SwiftAudioPlayer/Source/Engine/AudioEngine.swift

//
//  AudioEngine.swift
//  SwiftAudioPlayer
//
//  Created by Tanha Kabir on 2019-01-29.
//  Copyright © 2019 Tanha Kabir, Jon Mercer
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.

import Foundation
import AVFoundation

protocol AudioEngineProtocol {
    var key: Key { get }
    var engine: AVAudioEngine! { get }
    func play()
    func pause()
    func seek(toNeedle needle: Needle)
    func invalidate()
}

protocol AudioEngineDelegate: AnyObject {
    func didError()
}

class AudioEngine: AudioEngineProtocol {
    weak var delegate:AudioEngineDelegate?
    var key:Key
    
    var engine: AVAudioEngine!
    var playerNode: AVAudioPlayerNode!
    private var engineInvalidated: Bool = false
    
    static let defaultEngineAudioFormat: AVAudioFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: 44100, channels: 2, interleaved: false)!
    
    var state:TimerState = .suspended
    enum TimerState {
        case suspended
        case resumed
    }
    
    var needle: Needle = -1 {
        didSet {
            if needle >= 0 && oldValue != needle {
                AudioClockDirector.shared.needleTick(key, needle: needle)
            }
        }
    }
    
    var duration: Duration = -1 {
        didSet {
            if duration >= 0 && oldValue != duration {
                AudioClockDirector.shared.durationWasChanged(key, duration: duration)
            }
        }
    }
    
    var playingStatus: SAPlayingStatus? = nil {
        didSet {
            guard playingStatus != oldValue, let status = playingStatus else {
                return
            }
 
            AudioClockDirector.shared.audioPlayingStatusWasChanged(key, status: status)
        }
    }
    
    var bufferedSecondsDebouncer: SAAudioAvailabilityRange = SAAudioAvailabilityRange(startingNeedle: 0.0, durationLoadedByNetwork: 0.0, predictedDurationToLoad: Double.greatestFiniteMagnitude, isPlayable: false)
    var bufferedSeconds: SAAudioAvailabilityRange =  SAAudioAvailabilityRange(startingNeedle: 0.0, durationLoadedByNetwork: 0.0, predictedDurationToLoad: Double.greatestFiniteMagnitude, isPlayable: false) {
        didSet {
            if bufferedSeconds.startingNeedle == 0.0 && bufferedSeconds.durationLoadedByNetwork == 0.0 {
                bufferedSecondsDebouncer = bufferedSeconds
                AudioClockDirector.shared.changeInAudioBuffered(key, buffered: bufferedSeconds)
                return
            }
            
            if bufferedSeconds.startingNeedle == oldValue.startingNeedle && bufferedSeconds.durationLoadedByNetwork == oldValue.durationLoadedByNetwork {
                return
            }
            
            if bufferedSeconds.durationLoadedByNetwork - DEBOUNCING_BUFFER_TIME < bufferedSecondsDebouncer.durationLoadedByNetwork {
                Log.debug("skipping pushing buffer: \(bufferedSeconds)")
                return
            }
            
            bufferedSecondsDebouncer = bufferedSeconds
            AudioClockDirector.shared.changeInAudioBuffered(key, buffered: bufferedSeconds)
        }
    }

    private var audioModifiers: [AVAudioUnit]?
    
    init(url: AudioURL, delegate:AudioEngineDelegate?, engineAudioFormat: AVAudioFormat) {
        self.key = url.key
        self.delegate = delegate
        
        engine = AVAudioEngine()
        playerNode = AVAudioPlayerNode()
        
        initHelper(engineAudioFormat)
    }
    
    func initHelper(_ engineAudioFormat: AVAudioFormat) {
        engine.attach(playerNode)
        audioModifiers = SAPlayer.shared.audioModifiers

        defer { engine.prepare() }

        guard let audioModifiers = audioModifiers, audioModifiers.count > 0 else {
            engine.connect(playerNode, to: engine.mainMixerNode, format: engineAudioFormat)
            return
        }
        
        audioModifiers.forEach { engine.attach($0) }
        
        var i = 0

        let node = audioModifiers[i]
        engine.connect(playerNode, to: node, format: engineAudioFormat)

        i += 1

        while i < audioModifiers.count {
            let lastNode = audioModifiers[i - 1]
            let currNode = audioModifiers[i]

            engine.connect(lastNode, to: currNode, format: engineAudioFormat)
            i += 1
        }

        let finalNode = audioModifiers[audioModifiers.count - 1]

        engine.connect(finalNode, to: engine.mainMixerNode, format: engineAudioFormat)
    }
    
    deinit {
        if state == .resumed {
            playerNode.stop()
            engine.stop()
        }
        
        engine.disconnectNodeInput(self.playerNode)
        engine.detach(self.playerNode)
        
        engine = nil
        playerNode = nil
        Log.info("deinit AVAudioEngine for \(key)")
    }
    
    func doRepeatedly(timeInterval: Double, _ closure: @escaping () -> ()) {
        // A common error in AVAudioEngine is 'required condition is false: nil == owningEngine || GetEngine() == owningEngine'
        // where there can only be one instance of engine running at a time and if there is already one when trying to start
        // a new one then this error will be thrown.
        
        // To handle this error we need to make sure we properly dispose of the engine when done using. In the case of timers, a
        // repeating timer will maintain a strong reference to the body even if you state that you wanted a weak reference to self
        // to mitigate this for repeating timers, you can either call timer.invalidate() properly or don't use repeat block timers.
        // To be in better control of references and to mitigate any unforeseen issues, I decided to implement a recurisive version
        // of the repeat block timer so I'm in full control of when to invalidate.
        
        Timer.scheduledTimer(withTimeInterval: timeInterval, repeats: false) { [weak self] (timer: Timer) in
            guard let self = self else { return }
            guard !self.engineInvalidated else {
                self.delegate = nil
                return
            }
            closure()
            self.doRepeatedly(timeInterval: timeInterval, closure)
        }
    }
    
    func updateIsPlaying() {
        if !bufferedSeconds.isPlayable {
            if bufferedSeconds.reachedEndOfAudio(needle: needle) {
                playingStatus = .ended
            } else {
                playingStatus = .buffering
            }
            return
        }
        
        let isPlaying = engine.isRunning && playerNode.isPlaying
        playingStatus = isPlaying ? .playing : .paused
    }
    
    func play() {
        // https://stackoverflow.com/questions/36754934/update-mpremotecommandcenter-play-pause-button
        if !(engine.isRunning) {
            do {
                try engine.start()
                
            } catch let error {
                Log.monitor(error.localizedDescription)
            }
        }
        
        playerNode.play()
        
        if state == .suspended {
            state = .resumed
        }
    }
    
    func pause() {
        // https://stackoverflow.com/questions/36754934/update-mpremotecommandcenter-play-pause-button
        playerNode.pause()
        engine.pause()
        
        if state == .resumed {
            state = .suspended
        }
    }
    
    func seek(toNeedle needle: Needle) {
        fatalError("No implementation for seek inAudioEngine, should be using streaming or disk type")
    }
    
    func invalidate() {
        engineInvalidated = true
        playerNode.stop()
        engine.stop()

        if let audioModifiers = audioModifiers, audioModifiers.count > 0 {
            audioModifiers.forEach { engine.detach($0) }
        }
        Log.info("invalidated engine for key \(key)")
    }
}