import CoreLocation

/// CoreLocation 的极简 async 封装:请求一次"使用期间"定位。
/// 无权限/拒绝/失败都返 nil,调用方用默认坐标兜底(对齐安卓首页定位失败兜底天安门)。
@MainActor
final class LocationManager: NSObject, CLLocationManagerDelegate {
    private let manager = CLLocationManager()
    private var authContinuation: CheckedContinuation<Bool, Never>?
    private var locContinuation: CheckedContinuation<CLLocationCoordinate2D?, Never>?

    override init() {
        super.init()
        manager.delegate = self
        manager.desiredAccuracy = kCLLocationAccuracyHundredMeters
    }

    /// 请求一次定位。notDetermined 先弹权限,授权后取一次坐标;拒绝/失败返 nil。
    func requestOnce() async -> CLLocationCoordinate2D? {
        // 防重入:Tab 切换会让 HomeView 的 .task 重启二次调用,避免覆盖 continuation 导致前一次永久挂起
        guard authContinuation == nil, locContinuation == nil else { return nil }
        switch manager.authorizationStatus {
        case .denied, .restricted:
            return nil
        case .notDetermined:
            guard await requestAuthorization() else { return nil }
        default:
            break
        }
        return await fetchLocation()
    }

    private func requestAuthorization() async -> Bool {
        await withCheckedContinuation { cont in
            authContinuation = cont
            manager.requestWhenInUseAuthorization()
        }
    }

    private func fetchLocation() async -> CLLocationCoordinate2D? {
        await withCheckedContinuation { cont in
            locContinuation = cont
            manager.requestLocation()
        }
    }

    // MARK: - CLLocationManagerDelegate(回调可能非主线程,跳回 MainActor;continuation 置 nil 防重复 resume)

    nonisolated func locationManagerDidChangeAuthorization(_ manager: CLLocationManager) {
        let status = manager.authorizationStatus
        Task { @MainActor in
            guard let cont = authContinuation else { return }   // init 时的初始回调:cont 还没设,忽略
            authContinuation = nil
            cont.resume(returning: status == .authorizedWhenInUse || status == .authorizedAlways)
        }
    }

    nonisolated func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        let coord = locations.first?.coordinate
        Task { @MainActor in
            guard let cont = locContinuation else { return }
            locContinuation = nil
            cont.resume(returning: coord)
        }
    }

    nonisolated func locationManager(_ manager: CLLocationManager, didFailWithError error: Error) {
        Task { @MainActor in
            guard let cont = locContinuation else { return }
            locContinuation = nil
            cont.resume(returning: nil)
        }
    }
}