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

package com.github.libretube

import android.content.Context
import android.support.v4.media.session.MediaSessionCompat
import com.github.libretube.obj.Streams
import com.google.android.exoplayer2.C
import com.google.android.exoplayer2.ExoPlayer
import com.google.android.exoplayer2.MediaItem
import com.google.android.exoplayer2.audio.AudioAttributes
import com.google.android.exoplayer2.ext.mediasession.MediaSessionConnector
import com.google.android.exoplayer2.ui.PlayerNotificationManager
import kotlinx.coroutines.launch
import kotlinx.coroutines.runBlocking

/**
 * Loads the selected video audio in background mode with a notification area.
 */
class BackgroundMode {
    /**
     * 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 [MediaSessionCompat] for the [response].
     */
    private lateinit var mediaSession: MediaSessionCompat

    /**
     * The [MediaSessionConnector] to connect with the [mediaSession] and implement it with the [player].
     */
    private lateinit var mediaSessionConnector: MediaSessionConnector

    /**
     * The [PlayerNotificationManager] to load the [mediaSession] content on it.
     */
    private lateinit var playerNotification: PlayerNotificationManager

    /**
     * Initializes the [player] with the [MediaItem].
     */
    private fun initializePlayer(c: Context) {
        /**
         * The [audioAttributes] handle the audio focus of the [player]
         */
        val audioAttributes = AudioAttributes.Builder()
            .setUsage(C.USAGE_MEDIA)
            .setContentType(C.CONTENT_TYPE_MUSIC)
            .build()

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

    /**
     * Initializes the [playerNotification] attached to the [player] and shows it.
     */
    private fun initializePlayerNotification(c: Context) {
        playerNotification = PlayerNotificationManager
            .Builder(c, 1, "background_mode").build()
        playerNotification.setPlayer(player)
        playerNotification.setUsePreviousAction(false)
        playerNotification.setUseNextAction(false)
        playerNotification.setMediaSessionToken(mediaSession.sessionToken)
    }

    /**
     * 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(c: Context) {
        response?.let {
            val mediaItem = MediaItem.Builder().setUri(it.hls!!).build()
            player?.setMediaItem(mediaItem)
        }

        mediaSession = MediaSessionCompat(c, this.javaClass.name)
        mediaSession.isActive = true

        mediaSessionConnector = MediaSessionConnector(mediaSession)
        mediaSessionConnector.setPlayer(player)
    }

    /**
     * Gets the video data and prepares the [player].
     */
    fun playOnBackgroundMode(c: Context, videoId: String, seekToPosition: Long) {
        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(c)
            initializePlayerNotification(c)

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

            if (!seekToPosition.equals(0)) player?.seekTo(seekToPosition)
        }
    }

    /**
     * Creates a singleton of this class, to not create a new [player] every time.
     */
    companion object {
        private var INSTANCE: BackgroundMode? = null

        fun getInstance(): BackgroundMode {
            if (INSTANCE == null) INSTANCE = BackgroundMode()
            return INSTANCE!!
        }
    }
}