import AVFoundation
import Foundation

enum RecordingError: LocalizedError {
  case microphoneDenied
  case couldNotStart

  var errorDescription: String? {
    switch self {
    case .microphoneDenied: "Microphone access is off. Enable it in System Settings."
    case .couldNotStart: "The microphone could not start recording."
    }
  }
}

@MainActor
final class AudioRecorder: NSObject, AVAudioRecorderDelegate {
  private var recorder: AVAudioRecorder?
  private var meterTimer: Timer?
  private(set) var fileURL: URL?
  var onLevel: ((Double) -> Void)?

  func start() async throws {
    guard await Self.requestPermission() else { throw RecordingError.microphoneDenied }
    let fileURL = FileManager.default.temporaryDirectory
      .appendingPathComponent("transui-\(UUID().uuidString).wav")
    self.fileURL = fileURL
    let settings: [String: Any] = [
      AVFormatIDKey: Int(kAudioFormatLinearPCM),
      AVSampleRateKey: 16_000,
      AVNumberOfChannelsKey: 1,
      AVLinearPCMBitDepthKey: 16,
      AVLinearPCMIsFloatKey: false,
      AVLinearPCMIsBigEndianKey: false,
    ]
    let recorder = try AVAudioRecorder(url: fileURL, settings: settings)
    recorder.delegate = self
    recorder.isMeteringEnabled = true
    guard recorder.prepareToRecord(), recorder.record() else {
      throw RecordingError.couldNotStart
    }
    self.recorder = recorder
    meterTimer = Timer.scheduledTimer(withTimeInterval: 0.08, repeats: true) { [weak self] _ in
      Task { @MainActor in self?.updateLevel() }
    }
  }

  func stop() -> URL? {
    meterTimer?.invalidate()
    meterTimer = nil
    recorder?.stop()
    recorder = nil
    onLevel?(0)
    let url = fileURL
    fileURL = nil
    return url
  }

  func cancel() {
    let url = stop()
    if let url { try? FileManager.default.removeItem(at: url) }
    fileURL = nil
  }

  private func updateLevel() {
    guard let recorder else { return }
    recorder.updateMeters()
    let decibels = Double(recorder.averagePower(forChannel: 0))
    let normalized = max(0, min(1, pow(10, decibels / 32)))
    onLevel?(normalized)
  }

  private static func requestPermission() async -> Bool {
    switch AVCaptureDevice.authorizationStatus(for: .audio) {
    case .authorized: true
    case .denied, .restricted: false
    case .notDetermined:
      await withCheckedContinuation { continuation in
        AVCaptureDevice.requestAccess(for: .audio) { allowed in
          continuation.resume(returning: allowed)
        }
      }
    @unknown default: false
    }
  }
}