//
//  RegularPlayer.swift
//  Pods
//
//  Created by King, Gavin on 3/7/17.
//
//

import Foundation
import AVFoundation
import AVKit

extension AVMediaSelectionOption: TextTrackMetadata {
    public var isSDHTrack: Bool {
        return self.hasMediaCharacteristic(.describesMusicAndSoundForAccessibility) && self.hasMediaCharacteristic(.transcribesSpokenDialogForAccessibility)
    }
}

/// A RegularPlayer is used to play regular videos.
@objc open class RegularPlayer: NSObject, Player, ProvidesView {
    public struct Constants {
        public static let TimeUpdateInterval: TimeInterval = 0.1
    }
    
    // MARK: - Private Properties
    
    fileprivate var player = AVPlayer()

    private var regularPlayerView: RegularPlayerView

    private var playerLayer: AVPlayerLayer {
        return self.regularPlayerView.playerLayer
    }

    private var seekTolerance: CMTime?

    private var seekTarget: CMTime = CMTime.invalid
    private var isSeekInProgress: Bool = false
    
    // MARK: - Public API
    
    /// Sets an AVAsset on the player.
    ///
    /// - Parameter asset: The AVAsset
    @objc open func set(_ asset: AVAsset) {
        let playerItem = AVPlayerItem(asset: asset)
        self.set(playerItem: playerItem)
    }

    @objc open func set(playerItem: AVPlayerItem) {
        // Prepare the old item for removal
        if let currentItem = self.player.currentItem {
            self.removePlayerItemObservers(fromPlayerItem: currentItem)
        }

        // Replace it with the new item
        self.addPlayerItemObservers(toPlayerItem: playerItem)
        self.player.replaceCurrentItem(with: playerItem)
    }
    
    // MARK: - ProvidesView
    
    private class RegularPlayerView: PlayerView {
        var playerLayer: AVPlayerLayer {
            return self.layer as! AVPlayerLayer
        }

        #if canImport(UIKit)
        override class var layerClass: AnyClass {
            return AVPlayerLayer.self
        }
        #elseif canImport(AppKit)
        override init(frame frameRect: NSRect) {
            super.init(frame: frameRect)
            self.layer = AVPlayerLayer()
        }

        required init?(coder decoder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
        #endif
        
        func configureForPlayer(player: AVPlayer) {
            (self.layer as! AVPlayerLayer).player = player
        }
    }
    
    open var view: UIView {
        return self.regularPlayerView
    }
    
    // MARK: - Player
    
    weak public var delegate: PlayerDelegate?
    
    public private(set) var state: PlayerState = .ready {
        didSet {
            self.delegate?.playerDidUpdateState(player: self, previousState: oldValue)
        }
    }
    
    public var duration: TimeInterval {
        return self.player.currentItem?.duration.timeInterval ?? 0
    }
    
    public private(set) var time: TimeInterval = 0 {
        didSet {
            self.delegate?.playerDidUpdateTime(player: self)
        }
    }
    
    public private(set) var bufferedTime: TimeInterval = 0 {
        didSet {
            self.delegate?.playerDidUpdateBufferedTime(player: self)
        }
    }
    
    public var playing: Bool {
        return self.player.rate > 0
    }
    
    public var ended: Bool {
        return self.time >= self.duration
    }
    
    public var error: NSError? {
        return self.player.errorForPlayerOrItem
    }
    
    open func seek(to time: TimeInterval) {
        let cmTime = CMTimeMakeWithSeconds(time, preferredTimescale: Int32(NSEC_PER_SEC))
        self.smoothSeek(to: cmTime)
    }

    open func play() {
        self.player.play()
    }
    
    open func pause() {
        self.player.pause()
    }
    
    // MARK: - Lifecycle

    override public convenience init() {
        self.init(seekTolerance: nil)
    }
    
    public init(seekTolerance: TimeInterval?) {
        self.regularPlayerView = RegularPlayerView(frame: .zero)
        self.seekTolerance = seekTolerance.map {
            CMTimeMakeWithSeconds($0, preferredTimescale: Int32(NSEC_PER_SEC))
        }

        super.init()
        
        self.addPlayerObservers()
        self.regularPlayerView.configureForPlayer(player: self.player)
        self.setupAirplay()
    }
    
    deinit {
        if let playerItem = self.player.currentItem {
            self.removePlayerItemObservers(fromPlayerItem: playerItem)
        }
        
        self.removePlayerObservers()
    }
    
    // MARK: - Setup

    @available(iOS 10.0, tvOS 10.0, macOS 10.12, *)
    public var automaticallyWaitsToMinimizeStalling: Bool {
        get {
            return self.player.automaticallyWaitsToMinimizeStalling
        }
        set {
            self.player.automaticallyWaitsToMinimizeStalling = newValue
        }
    }
    
    private func setupAirplay() {
        #if os(iOS) || os(tvOS)
            self.player.usesExternalPlaybackWhileExternalScreenIsActive = true
        #endif
    }

