import Foundation

/// Pure, testable logic behind the Siri "cheapest fuel near me" intent.
/// Foundation-only on purpose: `Shared/` joins both the app and widget
/// targets, and FuelBoardTests exercises this directly.
enum SiriCheapestLookup {

    /// The cheapest station selling `fuel` WITHIN `withinMiles` of the given
    /// point, tie-broken by distance. Stations without a price for `fuel`, or
    /// farther than the radius, are skipped entirely. Returns nil when no
    /// station sells the fuel inside the radius.
    ///
    /// Radius scoping mirrors the app's Stations tab (search radius
    /// 5/10/15 mi): without it, "cheapest near me" silently answers the
    /// UK-wide minimum — a genuinely cheap station hundreds of miles away
    /// (found with real data: GULF HISTON 100.9p was 132 mi from the phone).
    static func cheapest(
        in stations: [FuelStation],
        fuel: FuelType,
        fromLat lat: Double,
        lng: Double,
        withinMiles: Double
    ) -> FuelStation? {
        let radiusKM = withinMiles * 1.60934
        return stations
            .filter { $0.prices[fuel] != nil && $0.distanceKM(to: lat, lng2: lng) <= radiusKM }
            .min { lhs, rhs in
                guard let lp = lhs.prices[fuel], let rp = rhs.prices[fuel] else {
                    return false
                }
                if lp != rp { return lp < rp }
                return lhs.distanceKM(to: lat, lng2: lng) < rhs.distanceKM(to: lat, lng2: lng)
            }
    }

    /// A short freshness stamp for the dialog: "as of 6:30 AM".
    /// Prefers the GOV.UK `data_updated` stamp carried by the relay (ISO 8601
    /// with or without fractional seconds); falls back to the local
    /// last-refresh date; returns "" when there is no data at all.
    static func freshnessLabel(updated: String?, lastRefresh: Date?, now: Date = Date()) -> String {
        let date: Date?
        if let updated {
            date = Self.parseISO(updated) ?? lastRefresh
        } else {
            date = lastRefresh
        }
        guard let date else { return "" }
        let formatter = DateFormatter()
        formatter.dateFormat = "h:mm a"
        formatter.locale = Locale(identifier: "en_GB")
        return "as of \(formatter.string(from: date))"
    }

    private static func parseISO(_ string: String) -> Date? {
        let withFraction = ISO8601DateFormatter()
        withFraction.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
        if let date = withFraction.date(from: string) { return date }
        let plain = ISO8601DateFormatter()
        plain.formatOptions = [.withInternetDateTime]
        return plain.date(from: string)
    }

    /// The user's TOP favourite for `fuel`: the first entry in the manual
    /// favourites order (the Favourites tab's drag-and-drop order IS the
    /// widget/priority order — the first station of a fuel is its "single
    /// widget" favourite). Favourites are refreshed against the current
    /// station dump first so prices are as fresh as the cache allows;
    /// stations missing from the dump keep their cached snapshot, so the
    /// answer still works fully offline. Returns nil when the user has no
    /// favourite for that fuel.
    static func topFavourite(
        in favourites: [FavouriteEntry],
        from stations: [FuelStation],
        fuel: FuelType
    ) -> FavouriteEntry? {
        let refreshed = FuelStore.refreshedFavourites(favourites, from: stations)
        return refreshed.first { $0.fuel == fuel }
    }

    /// Apple Maps URL for turn-by-turn directions to a point. MUST be the
    /// universal-link form (https://maps.apple.com) — OpenURLIntent rejects
    /// custom schemes like `maps://`, and the https form survives copy/paste
    /// and the share sheet.
    static func mapsURL(latitude: Double, longitude: Double) -> URL {
        URL(string: "https://maps.apple.com/?daddr=\(latitude),\(longitude)")!
    }
}