// LiveActivityManager.swift — app-side driver for the FuelBoard Live Activity.
//
// The app owns the activity lifecycle (request / update / end) because the
// activity's own sandbox cannot fetch prices or read location. It mirrors the
// app's TOP badge exactly: cheapest station selling the SELECTED fuel within
// the CHOSEN distance radius. Call sites:
//   - every location fix (foreground AND background significant-change wake-ups)
//   - after every station refresh
//   - when the Settings toggle flips
//
// Live Activities auto-end after 8 h — this manager re-requests a fresh one
// just before the cap so a long drive keeps its glanceable pill.

import ActivityKit
import Foundation

@MainActor
enum LiveActivityManager {
    /// The running activity, if any.
    private static var current: Activity<FuelBoardLiveActivityAttributes>?
    /// When `current` was requested. This SDK's `Activity` no longer exposes
    /// `startDate`, so the manager tracks it locally to honour the 8 h cap.
    private static var currentStartDate: Date?

    /// The system ends Live Activities after 8 hours. Restart at 7h59m so the
    /// pill never silently disappears mid-drive.
    private static let restartThreshold: TimeInterval = 7 * 3600 + 59 * 60

    /// Recomputes the cheapest-in-radius station and updates the activity.
    /// Passing `enabled: false` (or no usable data) ends any running activity.
    /// `priceDisplayStyle` overrides the saved style (used when the setting
    /// just changed and the save may not have landed yet); nil = read storage.
    static func update(
        stations: [FuelStation],
        fuel: FuelType,
        radiusKM: Double,
        location: Coordinate?,
        enabled: Bool,
        priceDisplayStyle: PriceDisplayStyle? = nil
    ) {
        guard enabled, let location else {
            end()
            return
        }
        guard let best = cheapestStation(
            stations: stations, fuel: fuel, radiusKM: radiusKM,
            lat: location.lat, lng: location.lng
        ), let price = best.prices[fuel] else {
            end()
            return
        }

        let state = FuelBoardLiveActivityAttributes.ContentState(
            fuel: fuel,
            stationID: best.id,
            stationName: best.name,
            brand: best.brand,
            pricePence: price,
            priceDisplayStyle: priceDisplayStyle ?? FuelStore.loadPriceDisplayStyle(),
            distanceKM: FuelStore.displayDistanceKM(station: best, userLat: location.lat, userLng: location.lng),
            lat: best.lat,
            lng: best.lng,
            updatedAt: Date()
        )
        let attributes = FuelBoardLiveActivityAttributes()

        if let current {
            // Near the 8 h cap? End and re-request so the pill keeps living.
            let age = currentStartDate.map { Date().timeIntervalSince($0) } ?? 0
            if age >= restartThreshold {
                Task { await current.end(nil, dismissalPolicy: .immediate) }
                self.current = nil
                currentStartDate = nil
                start(attributes: attributes, state: state)
            } else {
                Task { await current.update(using: state) }
            }
        } else {
            start(attributes: attributes, state: state)
        }
    }

    /// Ends any running activity (toggle off / app reset).
    static func end() {
        guard let current else { return }
        Task { await current.end(nil, dismissalPolicy: .immediate) }
        self.current = nil
        currentStartDate = nil
    }

    // MARK: - Internals

    private static func start(
        attributes: FuelBoardLiveActivityAttributes,
        state: FuelBoardLiveActivityAttributes.ContentState
    ) {
        do {
            current = try Activity.request(
                attributes: attributes,
                content: .init(state: state, staleDate: nil),
                pushType: nil
            )
            currentStartDate = Date()
        } catch {
            // User disabled Live Activities in Settings, or system budget —
            // silent: the feature just doesn't appear.
            current = nil
            currentStartDate = nil
        }
    }

    /// Cheapest station selling `fuel` within `radiusKM` of the location —
    /// identical semantics to the app list's TOP badge (price first, then
    /// distance as the tie-breaker).
    static func cheapestStation(
        stations: [FuelStation],
        fuel: FuelType,
        radiusKM: Double,
        lat: Double,
        lng: Double
    ) -> FuelStation? {
        stations
            .filter { $0.prices[fuel] != nil }
            .filter { $0.distanceKM(to: lat, lng2: lng) <= radiusKM }
            .min { lhs, rhs in
                let lPrice = lhs.prices[fuel]!
                let rPrice = rhs.prices[fuel]!
                if lPrice != rPrice { return lPrice < rPrice }
                return lhs.distanceKM(to: lat, lng2: lng) < rhs.distanceKM(to: lat, lng2: lng)
            }
    }
}