/*
 * Copyright 2019 Mauricio Colli <mauriciocolli@outlook.com>
 * FeedLoadService.kt is part of NewPipe
 *
 * License: GPL-3.0+
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

package org.schabi.newpipe.local.feed.service

import android.app.PendingIntent
import android.app.Service
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.content.IntentFilter
import android.os.Build
import android.os.IBinder
import android.util.Log
import androidx.core.app.NotificationCompat
import androidx.core.app.NotificationManagerCompat
import androidx.core.app.ServiceCompat
import androidx.preference.PreferenceManager
import io.reactivex.rxjava3.android.schedulers.AndroidSchedulers
import io.reactivex.rxjava3.core.Flowable
import io.reactivex.rxjava3.core.Notification
import io.reactivex.rxjava3.core.Single
import io.reactivex.rxjava3.disposables.CompositeDisposable
import io.reactivex.rxjava3.functions.Consumer
import io.reactivex.rxjava3.functions.Function
import io.reactivex.rxjava3.processors.PublishProcessor
import io.reactivex.rxjava3.schedulers.Schedulers
import org.reactivestreams.Subscriber
import org.reactivestreams.Subscription
import org.schabi.newpipe.MainActivity.DEBUG
import org.schabi.newpipe.R
import org.schabi.newpipe.database.feed.model.FeedGroupEntity
import org.schabi.newpipe.extractor.ListInfo
import org.schabi.newpipe.extractor.exceptions.ReCaptchaException
import org.schabi.newpipe.extractor.stream.StreamInfoItem
import org.schabi.newpipe.local.feed.FeedDatabaseManager
import org.schabi.newpipe.local.feed.service.FeedEventManager.Event.ErrorResultEvent
import org.schabi.newpipe.local.feed.service.FeedEventManager.Event.ProgressEvent
import org.schabi.newpipe.local.feed.service.FeedEventManager.Event.SuccessResultEvent
import org.schabi.newpipe.local.feed.service.FeedEventManager.postEvent
import org.schabi.newpipe.local.subscription.SubscriptionManager
import org.schabi.newpipe.util.ExceptionUtils
import org.schabi.newpipe.util.ExtractorHelper
import java.io.IOException
import java.time.OffsetDateTime
import java.time.ZoneOffset
import java.util.concurrent.TimeUnit
import java.util.concurrent.atomic.AtomicBoolean
import java.util.concurrent.atomic.AtomicInteger

class FeedLoadService : Service() {
    companion object {
        private val TAG = FeedLoadService::class.java.simpleName
        private const val NOTIFICATION_ID = 7293450
        private const val ACTION_CANCEL = "org.schabi.newpipe.local.feed.service.FeedLoadService.CANCEL"

        /**
         * How often the notification will be updated.
         */
        private const val NOTIFICATION_SAMPLING_PERIOD = 1500

        /**
         * How many extractions will be running in parallel.
         */
        private const val PARALLEL_EXTRACTIONS = 6

        /**
         * Number of items to buffer to mass-insert in the database.
         */
        private const val BUFFER_COUNT_BEFORE_INSERT = 20

        const val EXTRA_GROUP_ID: String = "FeedLoadService.EXTRA_GROUP_ID"
    }

    private var loadingSubscription: Subscription? = null
    private lateinit var subscriptionManager: SubscriptionManager

    private lateinit var feedDatabaseManager: FeedDatabaseManager
    private lateinit var feedResultsHolder: ResultsHolder

    private var disposables = CompositeDisposable()
    private var notificationUpdater = PublishProcessor.create<String>()

    // /////////////////////////////////////////////////////////////////////////
    // Lifecycle
    // /////////////////////////////////////////////////////////////////////////

    override fun onCreate() {
        super.onCreate()
        subscriptionManager = SubscriptionManager(this)
        feedDatabaseManager = FeedDatabaseManager(this)
    }