    // MARK: - Smooth Seeking

    // Note: Smooth seeking follows the guide from Apple Technical Q&A: https://developer.apple.com/library/archive/qa/qa1820/_index.html
    // Update the seek target and begin seeking if there is no seek currently in progress.
    private func smoothSeek(to cmTime: CMTime) {
        self.seekTarget = cmTime

        guard self.isSeekInProgress == false else { return }
        self.seekToTarget()
    }

    // Unconditionally seek to the current seek target.
    private func seekToTarget() {
        self.isSeekInProgress = true

        guard self.player.status != .unknown else { return }

        assert(CMTIME_IS_VALID(self.seekTarget))
        let inProgressSeekTarget = self.seekTarget

        let completion: (Bool) -> Void = { [weak self] _ in
            guard let self = self else { return }

            self.time = CMTimeGetSeconds(inProgressSeekTarget)
            if CMTimeCompare(inProgressSeekTarget, self.seekTarget) == 0 {
                self.isSeekInProgress = false
            } else {
                self.seekToTarget()
            }
        }

        if let tolerance = self.seekTolerance {
            self.player.seek(
                to: inProgressSeekTarget,
                toleranceBefore: tolerance,
                toleranceAfter: tolerance,
                completionHandler: completion
            )
        } else {
            self.player.seek(to: inProgressSeekTarget, completionHandler: completion)
        }
    }

    
    // MARK: - Observers
    
    private struct KeyPath {
        struct Player {
            static let Rate = "rate"
        }
        
        struct PlayerItem {
            static let Status = "status"
            static let PlaybackLikelyToKeepUp = "playbackLikelyToKeepUp"
            static let LoadedTimeRanges = "loadedTimeRanges"
        }
    }
    
    private var playerTimeObserver: Any?
    
    private func addPlayerItemObservers(toPlayerItem playerItem: AVPlayerItem) {
        playerItem.addObserver(self, forKeyPath: KeyPath.PlayerItem.Status, options: [.initial, .new], context: nil)
        playerItem.addObserver(self, forKeyPath: KeyPath.PlayerItem.PlaybackLikelyToKeepUp, options: [.initial, .new], context: nil)
        playerItem.addObserver(self, forKeyPath: KeyPath.PlayerItem.LoadedTimeRanges, options: [.initial, .new], context: nil)
    }
    
    private func removePlayerItemObservers(fromPlayerItem playerItem: AVPlayerItem) {
        playerItem.removeObserver(self, forKeyPath: KeyPath.PlayerItem.Status, context: nil)
        playerItem.removeObserver(self, forKeyPath: KeyPath.PlayerItem.PlaybackLikelyToKeepUp, context: nil)
        playerItem.removeObserver(self, forKeyPath: KeyPath.PlayerItem.LoadedTimeRanges, context: nil)
    }
    
    private func addPlayerObservers() {
        self.player.addObserver(self, forKeyPath: KeyPath.Player.Rate, options: [.initial, .new], context: nil)
        
        let interval = CMTimeMakeWithSeconds(Constants.TimeUpdateInterval, preferredTimescale: Int32(NSEC_PER_SEC))
        
        self.playerTimeObserver = self.player.addPeriodicTimeObserver(forInterval: interval, queue: DispatchQueue.main, using: { [weak self] (cmTime) in
            
            if let strongSelf = self, let time = cmTime.timeInterval {
                strongSelf.time = time
            }
        })
    }
    
    private func removePlayerObservers() {
        self.player.removeObserver(self, forKeyPath: KeyPath.Player.Rate, context: nil)
        
        if let playerTimeObserver = self.playerTimeObserver {
            self.player.removeTimeObserver(playerTimeObserver)
            
            self.playerTimeObserver = nil
        }
    }
    
    // MARK: Observation
    
    override open func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        // Player Item Observers
        
        if keyPath == KeyPath.PlayerItem.Status {
            if let statusInt = change?[.newKey] as? Int, let status = AVPlayerItem.Status(rawValue: statusInt) {
                self.playerItemStatusDidChange(status: status)
            }
        }
        else if keyPath == KeyPath.PlayerItem.PlaybackLikelyToKeepUp {
            if let playbackLikelyToKeepUp = change?[.newKey] as? Bool {
                self.playerItemPlaybackLikelyToKeepUpDidChange(playbackLikelyToKeepUp: playbackLikelyToKeepUp)
            }
        }
        else if keyPath == KeyPath.PlayerItem.LoadedTimeRanges {
            if let loadedTimeRanges = change?[.newKey] as? [NSValue] {
                self.playerItemLoadedTimeRangesDidChange(loadedTimeRanges: loadedTimeRanges)
            }
        }
            
