Audio recorder with simple interface, Swift 4

AudioRecorder.swift

import Foundation
import AVFoundation

protocol AudioRecorder {
  func checkPermission(completion: ((Bool) -> Void)?)
  
  /// if url is nil audio will be stored to default url
  func record(to url: URL?)
  func stopRecording()
  
  /// if url is nil audio will be played from default url
  func play(from url: URL?)
  func stopPlaying()
  
  func pause()
  func resume()
}

final class AudioRecorderImpl: NSObject, AudioRecorder {
  private let session = AVAudioSession.sharedInstance()
  private var player: AVAudioPlayer?
  private var recorder: AVAudioRecorder?
  private lazy var permissionGranted = false
  private lazy var isRecording = false
  private lazy var isPlaying = false
  private var fileURL: URL?
  private let settings = [
    AVFormatIDKey: Int(kAudioFormatMPEG4AAC),
    AVSampleRateKey: 44100,
    AVNumberOfChannelsKey: 2,
    AVEncoderAudioQualityKey:AVAudioQuality.high.rawValue
  ]
  
  override init() {
    fileURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first?.appendingPathComponent("note.m4a")
  }
  
  func record(to url: URL?) {
    guard permissionGranted,
      let url = url ?? fileURL else { return }
    
    setupRecorder(url: url)
    
    if isRecording {
      stopRecording()
    }
    
    isRecording = true
    recorder?.record()
  }
  
  func stopRecording() {
    isRecording = false
    recorder?.stop()
    try? session.setActive(false)
  }
  
  func play(from url: URL?) {
    guard let url = url ?? fileURL else { return }
    
    setupPlayer(url: url)
    
    if isRecording {
      stopRecording()
    }
    
    if isPlaying {
      stopPlaying()
    }
    
    if FileManager.default.fileExists(atPath: url.path) {
      isPlaying = true
      setupPlayer(url: url)
      player?.play()
    }
  }
  
  func stopPlaying() {
    player?.stop()
  }
  
  func pause() {
    player?.pause()
  }
  
  func resume() {
    if player?.isPlaying == false {
      player?.play()
    }
  }
  
  func checkPermission(completion: ((Bool) -> Void)?) {
    func assignAndInvokeCallback(_ granted: Bool) {
      self.permissionGranted = granted
      completion?(granted)
    }
    
    switch session.recordPermission {
    case .granted:
      assignAndInvokeCallback(true)
      
    case .denied:
      assignAndInvokeCallback(false)
      
    case .undetermined:
      session.requestRecordPermission(assignAndInvokeCallback)
    }
  }
}

extension AudioRecorderImpl: AVAudioRecorderDelegate, AVAudioPlayerDelegate {
  
}

private extension AudioRecorderImpl {
  func setupRecorder(url: URL) {
    guard
      permissionGranted else { return }
    try? session.setCategory(.playback, mode: .default)
    try? session.setActive(true)
    let settings = [
      AVFormatIDKey: Int(kAudioFormatMPEG4AAC),
      AVSampleRateKey: 44100,
      AVNumberOfChannelsKey: 2,
      AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue
    ]
    recorder = try? AVAudioRecorder(url: url, settings: settings)
    recorder?.delegate = self
    recorder?.isMeteringEnabled = true
    recorder?.prepareToRecord()
  }
  
  func setupPlayer(url: URL) {
    player = try? AVAudioPlayer(contentsOf: url)
    player?.delegate = self
    player?.prepareToPlay()
  }
}