import CoreLocation
import UserNotifications
import SwiftUI
import MapKit
import UIKit

/// A station the user wants to see on a map — set when a notification tap
/// can't hand off to Apple Maps (e.g. inside LiveContainer), so the app shows
/// an in-app map with directions instead.
struct StationMapRequest: Identifiable {
    let id = UUID()
    let name: String
    let latitude: Double
    let longitude: Double
}

/// Geofences favourite + closest stations and fires a local notification when
/// the user enters a station whose price is the cheapest within the radius.
///
/// Region budget: iOS allows 20 monitored regions per app — favourites are
/// always registered first, then the closest remaining stations fill the rest.
@MainActor
final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLocationManagerDelegate, UNUserNotificationCenterDelegate {
    @Published var monitoredStationIDs: [String] = []
    @Published var lastAlert: String?
    @Published private(set) var lastTestResult: String?
    @Published var pendingStationMap: StationMapRequest?

    private let manager = CLLocationManager()
    private var stations: [FuelStation] = []
    private var favourites: [FuelStation] = []
    private var fuel: FuelType = .e10
    private var radiusKM: Double = 3.0
    private var lastNotified: [String: Date] = [:]   // dedup per station
    private var enabled = false

    override init() {
        super.init()
        manager.delegate = self
        manager.desiredAccuracy = kCLLocationAccuracyHundredMeters
        manager.pausesLocationUpdatesAutomatically = true
        // Show alert banners even while the app is open, and complete the tap
        // action (opening FuelBoard) when the user taps a notification.
        UNUserNotificationCenter.current().delegate = self
        // Restore persisted state on background relaunch so region events work
        // even before the view fully appears.
        enabled = FuelStore.loadAlertsEnabled()
        fuel = FuelStore.loadAlertsFuel()
        radiusKM = FuelStore.loadAlertsRadius()
        stations = FuelStore.loadStations()
        favourites = FuelStore.loadFavourites().filter { $0.fuel == fuel }.map(\.station)
    }

    /// Re-registers geofences. Call whenever stations/favourites/settings change.
    /// Favourites are fuel-scoped entries; only entries for the monitored fuel
    /// get priority slots (a Diesel favourite must not grab a slot while
    /// monitoring Unleaded).
    func update(stations: [FuelStation], favourites: [FavouriteEntry], fuel: FuelType, radiusKM: Double) {
        // Fall back to the shared cache when called before the first fetch
        // completes (launch, background region-event wake).
        self.stations = stations.isEmpty ? FuelStore.loadStations() : stations
        self.favourites = favourites.isEmpty
            ? FuelStore.loadFavourites().filter { $0.fuel == fuel }.map(\.station)
            : favourites.filter { $0.fuel == fuel }.map(\.station)
        self.fuel = fuel
        self.radiusKM = radiusKM

        for region in manager.monitoredRegions {
            manager.stopMonitoring(for: region)
        }
        monitoredStationIDs = []

        guard enabled else { return }

        // Favourites first (guaranteed slots), then closest stations, max 18.
        // `self.favourites` is already filtered to the monitored fuel.
        var candidates: [FuelStation] = self.favourites
        let favIDs = Set(self.favourites.map(\.id))
        let location = FuelStore.loadLocation()
        let others = stations
            .filter { !favIDs.contains($0.id) }
            .sorted { lhs, rhs in
                guard let location else { return false }
                return lhs.distanceKM(to: location.lat, lng2: location.lng) <
                       rhs.distanceKM(to: location.lat, lng2: location.lng)
            }
        candidates.append(contentsOf: others)

        var registered: [String] = []
        for station in candidates.prefix(18) where station.prices[fuel] != nil {
            let region = CLCircularRegion(
                center: CLLocationCoordinate2D(latitude: station.lat, longitude: station.lng),
                radius: 300,
                identifier: station.id
            )
            region.notifyOnEntry = true
            region.notifyOnExit = false
            manager.startMonitoring(for: region)
            registered.append(station.id)
        }
        monitoredStationIDs = registered
    }