    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
        if (DEBUG) {
            Log.d(
                TAG,
                "onStartCommand() called with: intent = [" + intent + "]," +
                    " flags = [" + flags + "], startId = [" + startId + "]"
            )
        }

        if (intent == null || loadingSubscription != null) {
            return START_NOT_STICKY
        }

        setupNotification()
        setupBroadcastReceiver()
        val defaultSharedPreferences = PreferenceManager.getDefaultSharedPreferences(this)

        val groupId = intent.getLongExtra(EXTRA_GROUP_ID, FeedGroupEntity.GROUP_ALL_ID)
        val useFeedExtractor = defaultSharedPreferences
            .getBoolean(getString(R.string.feed_use_dedicated_fetch_method_key), false)

        val thresholdOutdatedSecondsString = defaultSharedPreferences
            .getString(getString(R.string.feed_update_threshold_key), getString(R.string.feed_update_threshold_default_value))
        val thresholdOutdatedSeconds = thresholdOutdatedSecondsString!!.toInt()

        startLoading(groupId, useFeedExtractor, thresholdOutdatedSeconds)

        return START_NOT_STICKY
    }

    private fun disposeAll() {
        unregisterReceiver(broadcastReceiver)

        loadingSubscription?.cancel()
        loadingSubscription = null

        disposables.dispose()
    }

    private fun stopService() {
        disposeAll()
        ServiceCompat.stopForeground(this, ServiceCompat.STOP_FOREGROUND_REMOVE)
        notificationManager.cancel(NOTIFICATION_ID)
        stopSelf()
    }

    override fun onBind(intent: Intent): IBinder? {
        return null
    }

    // /////////////////////////////////////////////////////////////////////////
    // Loading & Handling
    // /////////////////////////////////////////////////////////////////////////

    private class RequestException(val subscriptionId: Long, message: String, cause: Throwable) : Exception(message, cause) {
        companion object {
            fun wrapList(subscriptionId: Long, info: ListInfo<StreamInfoItem>): List<Throwable> {
                val toReturn = ArrayList<Throwable>(info.errors.size)
                info.errors.mapTo(toReturn) {
                    RequestException(subscriptionId, info.serviceId.toString() + ":" + info.url, it)
                }
                return toReturn
            }
        }
    }

    private fun startLoading(groupId: Long = FeedGroupEntity.GROUP_ALL_ID, useFeedExtractor: Boolean, thresholdOutdatedSeconds: Int) {
        feedResultsHolder = ResultsHolder()

        val outdatedThreshold = OffsetDateTime.now(ZoneOffset.UTC).minusSeconds(thresholdOutdatedSeconds.toLong())

        val subscriptions = when (groupId) {
            FeedGroupEntity.GROUP_ALL_ID -> feedDatabaseManager.outdatedSubscriptions(outdatedThreshold)
            else -> feedDatabaseManager.outdatedSubscriptionsForGroup(groupId, outdatedThreshold)
        }

        subscriptions
            .take(1)

            .doOnNext {
                currentProgress.set(0)
                maxProgress.set(it.size)
            }
            .filter { it.isNotEmpty() }

            .observeOn(AndroidSchedulers.mainThread())
            .doOnNext {
                startForeground(NOTIFICATION_ID, notificationBuilder.build())
                updateNotificationProgress(null)
                broadcastProgress()
            }

            .observeOn(Schedulers.io())
            .flatMap { Flowable.fromIterable(it) }
            .takeWhile { !cancelSignal.get() }

            .parallel(PARALLEL_EXTRACTIONS, PARALLEL_EXTRACTIONS * 2)
            .runOn(Schedulers.io(), PARALLEL_EXTRACTIONS * 2)
            .filter { !cancelSignal.get() }

            .map { subscriptionEntity ->
                try {
                    val listInfo = if (useFeedExtractor) {
                        ExtractorHelper
                            .getFeedInfoFallbackToChannelInfo(subscriptionEntity.serviceId, subscriptionEntity.url)
                            .blockingGet()
                    } else {
                        ExtractorHelper
                            .getChannelInfo(subscriptionEntity.serviceId, subscriptionEntity.url, true)
                            .blockingGet()
                    } as ListInfo<StreamInfoItem>

                    return@map Notification.createOnNext(Pair(subscriptionEntity.uid, listInfo))
                } catch (e: Throwable) {
                    val request = "${subscriptionEntity.serviceId}:${subscriptionEntity.url}"
                    val wrapper = RequestException(subscriptionEntity.uid, request, e)
                    return@map Notification.createOnError<Pair<Long, ListInfo<StreamInfoItem>>>(wrapper)
                }
            }
            .sequential()

