//
//  FolioReaderAudioPlayer.swift
//  FolioReaderKit
//
//  Created by Kevin Jantzer on 1/4/16.
//  Copyright (c) 2015 Folio Reader. All rights reserved.
//

import UIKit
import AVFoundation
import MediaPlayer

open class FolioReaderAudioPlayer: NSObject {

    var isTextToSpeech = false
    var synthesizer: AVSpeechSynthesizer!
    var playing = false
    var player: AVAudioPlayer?
    var currentHref: String!
    var currentFragment: String!
    var currentSmilFile: FRSmilFile!
    var currentAudioFile: String!
    var currentBeginTime: Double!
    var currentEndTime: Double!
    var playingTimer: Timer!
    var registeredCommands = false
    var completionHandler: () -> Void = {}
    var utteranceRate: Float = 0

    fileprivate var book: FRBook
    fileprivate var folioReader: FolioReader

    // MARK: Init

    init(withFolioReader folioReader: FolioReader, book: FRBook) {
        self.book = book
        self.folioReader = folioReader

        super.init()

        UIApplication.shared.beginReceivingRemoteControlEvents()

        // this is needed to the audio can play even when the "silent/vibrate" toggle is on
        let session = AVAudioSession.sharedInstance()
        try? session.setCategory(AVAudioSessionCategoryPlayback)
        try? session.setActive(true)

        self.updateNowPlayingInfo()
    }

    deinit {
        UIApplication.shared.endReceivingRemoteControlEvents()
    }

    // MARK: Reading speed

    func setRate(_ rate: Int) {
        if let player = player {
            switch rate {
            case 0:
                player.rate = 0.5
                break
            case 1:
                player.rate = 1.0
                break
            case 2:
                player.rate = 1.5
                break
            case 3:
                player.rate = 2
                break
            default:
                break
            }

            updateNowPlayingInfo()
        }
        if synthesizer != nil {
            // Need to change between version IOS
            // http://stackoverflow.com/questions/32761786/ios9-avspeechutterance-rate-for-avspeechsynthesizer-issue
            if #available(iOS 9, *) {
                switch rate {
                case 0:
                    utteranceRate = 0.42
                    break
                case 1:
                    utteranceRate = 0.5
                    break
                case 2:
                    utteranceRate = 0.53
                    break
                case 3:
                    utteranceRate = 0.56
                    break
                default:
                    break
                }
            } else {
                switch rate {
                case 0:
                    utteranceRate = 0
                    break
                case 1:
                    utteranceRate = 0.06
                    break
                case 2:
                    utteranceRate = 0.15
                    break
                case 3:
                    utteranceRate = 0.23
                    break
                default:
                    break
                }
            }

            updateNowPlayingInfo()
        }
    }

    // MARK: Play, Pause, Stop controls

    func stop(immediate: Bool = false) {
        playing = false
        if !isTextToSpeech {
            if let player = player , player.isPlaying {
                player.stop()
            }
        } else {
            stopSynthesizer(immediate: immediate, completion: nil)
        }
    }

    func stopSynthesizer(immediate: Bool = false, completion: (() -> Void)? = nil) {
        synthesizer.stopSpeaking(at: immediate ? .immediate : .word)
        completion?()
    }

    @objc func pause() {
        playing = false

        if !isTextToSpeech {
            if let player = player , player.isPlaying {
                player.pause()
            }
        } else {
            if synthesizer.isSpeaking {
                synthesizer.pauseSpeaking(at: .word)
            }
        }
    }

    @objc func togglePlay() {
        isPlaying() ? pause() : play()
    }

    @objc func play() {
        if book.hasAudio {
            guard let currentPage = self.folioReader.readerCenter?.currentPage else { return }
            currentPage.webView?.js("playAudio()")
        } else {
            self.readCurrentSentence()
        }
    }

    func isPlaying() -> Bool {
        return playing
    }

    /**
     Play Audio (href/fragmentID)

     Begins to play audio for the given chapter (href) and text fragment.
     If this chapter does not have audio, it will delay for a second, then attempt to play the next chapter
     */
    func playAudio(_ href: String, fragmentID: String) {
        isTextToSpeech = false

        self.stop()

        let smilFile = book.smilFile(forHref: href)

        // if no smil file for this href and the same href is being requested, we've hit the end. stop playing
        if smilFile == nil && currentHref != nil && href == currentHref {
            return
        }

        playing = true
        currentHref = href
        currentFragment = "#"+fragmentID
        currentSmilFile = smilFile

        // if no smil file, delay for a second, then move on to the next chapter
        if smilFile == nil {
            Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(_autoPlayNextChapter), userInfo: nil, repeats: false)
            return
        }

        let fragment = smilFile?.parallelAudioForFragment(currentFragment)

        if fragment != nil {
            if _playFragment(fragment) {
                startPlayerTimer()
            }
        }
    }

    @objc func _autoPlayNextChapter() {
        // if user has stopped playing, dont play the next chapter
        if isPlaying() == false { return }
        playNextChapter()
    }

