New Midi Player

MidiPlayer.swift

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

import Foundation
import AudioKit

@objc(MidiPlayer)
class MidiPlayer: NSObject {
  var sequencer = AKSequencer()
  var sampler = AKAppleSampler()
  var noteNumbers: [NSNumber] = []
  
  override init() {
    super.init()
    
    self.setupSynth()
  }
  
  func setupSynth() {
    try? sampler.loadSoundFont("UprightPiano", preset: 0, bank: 0)
    
    sequencer = AKSequencer(targetNode: sampler)
    
    let _ = sequencer.addTrack(for: sampler)
    
    try? AudioKit.stop()
    AudioKit.output = sampler
    try? AudioKit.start()
  }

  @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
  static func requiresMainQueueSetup() -> Bool {
    return true
  }
}