FrequencyListener.swift

//
//  FListener.swift
//  harmonic
//
//  Created by David Floegel on 05/07/2020.
//

import Foundation
import AudioKit

@objc(FListener)
class FListener: NSObject {
  var mic: AKMicrophone!
  var tracker: AKFrequencyTracker!
  var silence: AKBooster!
  var startTime: TimeInterval = 0
  var recordedFrequencies: [[Double]] = []
  
  var timer: Timer?
  
  override init() {
    super.init()
    self.deinitListener()
  }
  
  @objc
  static func requiresMainQueueSetup() -> Bool {
    return true
  }
  
  @objc
  func initListener() {
    try? AudioKit.stop()
    AKSettings.audioInputEnabled = true
    self.mic = AKMicrophone()
    let filter = AKLowPassFilter(self.mic)
    filter.cutoffFrequency = 20000
    filter.resonance = 0
    self.tracker = AKFrequencyTracker(filter)
    self.silence = AKBooster(tracker, gain: 0)
    self.tracker.stop()
    
    AudioKit.output = self.silence
    try? AudioKit.start()
  }
  
  @objc
  func deinitListener() {
    do {
      try AudioKit.stop()
    } catch {
      print(error)
    }
  }
  
  @objc
  func startListening() {
    self.startTime = NSDate().timeIntervalSince1970
    self.tracker.start()
    
    DispatchQueue.main.async(execute: {
      Timer.scheduledTimer(timeInterval: 0.1, target: self, selector: #selector(self.collectFrequencies), userInfo: nil, repeats: true)
      print("Timer started")
    })
  }
  
  @objc
  func stopTracking() {
    self.timer?.invalidate()
    self.tracker.stop()
  }
  
  @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 <= 900 {
        self.recordedFrequencies.append([t, f, a])
      }
    }
  }

  @objc
  func listen(_ callback: RCTResponseSenderBlock) {
    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 <= 900 {
        self.recordedFrequencies.append([t, f, a])
        callback([f, a])
      }
    }
  }
  
  @objc
  func getFrequencies(_ callback: RCTResponseSenderBlock) {
    callback([self.recordedFrequencies])
  }
}