e-ntfy-android/app/src/main/java/io/heckel/ntfy/msg/SubscriberService.kt

package io.heckel.ntfy.msg

import android.app.*
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.os.Build
import android.os.IBinder
import android.os.PowerManager
import android.os.SystemClock
import android.util.Log
import androidx.core.app.NotificationCompat
import io.heckel.ntfy.R
import io.heckel.ntfy.app.Application
import io.heckel.ntfy.data.ConnectionState
import io.heckel.ntfy.data.Subscription
import io.heckel.ntfy.data.topicUrl
import io.heckel.ntfy.ui.MainActivity
import kotlinx.coroutines.*
import okhttp3.Call
import java.util.concurrent.ConcurrentHashMap
import java.util.concurrent.atomic.AtomicBoolean

/**
 *
 * Largely modeled after this fantastic resource:
 * - https://robertohuertas.com/2019/06/29/android_foreground_services/
 * - https://github.com/robertohuertasm/endless-service/blob/master/app/src/main/java/com/robertohuertas/endless/EndlessService.kt
 */
class SubscriberService : Service() {
    private var wakeLock: PowerManager.WakeLock? = null
    private var isServiceStarted = false
    private val repository by lazy { (application as Application).repository }
    private val jobs = ConcurrentHashMap<Long, Job>() // Subscription ID -> Job
    private val calls = ConcurrentHashMap<Long, Call>() // Subscription ID -> Cal
    private val api = ApiService()
    private val notifier = NotificationService(this)
    private var notificationManager: NotificationManager? = null
    private var notification: Notification? = null

    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
        Log.d(TAG, "onStartCommand executed with startId: $startId")
        if (intent != null) {
            val action = intent.action
            Log.d(TAG, "using an intent with action $action")
            when (action) {
                Actions.START.name -> startService()
                Actions.STOP.name -> stopService()
                else -> Log.e(TAG, "This should never happen. No action in the received intent")
            }
        } else {
            Log.d(TAG, "with a null intent. It has been probably restarted by the system.")
        }
        return START_STICKY // restart if system kills the service
    }

    override fun onCreate() {
        super.onCreate()
        Log.d(TAG, "Subscriber service has been created")

        val title = getString(R.string.channel_subscriber_notification_title)
        val text = getString(R.string.channel_subscriber_notification_text)
        notificationManager = createNotificationChannel()
        notification = createNotification(title, text)

        startForeground(NOTIFICATION_SERVICE_ID, notification)
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.d(TAG, "Subscriber service has been destroyed")
    }

    private fun startService() {
        if (isServiceStarted) {
            launchAndCancelJobs()
            return
        }
        Log.d(TAG, "Starting the foreground service task")
        isServiceStarted = true
        saveServiceState(this, ServiceState.STARTED)
        wakeLock = (getSystemService(Context.POWER_SERVICE) as PowerManager).run {
            newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, WAKE_LOCK_TAG).apply {
                acquire()
            }
        }
        launchAndCancelJobs()
    }

    private fun stopService() {
        Log.d(TAG, "Stopping the foreground service")

        // Cancelling all remaining jobs and open HTTP calls
        jobs.values.forEach { job -> job.cancel() }
        calls.values.forEach { call -> call.cancel() }
        jobs.clear()
        calls.clear()

        // Releasing wake-lock and stopping ourselves
        try {
            wakeLock?.let {
                if (it.isHeld) {
                    it.release()
                }
            }
            stopForeground(true)
            stopSelf()
        } catch (e: Exception) {
            Log.d(TAG, "Service stopped without being started: ${e.message}")
        }

        isServiceStarted = false
        saveServiceState(this, ServiceState.STOPPED)
    }