    func setEnabled(_ enabled: Bool) {
        self.enabled = enabled
        if !enabled {
            for region in manager.monitoredRegions {
                manager.stopMonitoring(for: region)
            }
            monitoredStationIDs = []
        } else {
            requestPermissions()
            // Re-register geofences from restored cache immediately.
            update(stations: stations, favourites: FuelStore.loadFavourites(), fuel: fuel, radiusKM: radiusKM)
        }
    }

    var isEnabled: Bool { enabled }

    private func requestPermissions() {
        // Region monitoring needs Always location for background delivery.
        switch manager.authorizationStatus {
        case .notDetermined:
            manager.requestWhenInUseAuthorization()
            manager.requestAlwaysAuthorization()
        case .authorizedWhenInUse:
            manager.requestAlwaysAuthorization()
        default:
            break
        }
        UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) { _, _ in }
    }

    // MARK: - Region events

    nonisolated func locationManager(_ manager: CLLocationManager, didEnterRegion region: CLRegion) {
        Task { @MainActor in
            self.handleEntry(region)
        }
    }

    nonisolated func locationManager(_ manager: CLLocationManager, didFailWithError error: Error) {
        // Ignore — alerts still work while the app is open.
    }

    private func handleEntry(_ region: CLRegion) {
        let stationID = region.identifier
        // Fall back to cached data on background wake (stations may not be
        // fetched yet when the app is relaunched by a region event).
        if stations.isEmpty { stations = FuelStore.loadStations() }
        guard let station = stations.first(where: { $0.id == stationID }) else { return }

        // Dedup: one alert per station per hour.
        if let last = lastNotified[stationID], Date().timeIntervalSince(last) < 3600 { return }

        Task {
            do {
                // Fresh prices around the entered station (alert radius in km).
                let fresh = try await FuelPriceProvider.active.fetchStations(
                    near: station.lat, lng: station.lng, fuel: fuel,
                    radiusKM: max(radiusKM, 10)  // fetch wider than trigger radius
                )
                let withinRadius = fresh.filter {
                    $0.prices[fuel] != nil &&
                    $0.distanceKM(to: station.lat, lng2: station.lng) <= radiusKM
                }
                guard let cheapest = withinRadius.min(by: { $0.prices[fuel]! < $1.prices[fuel]! }),
                      cheapest.id == station.id,
                      let price = cheapest.prices[fuel] else { return }

                fireAlert(for: cheapest, price: price)
                lastNotified[stationID] = Date()
            } catch {
                // Silent — geofence state stays valid for next entry.
            }
        }
    }

    private func fireAlert(for station: FuelStation, price: Double) {
        let brand = station.brand.isEmpty ? station.name : station.brand
        let unit = FuelStore.loadDistanceUnit()
        let distanceText: String = {
            guard let location = FuelStore.loadLocation() else { return unit.format(0) }
            return unit.format(station.distanceKM(to: location.lat, lng2: location.lng))
        }()
        let content = UNMutableNotificationContent()
        content.title = "Cheapest \(fuel.displayName) nearby: \(brand)"
        content.body = "\(station.name) · \(distanceText) away · \(String(format: "%.1fp", price)). Tap for directions."
        content.sound = .default
        addAlertRequest(content: content, station: station)
        lastAlert = "\(brand) · \(String(format: "%.1fp", price)) · \(distanceText) away"
    }