            .observeOn(AndroidSchedulers.mainThread())
            .doOnNext(errorHandlingConsumer)

            .observeOn(AndroidSchedulers.mainThread())
            .doOnNext(notificationsConsumer)

            .observeOn(Schedulers.io())
            .buffer(BUFFER_COUNT_BEFORE_INSERT)
            .doOnNext(databaseConsumer)

            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(resultSubscriber)
    }

    private fun broadcastProgress() {
        postEvent(ProgressEvent(currentProgress.get(), maxProgress.get()))
    }

    private val resultSubscriber
        get() = object : Subscriber<List<Notification<Pair<Long, ListInfo<StreamInfoItem>>>>> {

            override fun onSubscribe(s: Subscription) {
                loadingSubscription = s
                s.request(java.lang.Long.MAX_VALUE)
            }

            override fun onNext(notification: List<Notification<Pair<Long, ListInfo<StreamInfoItem>>>>) {
                if (DEBUG) Log.v(TAG, "onNext() → $notification")
            }

            override fun onError(error: Throwable) {
                handleError(error)
            }

            override fun onComplete() {
                if (maxProgress.get() == 0) {
                    postEvent(FeedEventManager.Event.IdleEvent)
                    stopService()

                    return
                }

                currentProgress.set(-1)
                maxProgress.set(-1)

                notificationUpdater.onNext(getString(R.string.feed_processing_message))
                postEvent(ProgressEvent(R.string.feed_processing_message))

                disposables.add(
                    Single
                        .fromCallable {
                            feedResultsHolder.ready()

                            postEvent(ProgressEvent(R.string.feed_processing_message))
                            feedDatabaseManager.removeOrphansOrOlderStreams()

                            postEvent(SuccessResultEvent(feedResultsHolder.itemsErrors))
                            true
                        }
                        .subscribeOn(Schedulers.io())
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribe { _, throwable ->
                            if (throwable != null) {
                                Log.e(TAG, "Error while storing result", throwable)
                                handleError(throwable)
                                return@subscribe
                            }
                            stopService()
                        }
                )
            }
        }

    private val databaseConsumer: Consumer<List<Notification<Pair<Long, ListInfo<StreamInfoItem>>>>>
        get() = Consumer {
            feedDatabaseManager.database().runInTransaction {
                for (notification in it) {

                    if (notification.isOnNext) {
                        val subscriptionId = notification.value!!.first
                        val info = notification.value!!.second

                        feedDatabaseManager.upsertAll(subscriptionId, info.relatedItems)
                        subscriptionManager.updateFromInfo(subscriptionId, info)

                        if (info.errors.isNotEmpty()) {
                            feedResultsHolder.addErrors(RequestException.wrapList(subscriptionId, info))
                            feedDatabaseManager.markAsOutdated(subscriptionId)
                        }
                    } else if (notification.isOnError) {
                        val error = notification.error!!
                        feedResultsHolder.addError(error)

                        if (error is RequestException) {
                            feedDatabaseManager.markAsOutdated(error.subscriptionId)
                        }
                    }
                }
            }
        }

    private val errorHandlingConsumer: Consumer<Notification<Pair<Long, ListInfo<StreamInfoItem>>>>
        get() = Consumer {
            if (it.isOnError) {
                var error = it.error!!
                if (error is RequestException) error = error.cause!!
                val cause = error.cause

                when {
                    error is ReCaptchaException -> throw error
                    cause is ReCaptchaException -> throw cause

                    error is IOException -> throw error
                    cause is IOException -> throw cause
                    ExceptionUtils.isNetworkRelated(error) -> throw IOException(error)
                }
            }
        }

    private val notificationsConsumer: Consumer<Notification<Pair<Long, ListInfo<StreamInfoItem>>>>
        get() = Consumer { onItemCompleted(it.value?.second?.name) }

    private fun onItemCompleted(updateDescription: String?) {
        currentProgress.incrementAndGet()
        notificationUpdater.onNext(updateDescription ?: "")

