package com.github.libretube.services

import android.app.NotificationManager
import android.app.PendingIntent
import android.app.Service
import android.content.Intent
import android.os.Binder
import android.os.Build
import android.os.IBinder
import androidx.core.app.NotificationCompat
import com.github.libretube.R
import com.github.libretube.api.RetrofitInstance
import com.github.libretube.constants.DOWNLOAD_CHANNEL_ID
import com.github.libretube.constants.DOWNLOAD_PROGRESS_NOTIFICATION_ID
import com.github.libretube.constants.IntentData
import com.github.libretube.db.DatabaseHolder
import com.github.libretube.db.obj.Download
import com.github.libretube.db.obj.DownloadItem
import com.github.libretube.enums.FileType
import com.github.libretube.extensions.awaitQuery
import com.github.libretube.extensions.formatAsFileSize
import com.github.libretube.extensions.getContentLength
import com.github.libretube.extensions.query
import com.github.libretube.extensions.toDownloadItems
import com.github.libretube.extensions.toastFromMainThread
import com.github.libretube.obj.DownloadStatus
import com.github.libretube.receivers.NotificationReceiver
import com.github.libretube.ui.activities.MainActivity
import com.github.libretube.util.DownloadHelper
import com.github.libretube.util.ImageHelper
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.Job
import kotlinx.coroutines.SupervisorJob
import kotlinx.coroutines.flow.MutableSharedFlow
import kotlinx.coroutines.flow.SharedFlow
import kotlinx.coroutines.isActive
import kotlinx.coroutines.launch
import okhttp3.OkHttpClient
import okhttp3.Request
import okio.BufferedSink
import okio.buffer
import okio.sink
import java.io.File
import java.net.URL
import java.util.concurrent.TimeUnit
import kotlin.coroutines.coroutineContext

/**
 * Download service with custom implementation of downloading using [OkHttpClient].
 */
class DownloadService : Service() {

    private val binder = LocalBinder()
    private val jobMain = SupervisorJob()
    private val scope = CoroutineScope(Dispatchers.IO + jobMain)

    private lateinit var notificationManager: NotificationManager
    private lateinit var summaryNotificationBuilder: NotificationCompat.Builder

    private val jobs = mutableMapOf<Int, Job>()
    private val _downloadFlow = MutableSharedFlow<Pair<Int, DownloadStatus>>()
    val downloadFlow: SharedFlow<Pair<Int, DownloadStatus>> = _downloadFlow

    override fun onCreate() {
        super.onCreate()
        IS_DOWNLOAD_RUNNING = true
        notifyForeground()
    }

    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
        when (intent?.action) {
            ACTION_RESUME -> resume(intent.getIntExtra("id", -1))
            ACTION_PAUSE -> pause(intent.getIntExtra("id", -1))
        }

        val videoId = intent?.getStringExtra(IntentData.videoId) ?: return START_NOT_STICKY
        val fileName = intent.getStringExtra(IntentData.fileName) ?: videoId
        val videoFormat = intent.getStringExtra(IntentData.videoFormat)
        val videoQuality = intent.getStringExtra(IntentData.videoQuality)
        val audioFormat = intent.getStringExtra(IntentData.audioFormat)
        val audioQuality = intent.getStringExtra(IntentData.audioQuality)
        val subtitleCode = intent.getStringExtra(IntentData.subtitleCode)

        scope.launch {
            try {
                val streams = RetrofitInstance.api.getStreams(videoId)

                awaitQuery {
                    DatabaseHolder.Database.downloadDao().insertDownload(
                        Download(
                            videoId = videoId,
                            title = streams.title ?: "",
                            thumbnailPath = File(
                                DownloadHelper.getDownloadDir(this@DownloadService, DownloadHelper.THUMBNAIL_DIR),
                                fileName
                            ).absolutePath,
                            description = streams.description ?: "",
                            uploadDate = streams.uploadDate
                        )
                    )
                }
                streams.thumbnailUrl?.let { url ->
                    ImageHelper.downloadImage(this@DownloadService, url, fileName)
                }

                val downloadItems = streams.toDownloadItems(
                    videoId,
                    fileName,
                    videoFormat,
                    videoQuality,
                    audioFormat,
                    audioQuality,
                    subtitleCode
                )
                downloadItems.forEach { start(it) }
            } catch (e: Exception) {
                return@launch
            }
        }