    private fun launchAndCancelJobs() =
        GlobalScope.launch(Dispatchers.IO) {
            val subscriptions = repository.getSubscriptions().filter { s -> s.instant }
            val subscriptionIds = subscriptions.map { it.id }
            Log.d(TAG, "Refreshing subscriptions")
            Log.d(TAG, "- Subscriptions: $subscriptions")
            Log.d(TAG, "- Jobs: $jobs")
            Log.d(TAG, "- HTTP calls: $calls")
            subscriptions.forEach { subscription ->
                if (!jobs.containsKey(subscription.id)) {
                    jobs[subscription.id] = launchJob(this, subscription)
                }
            }
            jobs.keys().toList().forEach { subscriptionId ->
                if (!subscriptionIds.contains(subscriptionId)) {
                    cancelJob(subscriptionId)
                }
            }
            if (jobs.size > 0) {
                synchronized(this) {
                    val title = getString(R.string.channel_subscriber_notification_title)
                    val text = if (jobs.size == 1) {
                        getString(R.string.channel_subscriber_notification_text_one)
                    } else {
                        getString(R.string.channel_subscriber_notification_text_more, jobs.size)
                    }
                    notification = createNotification(title, text)
                    notificationManager?.notify(NOTIFICATION_SERVICE_ID, notification)
                }
            }
        }

    private fun cancelJob(subscriptionId: Long?) {
        Log.d(TAG, "Cancelling job for $subscriptionId")
        val job = jobs.remove(subscriptionId)
        val call = calls.remove(subscriptionId)
        job?.cancel()
        call?.cancel()
    }

    private fun launchJob(scope: CoroutineScope, subscription: Subscription): Job =
        scope.launch(Dispatchers.IO) {
            val url = topicUrl(subscription.baseUrl, subscription.topic)
            Log.d(TAG, "[$url] Starting connection job")

            // Retry-loop: if the connection fails, we retry unless the job or service is cancelled/stopped
            var since = 0L
            var retryMillis = 0L
            while (isActive && isServiceStarted) {
                Log.d(TAG, "[$url] (Re-)starting subscription for $subscription")
                val startTime = System.currentTimeMillis()
                val notify = { n: io.heckel.ntfy.data.Notification ->
                    since = n.timestamp
                    onNotificationReceived(scope, subscription, n)
                }
                val failed = AtomicBoolean(false)
                val fail = { e: Exception ->
                    failed.set(true)
                    repository.updateStateIfChanged(subscription.id, ConnectionState.RECONNECTING)
                }

                // Call /json subscribe endpoint and loop until the call fails, is canceled,
                // or the job or service are cancelled/stopped
                try {
                    val call = api.subscribe(subscription.id, subscription.baseUrl, subscription.topic, since, notify, fail)
                    calls[subscription.id] = call
                    while (!failed.get() && !call.isCanceled() && isActive && isServiceStarted) {
                        repository.updateStateIfChanged(subscription.id, ConnectionState.CONNECTED)
                        Log.d(TAG, "[$url] Connection is active (failed=$failed, callCanceled=${call.isCanceled()}, jobActive=$isActive, serviceStarted=$isServiceStarted")
                        delay(CONNECTION_LOOP_DELAY_MILLIS) // Resumes immediately if job is cancelled
                    }
                } catch (e: Exception) {
                    Log.e(TAG, "[$url] Connection failed: ${e.message}", e)
                    repository.updateStateIfChanged(subscription.id, ConnectionState.RECONNECTING)
                }

                // If we're not cancelled yet, wait little before retrying (incremental back-off)
                if (isActive && isServiceStarted) {
                    retryMillis = nextRetryMillis(retryMillis, startTime)
                    Log.d(TAG, "Connection failed, retrying connection in ${retryMillis/1000}s ...")
                    delay(retryMillis)
                }
            }
            Log.d(TAG, "[$url] Connection job SHUT DOWN")
            repository.updateStateIfChanged(subscription.id, ConnectionState.NOT_APPLICABLE)
        }

    private fun onNotificationReceived(scope: CoroutineScope, subscription: Subscription, n: io.heckel.ntfy.data.Notification) {
        val url = topicUrl(subscription.baseUrl, subscription.topic)
        Log.d(TAG, "[$url] Received notification: $n")
        scope.launch(Dispatchers.IO) {
            val added = repository.addNotification(n)
            if (added) {
                Log.d(TAG, "[$url] Showing notification: $n")
                notifier.send(subscription, n.message)
            }
        }
    }

    private fun nextRetryMillis(retryMillis: Long, startTime: Long): Long {
        val connectionDurationMillis = System.currentTimeMillis() - startTime
        if (connectionDurationMillis > RETRY_RESET_AFTER_MILLIS) {
            return RETRY_STEP_MILLIS
        } else if (retryMillis + RETRY_STEP_MILLIS >= RETRY_MAX_MILLIS) {
            return RETRY_MAX_MILLIS
        }
        return retryMillis + RETRY_STEP_MILLIS
    }

