        }
    }

    private fun showOrderNotification(orderId: String, title: String, body: String) {
        val intent = Intent(Intent.ACTION_VIEW, "https://yunoktech.com/orders/$orderId".toUri(), this, MainActivity::class.java)
        val pending = PendingIntent.getActivity(this, orderId.hashCode(), intent,
            PendingIntent.FLAG_IMMUTABLE or PendingIntent.FLAG_UPDATE_CURRENT)
        val notification = NotificationCompat.Builder(this, "orders")
            .setSmallIcon(R.drawable.ic_stat_notify)
            .setContentTitle(title)
            .setContentText(body)
            .setAutoCancel(true)
            .setContentIntent(pending)
            .build()
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.POST_NOTIFICATIONS) == PackageManager.PERMISSION_GRANTED ||
            Build.VERSION.SDK_INT < Build.VERSION_CODES.TIRAMISU) {
            NotificationManagerCompat.from(this).notify(orderId.hashCode(), notification)
        }
    }
}

{
  "message": {
    "token": "DEVICE_REGISTRATION_TOKEN",
    "data": {
      "type": "order_update",
      "orderId": "A1042",
      "title": "Out for delivery",
      "body": "Your order arrives today by 6 PM"
    },
    "android": { "priority": "high" }
  }
}