AudioAndListener.swift

//
//  MidiPlayer.swift
//  harmonic
//
//  Created by David Floegel on 03/07/2020.
//

import Foundation
import AudioKit
import UIKit

@objc(MidiPlayer)
class MidiPlayer: RCTEventEmitter {
  var isSetUp = false
  var mixer = AKMixer()
  
  // playback =
  var sequencer = AKSequencer()
  var sampler = AKAppleSampler()
  var noteNumbers: [NSNumber] = []
  
  // listening
  var tracker: AKFrequencyTracker!
  var startTime: TimeInterval = 0
  var recordedFrequencies: [[Double]] = []
  var timer: Timer?
  
  override init() {
    super.init()
  }
  
  @objc
  func setupSynth() {
    if (isSetUp) {
      print("Synth already setup")
      return;
    }
    
    print("Setup synth")
    
    try? AudioKit.stop()
    try? AKSettings.setSession(category: .playAndRecord)
    AKSettings.playbackWhileMuted = true
    AKSettings.defaultToSpeaker = true
    
    try? sampler.loadSoundFont("UprightPiano", preset: 0, bank: 0)
    
    sequencer = AKSequencer(targetNode: sampler)
    
    sampler.setOutput(to: self.mixer)
    
    // ------------------------------------
    let microphone = AKMicrophone()
    let filter = AKLowPassFilter(microphone, cutoffFrequency: 20000, resonance: 0)
    self.tracker = AKFrequencyTracker(filter)
    let silence = AKBooster(tracker, gain: 0)
    self.tracker.stop()
    silence.setOutput(to: self.mixer) // set output to mixer
    AKSettings.audioInputEnabled = true
//
    AudioKit.output = self.mixer
    
    do {
      try AudioKit.start()
    } catch {
      print("start audio kit")
      print(error)
    }
    
    self.isSetUp = true
  }
  
  @objc
  func destroySynth() {
    print("Destroy synth")
    if (self.isSetUp) {
      do {
        try AudioKit.stop()
        AKSettings.audioInputEnabled = false
        self.isSetUp = false
      } catch {
        print(error)
      }
    }
  }

  @objc
  func playNotation(_ bpm: NSNumber, midiNotes: [NSDictionary]) {
    sequencer.tracks[0].clear()
    
    for (i, note) in midiNotes.enumerated() {
      sequencer.tracks[0].add(
        noteNumber: UInt8(truncating: note["midiValue"] as! NSNumber),
        velocity: 100,
        position: Double(i),
        duration: Double(truncating: note["duration"] as! NSNumber) / 1000
      )
      
      noteNumbers.append(note["midiValue"] as! NSNumber)
    }

    // TODO for some reason this doesn't correspond to the total of note durations
    // it's also very unclear whether this is milliseconds, or seconds, or whatever.
    sequencer.length = 600 // sequencer.tracks[0].length
    sequencer.tempo = Double(truncating: bpm)
    sequencer.loopEnabled = false
    sequencer.playFromStart()
  }
  
  @objc
  func stopNotation() {
    sequencer.tracks[0].stop()
    sequencer.stop()
    
    for (note) in self.noteNumbers {
      try? self.sampler.stop(noteNumber: UInt8(truncating: note), channel: 0)
    }
  }
  
  @objc
  func startListening() {
    print("Start listening")
    
    self.startTime = NSDate().timeIntervalSince1970
    self.tracker.start()
    
    DispatchQueue.main.async(execute: {
      self.timer = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector: #selector(self.collectFrequencies), userInfo: nil, repeats: true)
    })
  }
  
  @objc
  func stopListening() {
    print("Stop listening")
    
    self.timer?.invalidate()
    self.tracker.stop()
    self.recordedFrequencies = [];
    AKSettings.audioInputEnabled = false
  }
  
  @objc
  func collectFrequencies() {
    if (self.tracker != nil && self.tracker.isStarted) {
      let f = self.tracker.frequency
      let a = self.tracker.amplitude
      let t = NSDate().timeIntervalSince1970 - self.startTime
      if f > 100 && f <= 2000 {
        self.recordedFrequencies.append([t * 1000, f, a])
        
        self.sendEvent(withName: "readFrequency", body: f)
      }
    }
  }
  
  @objc
  func getFrequencies(_ callback: RCTResponseSenderBlock) {
    callback([self.recordedFrequencies])
  }

  @objc
  override static func requiresMainQueueSetup() -> Bool {
    return true
  }
  
  // Thread 1: Exception: "Error when sending event: readFrequency with body: 117.23126983642578. Bridge is not set. This is probably because you've explicitly synthesized the bridge in MidiPlayer, even though it's inherited from RCTEventEmitter."
  // what's that?
  @objc override func supportedEvents() -> [String]! {
    return ["readFrequency"]
  }
}