    private fun createNotificationChannel(): NotificationManager? {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            val notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
            val channelName = getString(R.string.channel_subscriber_service_name) // Show's up in UI
            val channel = NotificationChannel(NOTIFICATION_CHANNEL_ID, channelName, NotificationManager.IMPORTANCE_LOW).let {
                it.setShowBadge(false) // Don't show long-press badge
                it
            }
            notificationManager.createNotificationChannel(channel)
            return notificationManager
        }
        return null
    }

    private fun createNotification(title: String, text: String): Notification {
        val pendingIntent: PendingIntent = Intent(this, MainActivity::class.java).let { notificationIntent ->
            PendingIntent.getActivity(this, 0, notificationIntent, 0)
        }
        return NotificationCompat.Builder(this, NOTIFICATION_CHANNEL_ID)
            .setSmallIcon(R.drawable.ic_notification_instant)
            .setContentTitle(title)
            .setContentText(text)
            .setContentIntent(pendingIntent)
            .setSound(null)
            .setShowWhen(false) // Don't show date/time
            .build()
    }

    override fun onBind(intent: Intent): IBinder? {
        return null // We don't provide binding, so return null
    }

    /* This re-schedules the task when the "Clear recent apps" button is pressed */
    override fun onTaskRemoved(rootIntent: Intent) {
        val restartServiceIntent = Intent(applicationContext, SubscriberService::class.java).also {
            it.setPackage(packageName)
        };
        val restartServicePendingIntent: PendingIntent = PendingIntent.getService(this, 1, restartServiceIntent, PendingIntent.FLAG_ONE_SHOT);
        applicationContext.getSystemService(Context.ALARM_SERVICE);
        val alarmService: AlarmManager = applicationContext.getSystemService(Context.ALARM_SERVICE) as AlarmManager;
        alarmService.set(AlarmManager.ELAPSED_REALTIME, SystemClock.elapsedRealtime() + 1000, restartServicePendingIntent);
    }

    /* This re-starts the service on reboot; see manifest */
    class StartReceiver : BroadcastReceiver() {
        override fun onReceive(context: Context, intent: Intent) {
            if (intent.action == Intent.ACTION_BOOT_COMPLETED && readServiceState(context) == ServiceState.STARTED) {
                Intent(context, SubscriberService::class.java).also {
                    it.action = Actions.START.name
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                        Log.d(TAG, "Starting subscriber service in >=26 Mode from a BroadcastReceiver")
                        context.startForegroundService(it)
                        return
                    }
                    Log.d(TAG, "Starting subscriber service in < 26 Mode from a BroadcastReceiver")
                    context.startService(it)
                }
            }
        }
    }

    enum class Actions {
        START,
        STOP
    }

    enum class ServiceState {
        STARTED,
        STOPPED,
    }

    companion object {
        private const val TAG = "NtfySubscriberService"
        private const val WAKE_LOCK_TAG = "SubscriberService:lock"
        private const val NOTIFICATION_CHANNEL_ID = "ntfy-subscriber"
        private const val NOTIFICATION_SERVICE_ID = 2586
        private const val SHARED_PREFS_ID = "SubscriberService"
        private const val SHARED_PREFS_SERVICE_STATE = "ServiceState"
        private const val CONNECTION_LOOP_DELAY_MILLIS = 30_000L
        private const val RETRY_STEP_MILLIS = 5_000L
        private const val RETRY_MAX_MILLIS = 60_000L
        private const val RETRY_RESET_AFTER_MILLIS = 60_000L // Must be larger than CONNECTION_LOOP_DELAY_MILLIS

        fun saveServiceState(context: Context, state: ServiceState) {
            val sharedPrefs = context.getSharedPreferences(SHARED_PREFS_ID, Context.MODE_PRIVATE)
            sharedPrefs.edit()
                .putString(SHARED_PREFS_SERVICE_STATE, state.name)
                .apply()
        }

        fun readServiceState(context: Context): ServiceState {
            val sharedPrefs = context.getSharedPreferences(SHARED_PREFS_ID, Context.MODE_PRIVATE)
            val value = sharedPrefs.getString(SHARED_PREFS_SERVICE_STATE, ServiceState.STOPPED.name)
            return ServiceState.valueOf(value!!)
        }
    }
}