import Foundation
import WatchConnectivity

extension Notification.Name {
    static let fuelBoardWatchRefreshRequested = Notification.Name("FuelBoardWatchRefreshRequested")
    static let fuelBoardShowStationDetail = Notification.Name("FuelBoardShowStationDetail")
}

@MainActor
final class WatchSyncManager: NSObject, WCSessionDelegate {
    static let shared = WatchSyncManager()

    private var pendingSnapshotPush = false

    private override init() {
        super.init()
    }

    func activate() {
        guard WCSession.isSupported() else { return }
        pendingSnapshotPush = true
        let session = WCSession.default
        if session.delegate !== self {
            session.delegate = self
        }
        session.activate()
    }

    func pushSnapshot() {
        guard WCSession.isSupported() else { return }
        let session = WCSession.default
        guard session.activationState == .activated else {
            pendingSnapshotPush = true
            return
        }
        do {
            try session.updateApplicationContext(snapshotContext())
            pendingSnapshotPush = false
        } catch {
            print("WATCH-SYNC push failed: \(error.localizedDescription)")
        }
    }

    private func snapshotContext() -> [String: Any] {
        var context: [String: Any] = [:]

        if let favourites = try? JSONEncoder().encode(FuelStore.loadFavourites()) {
            context[FuelStore.favouritesKey] = favourites
        }
        // Do NOT send the full station dump to watchOS via WatchConnectivity.
        // The UK dataset is megabytes large and exceeds application-context
        // payload limits, which prevents any snapshot from arriving. The
        // favourites payload already carries station snapshots + prices, so the
        // watch can render favourites without the full list.

        context[FuelStore.fuelKey] = FuelStore.loadSelectedFuel().rawValue
        context[FuelStore.distanceUnitKey] = FuelStore.loadDistanceUnit().rawValue
        context[FuelStore.priceDisplayStyleKey] = FuelStore.loadPriceDisplayStyle().rawValue

        if let lastRefresh = FuelStore.loadLastRefresh() {
            context[FuelStore.lastRefreshKey] = String(lastRefresh.timeIntervalSince1970)
        }

        if let handled = FuelStore.loadWatchRefreshHandled() {
            context[FuelStore.watchRefreshHandledKey] = String(handled.timeIntervalSince1970)
        }

        if let location = FuelStore.loadLocationWithDate() {
            context[FuelStore.locationKey] = "\(location.coordinate.lat),\(location.coordinate.lng),\(location.date.timeIntervalSince1970)"
        }

        return context
    }

    nonisolated func session(_ session: WCSession, activationDidCompleteWith activationState: WCSessionActivationState, error: (any Error)?) {
        if let error {
            print("WATCH-SYNC activation failed: \(error.localizedDescription)")
            return
        }
        Task { @MainActor in
            if activationState == .activated, self.pendingSnapshotPush {
                self.pushSnapshot()
            }
        }
    }

    nonisolated func sessionDidBecomeInactive(_ session: WCSession) {}

    nonisolated func sessionDidDeactivate(_ session: WCSession) {
        Task { @MainActor in
            WCSession.default.activate()
        }
    }

    nonisolated func session(_ session: WCSession, didReceiveUserInfo userInfo: [String : Any] = [:]) {
        handleIncomingMessage(userInfo)
    }

    nonisolated func session(_ session: WCSession, didReceiveMessage message: [String : Any]) {
        handleIncomingMessage(message)
    }

    private nonisolated func handleIncomingMessage(_ payload: [String: Any]) {
        if payload["fuelboard.snapshotRequest"] as? String != nil {
            Task { @MainActor in
                self.pushSnapshot()
            }
        }

        guard let raw = payload[FuelStore.watchRefreshRequestKey] as? String,
              let timestamp = TimeInterval(raw) else { return }
        let date = Date(timeIntervalSince1970: timestamp)
        Task { @MainActor in
            FuelStore.requestWatchRefresh(date)
            NotificationCenter.default.post(name: .fuelBoardWatchRefreshRequested, object: nil)
        }
    }
}