        return START_NOT_STICKY
    }

    /**
     * Initiate download [Job] using [DownloadItem] by creating file according to [FileType]
     * for the requested file.
     */
    private fun start(item: DownloadItem) {
        val file: File = when (item.type) {
            FileType.AUDIO -> {
                val audioDownloadDir = DownloadHelper.getDownloadDir(
                    this,
                    DownloadHelper.AUDIO_DIR
                )
                File(audioDownloadDir, item.fileName)
            }
            FileType.VIDEO -> {
                val videoDownloadDir = DownloadHelper.getDownloadDir(
                    this,
                    DownloadHelper.VIDEO_DIR
                )
                File(videoDownloadDir, item.fileName)
            }
            FileType.SUBTITLE -> {
                val subtitleDownloadDir = DownloadHelper.getDownloadDir(
                    this,
                    DownloadHelper.SUBTITLE_DIR
                )
                File(subtitleDownloadDir, item.fileName)
            }
        }
        file.createNewFile()
        item.path = file.absolutePath

        item.id = awaitQuery {
            DatabaseHolder.Database.downloadDao().insertDownloadItem(item)
        }.toInt()

        jobs[item.id] = scope.launch {
            downloadFile(item)
        }
    }

    /**
     * Download file and emit [DownloadStatus] to the collectors of [downloadFlow]
     * and notification.
     */
    private suspend fun downloadFile(item: DownloadItem) {
        val notificationBuilder = getNotificationBuilder(item)
        setResumeNotification(notificationBuilder, item)

        val okHttpClient = OkHttpClient.Builder()
            .connectTimeout(DownloadHelper.DEFAULT_TIMEOUT, TimeUnit.SECONDS)
            .readTimeout(DownloadHelper.DEFAULT_TIMEOUT, TimeUnit.SECONDS)
            .build()

        val file = File(item.path)
        var totalRead = file.length()
        val url = URL(item.url ?: return)

        url.getContentLength().let { size ->
            if (size > 0 && size != item.downloadSize) {
                item.downloadSize = size
                query {
                    DatabaseHolder.Database.downloadDao().updateDownloadItem(item)
                }
            }
        }

        // Set start range where last downloading was held.
        val request = Request.Builder()
            .url(url)
            .addHeader("Range", "bytes=$totalRead-").build()
        var lastTime = System.currentTimeMillis() / 1000
        var lastRead: Long = 0
        val sink: BufferedSink = file.sink(true).buffer()

        try {
            val response = okHttpClient.newCall(request).execute()
            val sourceBytes = response.body!!.source()

            // Check if job is still active and read next bytes.
            while (coroutineContext.isActive &&
                sourceBytes
                    .read(sink.buffer, DownloadHelper.DOWNLOAD_CHUNK_SIZE)
                    .also { lastRead = it } != -1L
            ) {
                sink.emit()
                totalRead += lastRead
                _downloadFlow.emit(item.id to DownloadStatus.Progress(totalRead, item.downloadSize))

                if (item.downloadSize != -1L &&
                    System.currentTimeMillis() / 1000 > lastTime
                ) {
                    notificationBuilder
                        .setContentText("${totalRead.formatAsFileSize()} / ${item.downloadSize.formatAsFileSize()}")
                        .setProgress(item.downloadSize.toInt(), totalRead.toInt(), false)
                    notificationManager.notify(item.id, notificationBuilder.build())
                    lastTime = System.currentTimeMillis() / 1000
                }
            }
        } catch (e: Exception) {
            toastFromMainThread("${getString(R.string.download)}: ${e.message.toString()}")
            _downloadFlow.emit(item.id to DownloadStatus.Error(e.message.toString(), e))
        } finally {
            sink.flush()
            sink.close()
        }

        val completed = when (totalRead) {
            item.downloadSize -> {
                _downloadFlow.emit(item.id to DownloadStatus.Completed)
                true
            }
            else -> {
                _downloadFlow.emit(item.id to DownloadStatus.Paused)
                false
            }
        }
        pause(item.id)
        setPauseNotification(notificationBuilder, item, completed)
    }

    /**
     * Resume download which may have been paused.
     */
    fun resume(id: Int) {
        // Cancel last job if it is still active to avoid multiple
        // jobs for same file.
        jobs[id]?.cancel()
        val downloadItem = awaitQuery {
            DatabaseHolder.Database.downloadDao().findDownloadItemById(id)
        }
        jobs[id] = scope.launch {
            downloadFile(downloadItem)
        }
    }

    /**
     * Pause downloading job for given [id]. If no [jobs] are active, stop the service.
     */
    fun pause(id: Int) {
        jobs[id]?.cancel()

        // Stop the service if no downloads are active.
        if (jobs.values.none { it.isActive }) {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
                stopForeground(STOP_FOREGROUND_DETACH)
            }
            stopSelf()
        }
    }

