import CoreLocation
import Flutter
import UIKit

public class LocationPlugin: NSObject, FlutterPlugin, CLLocationManagerDelegate {
  private let locationManager = CLLocationManager()
  private var pendingResult: FlutterResult?

  override init() {
    super.init()
    locationManager.delegate = self
    locationManager.desiredAccuracy = kCLLocationAccuracyBest
  }

  public static func register(with registrar: FlutterPluginRegistrar) {
    let channel = FlutterMethodChannel(name: "location_plugin", binaryMessenger: registrar.messenger())
    let instance = LocationPlugin()
    registrar.addMethodCallDelegate(instance, channel: channel)
  }

  public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
    switch call.method {
    case "getPlatformVersion":
      result("iOS " + UIDevice.current.systemVersion)
    case "getCurrentLocation":
      requestCurrentLocation(result: result)
    default:
      result(FlutterMethodNotImplemented)
    }
  }

  private func requestCurrentLocation(result: @escaping FlutterResult) {
    guard pendingResult == nil else {
      result(FlutterError(code: "LOCATION_IN_PROGRESS", message: "A previous location request is still running.", details: nil))
      return
    }
    guard CLLocationManager.locationServicesEnabled() else {
      result(FlutterError(code: "LOCATION_DISABLED", message: "Location services are turned off.", details: nil))
      return
    }

    pendingResult = result

    switch authorizationStatus() {
    case .authorizedAlways, .authorizedWhenInUse:
      locationManager.requestLocation()
    case .notDetermined:
      locationManager.requestWhenInUseAuthorization()
    case .restricted, .denied:
      finishWithError(code: "PERMISSION_DENIED", message: "Location permission denied.")
    @unknown default:
      finishWithError(code: "PERMISSION_UNKNOWN", message: "Unknown authorization status.")
    }
  }

  private func authorizationStatus() -> CLAuthorizationStatus {
    if #available(iOS 14.0, *) {
      return locationManager.authorizationStatus
    }
    return CLLocationManager.authorizationStatus()
  }

  private func finishWithLocation(_ location: CLLocation) {
    pendingResult?([
      "latitude": location.coordinate.latitude,
      "longitude": location.coordinate.longitude,
    ])
    pendingResult = nil
  }

  private func finishWithError(code: String, message: String) {
    pendingResult?(FlutterError(code: code, message: message, details: nil))
    pendingResult = nil
  }

  public func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
    guard let latest = locations.last else {
      finishWithError(code: "LOCATION_UNAVAILABLE", message: "Unable to obtain location.")
      return
    }
    finishWithLocation(latest)
  }

  public func locationManager(_ manager: CLLocationManager, didFailWithError error: Error) {
    finishWithError(code: "LOCATION_ERROR", message: error.localizedDescription)
  }

  public func locationManagerDidChangeAuthorization(_ manager: CLLocationManager) {
    handleAuthorizationChange(status: manager.authorizationStatus)
  }

  public func locationManager(_ manager: CLLocationManager, didChangeAuthorization status: CLAuthorizationStatus) {
    handleAuthorizationChange(status: status)
  }

  private func handleAuthorizationChange(status: CLAuthorizationStatus) {
    guard pendingResult != nil else { return }
    switch status {
    case .authorizedAlways, .authorizedWhenInUse:
      locationManager.requestLocation()
    case .denied, .restricted:
      finishWithError(code: "PERMISSION_DENIED", message: "Location permission denied.")
    case .notDetermined:
      break
    @unknown default:
      finishWithError(code: "PERMISSION_UNKNOWN", message: "Unknown authorization status.")
    }
  }
}