LibreTube/app/src/main/java/com/github/libretube/services/BackgroundMode.kt

package com.github.libretube.services

import android.app.Notification
import android.app.NotificationChannel
import android.app.NotificationManager
import android.app.Service
import android.content.Intent
import android.os.Build
import android.os.Handler
import android.os.IBinder
import android.os.Looper
import com.fasterxml.jackson.databind.ObjectMapper
import com.github.libretube.BACKGROUND_CHANNEL_ID
import com.github.libretube.PLAYER_NOTIFICATION_ID
import com.github.libretube.R
import com.github.libretube.obj.Segment
import com.github.libretube.obj.Segments
import com.github.libretube.obj.Streams
import com.github.libretube.preferences.PreferenceHelper
import com.github.libretube.preferences.PreferenceKeys
import com.github.libretube.util.NowPlayingNotification
import com.github.libretube.util.PlayerHelper
import com.github.libretube.util.RetrofitInstance
import com.github.libretube.util.toID
import com.google.android.exoplayer2.C
import com.google.android.exoplayer2.ExoPlayer
import com.google.android.exoplayer2.MediaItem
import com.google.android.exoplayer2.Player
import com.google.android.exoplayer2.audio.AudioAttributes
import com.google.android.exoplayer2.ext.mediasession.MediaSessionConnector
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.launch
import kotlinx.coroutines.runBlocking

/**
 * Loads the selected videos audio in background mode with a notification area.
 */
class BackgroundMode : Service() {
    /**
     * VideoId of the video
     */
    private lateinit var videoId: String

    /**
     * The response that gets when called the Api.
     */
    private var response: Streams? = null

    /**
     * The [ExoPlayer] player. Followed tutorial [here](https://developer.android.com/codelabs/exoplayer-intro)
     */
    private var player: ExoPlayer? = null
    private var playWhenReadyPlayer = true

    /**
     * The [AudioAttributes] handle the audio focus of the [player]
     */
    private lateinit var audioAttributes: AudioAttributes

    /**
     * SponsorBlock Segment data
     */
    private var segmentData: Segments? = null

    /**
     * Notification for the player
     */
    private lateinit var nowPlayingNotification: NowPlayingNotification

    /**
     * Setting the required [notification] for running as a foreground service
     */
    override fun onCreate() {
        super.onCreate()
        if (Build.VERSION.SDK_INT >= 26) {
            val channelId = BACKGROUND_CHANNEL_ID
            val channel = NotificationChannel(
                channelId,
                "Background Service",
                NotificationManager.IMPORTANCE_DEFAULT
            )
            val notificationManager = getSystemService(NOTIFICATION_SERVICE) as NotificationManager
            notificationManager.createNotificationChannel(channel)
            val notification: Notification = Notification.Builder(this, channelId)
                .setContentTitle(getString(R.string.app_name))
                .setContentText(getString(R.string.playingOnBackground)).build()
            startForeground(PLAYER_NOTIFICATION_ID, notification)
        }
    }

    /**
     * Initializes the [player] with the [MediaItem].
     */
    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
        try {
            // get the intent arguments
            videoId = intent?.getStringExtra("videoId")!!
            val position = intent.getLongExtra("position", 0L)

            // play the audio in the background
            playAudio(videoId, position)
        } catch (e: Exception) {
            stopForeground(true)
            stopSelf()
        }
        return super.onStartCommand(intent, flags, startId)
    }

    /**
     * Gets the video data and prepares the [player].
     */
    private fun playAudio(
        videoId: String,
        seekToPosition: Long = 0
    ) {
        runBlocking {
            val job = launch {
                response = RetrofitInstance.api.getStreams(videoId)
            }
            // Wait until the job is done, to load correctly later in the player
            job.join()

            initializePlayer()
            setMediaItem()

            // create the notification
            if (!this@BackgroundMode::nowPlayingNotification.isInitialized) {
                nowPlayingNotification = NowPlayingNotification(this@BackgroundMode, player!!)
            }
            nowPlayingNotification.updatePlayerNotification(response!!)

            player?.apply {
                playWhenReady = playWhenReadyPlayer
                prepare()
            }

            // seek to the previous position if available
            if (seekToPosition != 0L) player?.seekTo(seekToPosition)

            fetchSponsorBlockSegments()
        }
    }

    /**
     * create the player
     */
    private fun initializePlayer() {
        audioAttributes = AudioAttributes.Builder()
            .setUsage(C.USAGE_MEDIA)
            .setContentType(C.CONTENT_TYPE_MUSIC)
            .build()

        if (player == null) {
            player = ExoPlayer.Builder(this)
                .setAudioAttributes(audioAttributes, true)
                .build()
        }

        /**
         * Listens for changed playbackStates (e.g. pause, end)
         * Plays the next video when the current one ended
         */
        player!!.addListener(object : Player.Listener {
            override fun onPlaybackStateChanged(@Player.State state: Int) {
                when (state) {
                    Player.STATE_ENDED -> {
                        val autoplay = PreferenceHelper.getBoolean(PreferenceKeys.AUTO_PLAY, true)
                        if (autoplay) playNextVideo()
                    }
                    Player.STATE_IDLE -> {
                        onDestroy()
                    }
                }
            }
        })
    }

    /**
     * Plays the first related video to the current (used when the playback of the current video ended)
     */
    private fun playNextVideo() {
        if (response!!.relatedStreams!!.isNotEmpty()) {
            val videoId = response!!
                .relatedStreams!![0].url.toID()

            // play new video on background
            this.videoId = videoId
            this.segmentData = null
            playAudio(videoId)
        }
    }

    /**
     * Sets the [MediaItem] with the [response] into the [player]. Also creates a [MediaSessionConnector]
     * with the [mediaSession] and attach it to the [player].
     */
    private fun setMediaItem() {
        response?.let {
            val mediaItem = MediaItem.Builder().setUri(it.hls!!).build()
            player?.setMediaItem(mediaItem)
        }
    }

    /**
     * fetch the segments for SponsorBlock
     */
    private fun fetchSponsorBlockSegments() {
        CoroutineScope(Dispatchers.IO).launch {
            kotlin.runCatching {
                val categories = PlayerHelper.getSponsorBlockCategories()
                if (categories.size > 0) {
                    segmentData =
                        RetrofitInstance.api.getSegments(
                            videoId,
                            ObjectMapper().writeValueAsString(categories)
                        )
                    checkForSegments()
                }
            }
        }
    }

    /**
     * check for SponsorBlock segments
     */
    private fun checkForSegments() {
        Handler(Looper.getMainLooper()).postDelayed(this::checkForSegments, 100)

        if (segmentData == null || segmentData!!.segments.isEmpty()) return

        segmentData!!.segments.forEach { segment: Segment ->
            val segmentStart = (segment.segment!![0] * 1000f).toLong()
            val segmentEnd = (segment.segment[1] * 1000f).toLong()
            val currentPosition = player?.currentPosition
            if (currentPosition in segmentStart until segmentEnd) {
                player?.seekTo(segmentEnd)
            }
        }
    }

    /**
     * destroy the [BackgroundMode] foreground service
     */
    override fun onDestroy() {
        // called when the user pressed stop in the notification
        // stop the service from being in the foreground and remove the notification
        stopForeground(true)
        // destroy the service
        stopSelf()
        if (this::nowPlayingNotification.isInitialized) nowPlayingNotification.destroy()
        super.onDestroy()
    }

    override fun onBind(p0: Intent?): IBinder? {
        TODO("Not yet implemented")
    }
}