import Foundation
import OSLog
import CoreLocation
import WeatherKit

private let log = Logger(subsystem: "com.scarriffleservices.onyx", category: "Weather")

/// Liefert den aktuellen Standort, oder sagt warum nicht.
///
/// Eigene Klasse statt eines Aufrufs mittendrin: `CLLocationManager` meldet
/// asynchron über einen Delegaten, und die Berechtigung kann sich jederzeit
/// ändern. Beides gehört an eine Stelle.
@MainActor
final class LocationProvider: NSObject, CLLocationManagerDelegate {

    private let manager = CLLocationManager()
    private var pending: [CheckedContinuation<CLLocation?, Never>] = []

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

    var authorization: CLAuthorizationStatus { manager.authorizationStatus }

    var isDenied: Bool {
        authorization == .denied || authorization == .restricted
    }

    func requestAuthorization() {
        guard authorization == .notDetermined else { return }
        manager.requestWhenInUseAuthorization()
    }

    /// Eine einzelne Ortung. Liefert `nil`, wenn keine Berechtigung vorliegt
    /// oder nichts hereinkommt.
    func currentLocation() async -> CLLocation? {
        guard !isDenied else { return nil }
        if authorization == .notDetermined {
            requestAuthorization()
            // Auf die Entscheidung des Nutzers warten hieße, hier zu blockieren.
            // Beim nächsten Durchlauf steht sie fest.
            return nil
        }
        if let cached = manager.location, cached.timestamp.timeIntervalSinceNow > -900 {
            return cached
        }
        return await withCheckedContinuation { continuation in
            pending.append(continuation)
            manager.requestLocation()
        }
    }

    private func resume(with location: CLLocation?) {
        let waiting = pending
        pending.removeAll()
        waiting.forEach { $0.resume(returning: location) }
    }

    nonisolated func locationManager(_ manager: CLLocationManager,
                                     didUpdateLocations locations: [CLLocation]) {
        Task { @MainActor in self.resume(with: locations.last) }
    }

    nonisolated func locationManager(_ manager: CLLocationManager,
                                     didFailWithError error: Error) {
        Task { @MainActor in
            log.error("Ortung fehlgeschlagen: \(error.localizedDescription, privacy: .public)")
            self.resume(with: nil)
        }
    }
}

/// Wetter aus Apples WeatherKit.
@MainActor
public final class WeatherKitSource {

    private let service = WeatherService.shared
    private let location = LocationProvider()
    private let geocoder = CLGeocoder()

    public init() {}

    public var locationIsDenied: Bool { location.isDenied }
    public func requestLocationAuthorization() { location.requestAuthorization() }

    public func load(_ place: WeatherPlace) async -> WeatherState {
        let coordinate: CLLocation
        let placeName: String

        switch place {
        case .current:
            guard let here = await location.currentLocation() else {
                return location.isDenied
                    ? .locationDenied
                    : .unavailable(lastKnown: nil, reason: "Standort nicht verfügbar")
            }
            coordinate = here
            placeName = await name(for: here)

        case .fixed(let name, let latitude, let longitude):
            coordinate = CLLocation(latitude: latitude, longitude: longitude)
            placeName = name
        }

        do {
            let weather = try await service.weather(for: coordinate)
            return .ready(Self.snapshot(from: weather,
                                        placeName: placeName,
                                        attribution: try? await attribution()))
        } catch {
            log.error("WeatherKit: \(error.localizedDescription, privacy: .public)")
            return .unavailable(lastKnown: nil, reason: error.localizedDescription)
        }
    }

    /// Apples Namensnennung. Keine Kür — sie ist Bedingung der Nutzung.
    private func attribution() async throws -> WeatherAttribution {
        let legal = try await service.attribution
        return WeatherAttribution(name: "Apple Weather",
                                  legalPageURL: legal.legalPageURL,
                                  logoURL: legal.combinedMarkDarkURL)
    }

    private func name(for location: CLLocation) async -> String {
        guard let placemark = try? await geocoder.reverseGeocodeLocation(location).first else {
            return "Aktueller Ort"
        }
        return placemark.locality ?? placemark.subAdministrativeArea
            ?? placemark.administrativeArea ?? "Aktueller Ort"
    }

    // MARK: - Umwandlung

    private static func snapshot(from weather: Weather,
                                 placeName: String,
                                 attribution: WeatherAttribution?) -> WeatherSnapshot {
        let current = weather.currentWeather
        let today = weather.dailyForecast.first

        return WeatherSnapshot(
            placeName: placeName,
            temperature: current.temperature,
            apparentTemperature: current.apparentTemperature,
            condition: map(current.condition),
            isDaylight: current.isDaylight,
            humidity: current.humidity,
            windSpeed: current.wind.speed,
            high: today?.highTemperature,
            low: today?.lowTemperature,
            hourly: weather.hourlyForecast.forecast
                .filter { $0.date >= Date() }
                .prefix(12)
                .map {
                    HourlyPoint(date: $0.date,
                                temperature: $0.temperature,
                                condition: map($0.condition),
                                precipitationChance: $0.precipitationChance)
                },
            asOf: current.date,
            attribution: attribution)
    }

    /// WeatherKit kennt deutlich mehr Lagen als hier unterschieden werden.
    /// Feiner aufzulösen bringt nichts: das Widget hat ein Symbol und ein Wort
    /// Platz, und „mäßiger Sprühregen" liest dort niemand.
    private static func map(_ condition: WeatherKit.WeatherCondition) -> WeatherCondition {
        switch condition {
        case .clear: .clear
        case .mostlyClear: .mostlyClear
        case .partlyCloudy, .mostlyCloudy: .partlyCloudy
        case .cloudy: .cloudy
        case .foggy, .haze, .smoky: .fog
        case .drizzle, .freezingDrizzle: .drizzle
        case .rain, .sunShowers, .freezingRain: .rain
        case .heavyRain: .heavyRain
        case .sleet, .wintryMix, .hail: .sleet
        case .snow, .flurries, .sunFlurries, .blowingSnow: .snow
        case .heavySnow, .blizzard: .heavySnow
        case .thunderstorms, .isolatedThunderstorms, .scatteredThunderstorms,
             .strongStorms, .tropicalStorm, .hurricane: .thunderstorm
        case .windy, .breezy, .blowingDust: .windy
        case .hot: .hot
        case .frigid: .frigid
        @unknown default: .unknown
        }
    }
}