    /**
     * Check whether the file downloading job is active or not.
     */
    fun isDownloading(id: Int): Boolean {
        return jobs[id]?.isActive ?: false
    }

    private fun notifyForeground() {
        notificationManager = getSystemService(NOTIFICATION_SERVICE) as NotificationManager

        summaryNotificationBuilder = NotificationCompat
            .Builder(this, DOWNLOAD_CHANNEL_ID)
            .setSmallIcon(R.mipmap.ic_launcher)
            .setContentTitle(getString(R.string.downloading))
            .setForegroundServiceBehavior(NotificationCompat.FOREGROUND_SERVICE_IMMEDIATE)
            .setGroup(DOWNLOAD_NOTIFICATION_GROUP)
            .setPriority(NotificationCompat.PRIORITY_LOW)
            .setOnlyAlertOnce(true)
            .setGroupSummary(true)

        startForeground(DOWNLOAD_PROGRESS_NOTIFICATION_ID, summaryNotificationBuilder.build())
    }

    private fun getNotificationBuilder(item: DownloadItem): NotificationCompat.Builder {
        val flag = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            PendingIntent.FLAG_IMMUTABLE
        } else {
            0
        }

        val activityIntent =
            PendingIntent.getActivity(
                this@DownloadService,
                0,
                Intent(this@DownloadService, MainActivity::class.java).apply {
                    putExtra("fragmentToOpen", "downloads")
                },
                flag
            )

        return NotificationCompat
            .Builder(this, DOWNLOAD_CHANNEL_ID)
            .setContentTitle(getString(R.string.downloading))
            .setProgress(0, 0, true)
            .setOngoing(true)
            .setContentIntent(activityIntent)
            .setForegroundServiceBehavior(NotificationCompat.FOREGROUND_SERVICE_IMMEDIATE)
            .setGroupAlertBehavior(NotificationCompat.GROUP_ALERT_SUMMARY)
            .setGroup(DOWNLOAD_NOTIFICATION_GROUP)
    }

    private fun setResumeNotification(notificationBuilder: NotificationCompat.Builder, item: DownloadItem) {
        notificationBuilder
            .setContentTitle(item.fileName)
            .setSmallIcon(android.R.drawable.stat_sys_download)
            .setWhen(System.currentTimeMillis())
            .setOngoing(true)
            .clearActions()
            .addAction(getPauseAction(item.id))

        notificationManager.notify(item.id, notificationBuilder.build())
    }

    private fun setPauseNotification(notificationBuilder: NotificationCompat.Builder, item: DownloadItem, isCompleted: Boolean = false) {
        notificationBuilder
            .setProgress(0, 0, false)
            .setOngoing(false)
            .clearActions()

        if (isCompleted) {
            notificationBuilder
                .setSmallIcon(R.drawable.ic_done)
                .setContentText(getString(R.string.download_completed))
        } else {
            notificationBuilder
                .setSmallIcon(R.drawable.ic_pause)
                .setContentText(getString(R.string.download_paused))
                .addAction(getResumeAction(item.id))
        }
        notificationManager.notify(item.id, notificationBuilder.build())
    }

    private fun getResumeAction(id: Int): NotificationCompat.Action {
        val intent = Intent(this, NotificationReceiver::class.java)

        intent.action = ACTION_RESUME
        intent.putExtra("id", id)

        val flags = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            (PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE)
        } else {
            PendingIntent.FLAG_UPDATE_CURRENT
        }

        return NotificationCompat.Action.Builder(
            R.drawable.ic_play,
            getString(R.string.resume),
            PendingIntent.getBroadcast(this, id, intent, flags)
        ).build()
    }

    private fun getPauseAction(id: Int): NotificationCompat.Action {
        val intent = Intent(this, NotificationReceiver::class.java)

        intent.action = ACTION_PAUSE
        intent.putExtra("id", id)

        val flags = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            (PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE)
        } else {
            PendingIntent.FLAG_UPDATE_CURRENT
        }

        return NotificationCompat.Action.Builder(
            R.drawable.ic_pause,
            getString(R.string.pause),
            PendingIntent.getBroadcast(this, id, intent, flags)
        ).build()
    }

    override fun onDestroy() {
        jobMain.cancel()
        IS_DOWNLOAD_RUNNING = false
        super.onDestroy()
    }

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

    inner class LocalBinder : Binder() {
        fun getService(): DownloadService = this@DownloadService
    }

    companion object {
        private const val DOWNLOAD_NOTIFICATION_GROUP = "download_notification_group"
        const val ACTION_RESUME = "com.github.libretube.services.DownloadService.ACTION_RESUME"
        const val ACTION_PAUSE = "com.github.libretube.services.DownloadService.ACTION_PAUSE"
        var IS_DOWNLOAD_RUNNING = false
    }
}