    /// Adds a notification whose tap opens directions to `station`. The
    /// station's coordinates ride in `userInfo` so the tap handler can route
    /// to Apple Maps (or an in-app fallback), and a map snapshot with a pin is
    /// attached so the expanded notification shows where the station is.
    /// `mapStatus` reports whether the snapshot attached (or why not), so the
    /// test UI can show it instead of failing silently.
    private func addAlertRequest(
        content: UNMutableNotificationContent,
        station: FuelStation,
        mapStatus: ((String) -> Void)? = nil
    ) {
        content.userInfo = [
            "stationName": station.name,
            "stationLat": station.lat,
            "stationLng": station.lng,
        ]
        let options = MKMapSnapshotter.Options()
        options.region = MKCoordinateRegion(
            center: CLLocationCoordinate2D(latitude: station.lat, longitude: station.lng),
            span: MKCoordinateSpan(latitudeDelta: 0.02, longitudeDelta: 0.02)
        )
        options.size = CGSize(width: 800, height: 400)
        options.mapType = .standard
        let snapshotter = MKMapSnapshotter(options: options)
        snapshotter.start { [content] snapshot, error in
            Task { @MainActor in
                let finalContent = content
                var status = "map: no image"
                if let snapshot, error == nil,
                   let image = Self.mapImage(snapshot: snapshot, station: station) {
                    let url = FileManager.default.temporaryDirectory
                        .appendingPathComponent("alert-map-\(UUID().uuidString).png")
                    if let data = image.pngData(), (try? data.write(to: url)) != nil,
                       let attachment = try? UNNotificationAttachment(identifier: "map", url: url, options: nil) {
                        finalContent.attachments = [attachment]
                        status = "map: attached"
                    }
                } else if let error {
                    status = "map: snapshot failed (\(error.localizedDescription))"
                }
                mapStatus?(status)
                let request = UNNotificationRequest(identifier: UUID().uuidString, content: finalContent, trigger: nil)
                UNUserNotificationCenter.current().add(request)
            }
        }
    }

    /// Draws a red pin on the map snapshot at the station's location.
    private static func mapImage(snapshot: MKMapSnapshotter.Snapshot, station: FuelStation) -> UIImage? {
        let image = snapshot.image
        let point = snapshot.point(for: CLLocationCoordinate2D(latitude: station.lat, longitude: station.lng))
        let renderer = UIGraphicsImageRenderer(size: image.size)
        return renderer.image { context in
            image.draw(at: .zero)
            let pinSize = CGSize(width: 36, height: 36)
            let pinRect = CGRect(x: point.x - pinSize.width / 2, y: point.y - pinSize.height, width: pinSize.width, height: pinSize.height)
            let pin = UIImage(systemName: "mappin.circle.fill")?
                .withTintColor(.systemRed, renderingMode: .alwaysTemplate)
            pin?.draw(in: pinRect)
        }
    }

    /// Fires a test alert built from REAL data: the cheapest station selling
    /// the monitored fuel within the configured alert radius of the current
    /// location — the same criteria a live geofence entry would apply, minus
    /// the geofence itself. Uses the monitor's live state (fuel, radius,
    /// stations) so the notification reflects the Alerts-tab configuration.
    func sendTestNotification() {
        let unit = FuelStore.loadDistanceUnit()
        let location = FuelStore.loadLocation()
        let sellers = stations.filter { $0.prices[fuel] != nil }

        // Cheapest within radius, judged around the current location —
        // identical to handleEntry's withinRadius logic.
        let inRadius = sellers.filter { station in
            guard let location else { return true }
            return station.distanceKM(to: location.lat, lng2: location.lng) <= radiusKM
        }
        let candidate = inRadius.min { ($0.prices[fuel] ?? .infinity) < ($1.prices[fuel] ?? .infinity) }

        if let candidate, let price = candidate.prices[fuel] {
            let brand = candidate.brand.isEmpty ? candidate.name : candidate.brand
            let distanceText: String = {
                guard let location else { return unit.format(0) }
                return unit.format(candidate.distanceKM(to: location.lat, lng2: location.lng))
            }()
            let content = UNMutableNotificationContent()
            content.title = "Cheapest \(fuel.displayName) nearby: \(brand)"
            content.body = "\(candidate.name) · \(distanceText) away · \(String(format: "%.1fp", price)). Tap for directions."
            content.sound = .default
            let baseResult = "\(fuel.displayName) · \(brand) · \(String(format: "%.1fp", price)) · \(distanceText) away · radius \(unit.format(radiusKM))"
            addAlertRequest(content: content, station: candidate) { status in
                self.lastTestResult = "\(baseResult) · \(status)"
            }
            lastTestResult = baseResult
        } else {
            // No real candidate (no stations loaded yet, or none sell the
            // monitored fuel) — still fire so delivery is testable, but say
            // why the real criteria found nothing.
            let content = UNMutableNotificationContent()
            content.title = "FuelBoard test alert"
            content.body = sellers.isEmpty
                ? "No station data loaded yet — open the Stations tab first, then retry."
                : "No \(fuel.displayName.lowercased()) station within \(unit.format(radiusKM)) of you."
            content.sound = .default
            let request = UNNotificationRequest(identifier: UUID().uuidString, content: content, trigger: nil)
            UNUserNotificationCenter.current().add(request)
            lastTestResult = sellers.isEmpty
                ? "No stations loaded — open the Stations tab first"
                : "No \(fuel.displayName.lowercased()) seller within \(unit.format(radiusKM))"
        }
    }