    @objc func playPrevChapter() {
        stopPlayerTimer()
        // Wait for "currentPage" to update, then request to play audio
        self.folioReader.readerCenter?.changePageToPrevious {
            if self.isPlaying() {
                self.play()
            } else {
                self.pause()
            }
        }
    }

    @objc func playNextChapter() {
        stopPlayerTimer()
        // Wait for "currentPage" to update, then request to play audio
        self.folioReader.readerCenter?.changePageToNext {
            if self.isPlaying() {
                self.play()
            }
        }
    }


    /**
     Play Fragment of audio

     Once an audio fragment begins playing, the audio clip will continue playing until the player timer detects
     the audio is out of the fragment timeframe.
     */
    @discardableResult fileprivate func _playFragment(_ smil: FRSmilElement?) -> Bool {

        guard let smil = smil else {
            // FIXME: What about the log that the library prints in the console? shouldn’t we disable it? use another library for that or some compiler flags?
            print("no more parallel audio to play")
            self.stop()
            return false
        }

        let textFragment = smil.textElement().attributes["src"]
        let audioFile = smil.audioElement().attributes["src"]

        currentBeginTime = smil.clipBegin()
        currentEndTime = smil.clipEnd()

        // new audio file to play, create the audio player
        if player == nil || (audioFile != nil && audioFile != currentAudioFile) {

            currentAudioFile = audioFile

            let fileURL = currentSmilFile.resource.basePath() + ("/"+audioFile!)
            let audioData = try? Data(contentsOf: URL(fileURLWithPath: fileURL))

            do {

                player = try AVAudioPlayer(data: audioData!)

                guard let player = player else { return false }

                setRate(self.folioReader.currentAudioRate)
                player.enableRate = true
                player.prepareToPlay()
                player.delegate = self

                updateNowPlayingInfo()
            } catch {
                print("could not read audio file:", audioFile ?? "nil")
                return false
            }
        }

        // if player is initialized properly, begin playing
        guard let player = player else { return false }

        // the audio may be playing already, so only set the player time if it is NOT already within the fragment timeframe
        // this is done to mitigate milisecond skips in the audio when changing fragments
        if player.currentTime < currentBeginTime || ( currentEndTime > 0 && player.currentTime > currentEndTime) {
            player.currentTime = currentBeginTime;
            updateNowPlayingInfo()
        }

        player.play()

        // get the fragment ID so we can "mark" it in the webview
        let textParts = textFragment!.components(separatedBy: "#")
        let fragmentID = textParts[1];
        self.folioReader.readerCenter?.audioMark(href: currentHref, fragmentID: fragmentID)

        return true
    }

    /**
     Next Audio Fragment

     Gets the next audio fragment in the current smil file, or moves on to the next smil file
     */
    fileprivate func nextAudioFragment() -> FRSmilElement? {

        guard let smilFile = book.smilFile(forHref: currentHref) else {
            return nil
        }

        let smil = (self.currentFragment == nil ? smilFile.parallelAudioForFragment(nil) : smilFile.nextParallelAudioForFragment(currentFragment))

        if (smil != nil) {
            self.currentFragment = smil?.textElement().attributes["src"]
            return smil
        }

        self.currentHref = self.book.spine.nextChapter(currentHref)?.href
        self.currentFragment = nil
        self.currentSmilFile = smilFile

        guard (self.currentHref != nil) else {
            return nil
        }

        return self.nextAudioFragment()
    }

    func playText(_ href: String, text: String) {
        isTextToSpeech = true
        playing = true
        currentHref = href

        if synthesizer == nil {
            synthesizer = AVSpeechSynthesizer()
            synthesizer.delegate = self
            setRate(self.folioReader.currentAudioRate)
        }

        let utterance = AVSpeechUtterance(string: text)
        utterance.rate = utteranceRate
        utterance.voice = AVSpeechSynthesisVoice(language: self.book.metadata.language)

        if synthesizer.isSpeaking {
            stopSynthesizer()
        }
        synthesizer.speak(utterance)

        updateNowPlayingInfo()
    }

    // MARK: TTS Sentence

    func speakSentence() {
        guard
            let readerCenter = self.folioReader.readerCenter,
            let currentPage = readerCenter.currentPage else {
                return
        }

        let playbackActiveClass = book.playbackActiveClass
        guard let sentence = currentPage.webView?.js("getSentenceWithIndex('\(playbackActiveClass)')") else {
            if (readerCenter.isLastPage() == true) {
                self.stop()
            } else {
                readerCenter.changePageToNext()
            }

            return
        }

        guard let href = readerCenter.getCurrentChapter()?.href else {
            return
        }