        // Player Observers
            
        else if keyPath == KeyPath.Player.Rate {
            if let rate = change?[.newKey] as? Float {
                self.playerRateDidChange(rate: rate)
            }
        }
            
        // Fall Through Observers
            
        else {
            super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
        }
    }
    
    // MARK: Observation Helpers

    private func playerItemStatusDidChange(status: AVPlayerItem.Status) {
        switch status {
        case .unknown:
            
            self.state = .loading
            
        case .readyToPlay:
            
            self.state = .ready

            // If we tried to seek before the video was ready to play, resume seeking now.
            if self.isSeekInProgress {
                self.seekToTarget()
            }
            
        case .failed:
            
            self.state = .failed
        
        @unknown default:
            
            self.state = .failed
        }
    }
    
    private func playerRateDidChange(rate: Float) {
        self.delegate?.playerDidUpdatePlaying(player: self)
    }
    
    private func playerItemPlaybackLikelyToKeepUpDidChange(playbackLikelyToKeepUp: Bool) {
        let state: PlayerState = playbackLikelyToKeepUp ? .ready : .loading
        
        self.state = state
    }
    
    private func playerItemLoadedTimeRangesDidChange(loadedTimeRanges: [NSValue]) {
        guard let bufferedCMTime = loadedTimeRanges.first?.timeRangeValue.end, let bufferedTime = bufferedCMTime.timeInterval else {
            return
        }
        
        self.bufferedTime = bufferedTime
    }
    
    // MARK: - Capability Protocol Helpers
    
    #if os(iOS)
    @available(iOS 9.0, *)
    fileprivate lazy var _pictureInPictureController: AVPictureInPictureController? = {
        AVPictureInPictureController(playerLayer: self.regularPlayerView.playerLayer)
    }()
    #endif
}

// MARK: Capability Protocols

extension RegularPlayer: AirPlayCapable
{
    public var isAirPlayEnabled: Bool {
        get {
            return self.player.allowsExternalPlayback
        }
        set {
            return self.player.allowsExternalPlayback = newValue
        }
    }
}

#if os(iOS)
extension RegularPlayer: PictureInPictureCapable {
    @available(iOS 9.0, *)
    public var pictureInPictureController: AVPictureInPictureController? {
        return self._pictureInPictureController
    }
}
#endif

extension RegularPlayer: VolumeCapable
{
    public var volume: Float {
        get {
            return self.player.volume
        }
        set {
            self.player.volume = newValue
        }
    }
}

extension RegularPlayer: FillModeCapable {
    public var fillMode: FillMode {
        get {
            let gravity = (self.view.layer as! AVPlayerLayer).videoGravity
            
            return gravity == .resizeAspect ? .fit : .fill
        }
        set {
            let gravity: AVLayerVideoGravity
            
            switch newValue {
            case .fit:
                
                gravity = .resizeAspect
                
            case .fill:
                
                gravity = .resizeAspectFill
            }

            (self.view.layer as! AVPlayerLayer).videoGravity = gravity
        }
    }
}

extension RegularPlayer: TextTrackCapable {
    public var selectedTextTrack: TextTrackMetadata? {
        guard let group = self.player.currentItem?.asset.mediaSelectionGroup(forMediaCharacteristic: .legible) else {
            return nil
        }
        
        if #available(iOS 9.0, *) {
            return self.player.currentItem?.currentMediaSelection.selectedMediaOption(in: group)
        }
        else {
            return self.player.currentItem?.selectedMediaOption(in: group)
        }
    }
    
    public var availableTextTracks: [TextTrackMetadata] {
        guard let group = self.player.currentItem?.asset.mediaSelectionGroup(forMediaCharacteristic: .legible) else {
            return []
        }
        return group.options
    }
    
    public func fetchTextTracks(completion: @escaping ([TextTrackMetadata], TextTrackMetadata?) -> Void) {
        self.player.currentItem?.asset.loadValuesAsynchronously(forKeys: [#keyPath(AVAsset.availableMediaCharacteristicsWithMediaSelectionOptions)]) { [weak self] in
            guard let strongSelf = self, let group = strongSelf.player.currentItem?.asset.mediaSelectionGroup(forMediaCharacteristic: .legible) else {
                completion([], nil)
                return
            }
            if #available(iOS 9.0, *) {
                completion(group.options, strongSelf.player.currentItem?.currentMediaSelection.selectedMediaOption(in: group))
            }
            else {
                completion(group.options, strongSelf.player.currentItem?.selectedMediaOption(in: group))
            }
        }
    }
    
    public func select(_ textTrack: TextTrackMetadata?) {
        guard let group = self.player.currentItem?.asset.mediaSelectionGroup(forMediaCharacteristic: .legible) else {
            return
        }
        
        guard let track = textTrack else {
            self.player.currentItem?.select(nil, in: group)
            return
        }
        
        let option = group.options.first(where: { option in
            track.matches(option)
        })
        self.player.currentItem?.select(option, in: group)
    }
}