    /// Fires a notification with NO criteria checks at all — no geofence, no
    /// cheapest-within-radius, no dedup, no permission gate, no fuel/radius
    /// coupling. Still carries a REAL station (the nearest one selling the
    /// monitored fuel) with its real name, price, distance and coordinates, so
    /// the tap action — directions to that station — is testable regardless of
    /// every alert condition. If notifications are denied system-wide nothing
    /// can display, but this fires regardless of every FuelBoard condition.
    func sendPlainTestNotification() {
        let unit = FuelStore.loadDistanceUnit()
        let location = FuelStore.loadLocation()
        let sellers = stations.filter { $0.prices[fuel] != nil }
        let nearest = sellers.min { lhs, rhs in
            let ld = location.map { lhs.distanceKM(to: $0.lat, lng2: $0.lng) } ?? 0
            let rd = location.map { rhs.distanceKM(to: $0.lat, lng2: $0.lng) } ?? 0
            return ld < rd
        }

        let content = UNMutableNotificationContent()
        if let nearest, let price = nearest.prices[fuel] {
            let brand = nearest.brand.isEmpty ? nearest.name : nearest.brand
            let distanceText: String = {
                guard let location else { return unit.format(0) }
                return unit.format(nearest.distanceKM(to: location.lat, lng2: location.lng))
            }()
            content.title = "\(brand) — plain test notification"
            content.body = "\(nearest.name) · \(distanceText) away · \(String(format: "%.1fp", price)). Tap for directions."
            content.sound = .default
            addAlertRequest(content: content, station: nearest)
        } else {
            content.title = "FuelBoard test notification"
            content.body = "No station data loaded yet — open the Stations tab first."
            content.sound = .default
            let request = UNNotificationRequest(identifier: UUID().uuidString, content: content, trigger: nil)
            UNUserNotificationCenter.current().add(request)
        }
    }

    // MARK: - Notification presentation + tap

    /// Show alert banners even while FuelBoard is in the foreground — without
    /// this, the system silently suppresses notifications when the app is open.
    nonisolated func userNotificationCenter(
        _ center: UNUserNotificationCenter,
        willPresent notification: UNNotification,
        withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void
    ) {
        Task { @MainActor in
            completionHandler([.banner, .sound])
        }
    }

    /// Tapping a notification opens Apple Maps directions to the station from
    /// the user's current location. If Apple Maps can't be opened (e.g. inside
    /// LiveContainer), an in-app map sheet with directions is shown instead.
    nonisolated func userNotificationCenter(
        _ center: UNUserNotificationCenter,
        didReceive response: UNNotificationResponse,
        withCompletionHandler completionHandler: @escaping () -> Void
    ) {
        let userInfo = response.notification.request.content.userInfo
        let name = userInfo["stationName"] as? String
        let lat = userInfo["stationLat"] as? Double
        let lng = userInfo["stationLng"] as? Double
        Task { @MainActor in
            if let name, let lat, let lng {
                openDirections(to: name, latitude: lat, longitude: lng)
            }
        }
        completionHandler()
    }

    /// Opens Apple Maps with driving directions to the station; falls back to
    /// the in-app map sheet when the hand-off fails.
    @MainActor
    private func openDirections(to name: String, latitude: Double, longitude: Double) {
        let query = name.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed) ?? ""
        guard let url = URL(string: "maps://?daddr=\(latitude),\(longitude)&q=\(query)") else {
            pendingStationMap = StationMapRequest(name: name, latitude: latitude, longitude: longitude)
            return
        }
        UIApplication.shared.open(url) { opened in
            Task { @MainActor in
                if !opened {
                    self.pendingStationMap = StationMapRequest(name: name, latitude: latitude, longitude: longitude)
                }
            }
        }
    }
}