        // TODO QUESTION: The previous code made it possible to call `playText` with the parameter `href` being an empty string. Was that valid? should this logic be kept?
        self.playText(href, text: sentence)
    }

    func readCurrentSentence() {
        guard synthesizer != nil else { return speakSentence() }

        if synthesizer.isPaused {
            playing = true
            synthesizer.continueSpeaking()
        } else {
            if synthesizer.isSpeaking {
                stopSynthesizer(immediate: false, completion: {
                    if let currentPage = self.folioReader.readerCenter?.currentPage {
                        currentPage.webView?.js("resetCurrentSentenceIndex()")
                    }
                    self.speakSentence()
                })
            } else {
                speakSentence()
            }
        }
    }

    // MARK: - Audio timing events

    fileprivate func startPlayerTimer() {
        // we must add the timer in this mode in order for it to continue working even when the user is scrolling a webview
        playingTimer = Timer(timeInterval: 0.01, target: self, selector: #selector(playerTimerObserver), userInfo: nil, repeats: true)
        RunLoop.current.add(playingTimer, forMode: RunLoopMode.commonModes)
    }

    fileprivate func stopPlayerTimer() {
        if playingTimer != nil {
            playingTimer.invalidate()
            playingTimer = nil
        }
    }

    @objc func playerTimerObserver() {
        guard let player = player else { return }

        if currentEndTime != nil && currentEndTime > 0 && player.currentTime > currentEndTime {
            _playFragment(self.nextAudioFragment())
        }
    }

    // MARK: - Now Playing Info and Controls

    /**
     Update Now Playing info

     Gets the book and audio information and updates on Now Playing Center
     */
    func updateNowPlayingInfo() {
        var songInfo = [String: AnyObject]()

        // Get book Artwork
        if let coverImage = self.book.coverImage, let artwork = UIImage(contentsOfFile: coverImage.fullHref) {
            let albumArt = MPMediaItemArtwork(image: artwork)
            songInfo[MPMediaItemPropertyArtwork] = albumArt
        }

        // Get book title
        if let title = self.book.title {
            songInfo[MPMediaItemPropertyAlbumTitle] = title as AnyObject?
        }

        // Get chapter name
        if let chapter = getCurrentChapterName() {
            songInfo[MPMediaItemPropertyTitle] = chapter as AnyObject?
        }

        // Get author name
        if let author = self.book.metadata.creators.first {
            songInfo[MPMediaItemPropertyArtist] = author.name as AnyObject?
        }

        // Set player times
        if let player = player , !isTextToSpeech {
            songInfo[MPMediaItemPropertyPlaybackDuration] = player.duration as AnyObject?
            songInfo[MPNowPlayingInfoPropertyPlaybackRate] = player.rate as AnyObject?
            songInfo[MPNowPlayingInfoPropertyElapsedPlaybackTime ] = player.currentTime as AnyObject?
        }

        // Set Audio Player info
        MPNowPlayingInfoCenter.default().nowPlayingInfo = songInfo

        registerCommandsIfNeeded()
    }

    /**
     Get Current Chapter Name

     This is done here and not in ReaderCenter because even though `currentHref` is accurate,
     the `currentPage` in ReaderCenter may not have updated just yet
     */
    func getCurrentChapterName() -> String? {
        guard let chapter = self.folioReader.readerCenter?.getCurrentChapter() else {
            return nil
        }

        currentHref = chapter.href

        for item in (self.book.flatTableOfContents ?? []) {
            if let resource = item.resource , resource.href == currentHref {
                return item.title
            }
        }
        return nil
    }

    /**
     Register commands if needed, check if it's registered to avoid register twice.
     */
    func registerCommandsIfNeeded() {

        guard !registeredCommands else { return }

        let command = MPRemoteCommandCenter.shared()
        command.previousTrackCommand.isEnabled = true
        command.previousTrackCommand.addTarget(self, action: #selector(playPrevChapter))
        command.nextTrackCommand.isEnabled = true
        command.nextTrackCommand.addTarget(self, action: #selector(playNextChapter))
        command.pauseCommand.isEnabled = true
        command.pauseCommand.addTarget(self, action: #selector(pause))
        command.playCommand.isEnabled = true
        command.playCommand.addTarget(self, action: #selector(play))
        command.togglePlayPauseCommand.isEnabled = true
        command.togglePlayPauseCommand.addTarget(self, action: #selector(togglePlay))

        registeredCommands = true
    }
}

// MARK: AVSpeechSynthesizerDelegate

extension FolioReaderAudioPlayer: AVSpeechSynthesizerDelegate {
    public func speechSynthesizer(_ synthesizer: AVSpeechSynthesizer, didCancel utterance: AVSpeechUtterance) {
        completionHandler()
    }
    
    public func speechSynthesizer(_ synthesizer: AVSpeechSynthesizer, didFinish utterance: AVSpeechUtterance) {
        if isPlaying() {
            readCurrentSentence()
        }
    }
}

// MARK: AVAudioPlayerDelegate

extension FolioReaderAudioPlayer: AVAudioPlayerDelegate {
    public func audioPlayerDidFinishPlaying(_ player: AVAudioPlayer, successfully flag: Bool) {
        _playFragment(self.nextAudioFragment())
    }
}