        broadcastProgress()
    }

    // /////////////////////////////////////////////////////////////////////////
    // Notification
    // /////////////////////////////////////////////////////////////////////////

    private lateinit var notificationManager: NotificationManagerCompat
    private lateinit var notificationBuilder: NotificationCompat.Builder

    private var currentProgress = AtomicInteger(-1)
    private var maxProgress = AtomicInteger(-1)

    private fun createNotification(): NotificationCompat.Builder {
        val cancelActionIntent = PendingIntent.getBroadcast(
            this,
            NOTIFICATION_ID, Intent(ACTION_CANCEL), 0
        )

        return NotificationCompat.Builder(this, getString(R.string.notification_channel_id))
            .setOngoing(true)
            .setProgress(-1, -1, true)
            .setSmallIcon(R.drawable.ic_newpipe_triangle_white)
            .setVisibility(NotificationCompat.VISIBILITY_PUBLIC)
            .addAction(0, getString(R.string.cancel), cancelActionIntent)
            .setContentTitle(getString(R.string.feed_notification_loading))
    }

    private fun setupNotification() {
        notificationManager = NotificationManagerCompat.from(this)
        notificationBuilder = createNotification()

        val throttleAfterFirstEmission = Function { flow: Flowable<String> ->
            flow.take(1).concatWith(flow.skip(1).throttleLatest(NOTIFICATION_SAMPLING_PERIOD.toLong(), TimeUnit.MILLISECONDS))
        }

        disposables.add(
            notificationUpdater
                .publish(throttleAfterFirstEmission)
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(this::updateNotificationProgress)
        )
    }

    private fun updateNotificationProgress(updateDescription: String?) {
        notificationBuilder.setProgress(maxProgress.get(), currentProgress.get(), maxProgress.get() == -1)

        if (maxProgress.get() == -1) {
            if (Build.VERSION.SDK_INT < Build.VERSION_CODES.N) notificationBuilder.setContentInfo(null)
            if (!updateDescription.isNullOrEmpty()) notificationBuilder.setContentText(updateDescription)
            notificationBuilder.setContentText(updateDescription)
        } else {
            val progressText = this.currentProgress.toString() + "/" + maxProgress

            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
                if (!updateDescription.isNullOrEmpty()) notificationBuilder.setContentText("$updateDescription  ($progressText)")
            } else {
                notificationBuilder.setContentInfo(progressText)
                if (!updateDescription.isNullOrEmpty()) notificationBuilder.setContentText(updateDescription)
            }
        }

        notificationManager.notify(NOTIFICATION_ID, notificationBuilder.build())
    }

    // /////////////////////////////////////////////////////////////////////////
    // Notification Actions
    // /////////////////////////////////////////////////////////////////////////

    private lateinit var broadcastReceiver: BroadcastReceiver
    private val cancelSignal = AtomicBoolean()

    private fun setupBroadcastReceiver() {
        broadcastReceiver = object : BroadcastReceiver() {
            override fun onReceive(context: Context?, intent: Intent?) {
                if (intent?.action == ACTION_CANCEL) {
                    cancelSignal.set(true)
                }
            }
        }
        registerReceiver(broadcastReceiver, IntentFilter(ACTION_CANCEL))
    }

    // /////////////////////////////////////////////////////////////////////////
    // Error handling
    // /////////////////////////////////////////////////////////////////////////

    private fun handleError(error: Throwable) {
        postEvent(ErrorResultEvent(error))
        stopService()
    }

    // /////////////////////////////////////////////////////////////////////////
    // Results Holder
    // /////////////////////////////////////////////////////////////////////////

    class ResultsHolder {
        /**
         * List of errors that may have happen during loading.
         */
        internal lateinit var itemsErrors: List<Throwable>

        private val itemsErrorsHolder: MutableList<Throwable> = ArrayList()

        fun addError(error: Throwable) {
            itemsErrorsHolder.add(error)
        }

        fun addErrors(errors: List<Throwable>) {
            itemsErrorsHolder.addAll(errors)
        }

        fun ready() {
            itemsErrors = itemsErrorsHolder.toList()
        }
    }
}