// MirrorFuelProvider.swift — GitHub price-mirror provider (P0 live chain).
//
// The mirror (aptonline/fuelboard-data, pushed daily by the ingestion relay)
// is the PRODUCTION data source: its day files use the same /api/v1/stations
// envelope, so the shared decoder works verbatim. Fetching from
// raw.githubusercontent.com makes live prices work fully off-LAN — App Review
// cannot reach a private LAN relay, and consumers never have one to reach —
// with the bundled dump (app target) as the no-network last resort.
//
// Chain (LiveChainProvider) — public HTTPS only:
//   GitHub mirror → (app target: bundled dump in the ContentView catch,
//   widget: cache → placeholder)
// No local-network fallback or private IP is compiled into the app binary.

import Foundation

// MARK: - Mirror provider (GitHub raw)

/// Fetches CURRENT prices from the GitHub mirror. Same envelope as the
/// relay, so `FuelPriceProvider.decodeStations` applies unchanged.
struct MirrorFuelProvider: FuelPriceProviding {
    var baseURL = FuelHistoryStore.mirrorBase

    /// Envelope metadata from the most recent successful mirror fetch —
    /// surfaced via `LiveChainProvider.latestMeta` in Settings → About.
    static var latestMeta: RelayMeta?

    /// App-group file cache of the last fetched FULL dump, keyed by snapshot day.
    /// The mirror pushes once/day, so between pushes the app reuses the
    /// cached dump instead of re-downloading ~2.8 MB at every 12 h gate.
    static let liveDumpCacheKey = "fuelboard.liveDumpCache"
    static let liveDumpCacheFileName = "fuelboard.liveDumpCache.json"

    struct DumpCache: Codable {
        let day: String
        let data: Data
    }

    static func loadDumpCache() -> DumpCache? {
        if let raw = FuelStore.loadAppGroupFile(liveDumpCacheFileName),
           let cache = try? JSONDecoder().decode(DumpCache.self, from: raw) {
            return cache
        }

        // Migrate the legacy UserDefaults cache when present.
        guard let defaults = UserDefaults(suiteName: FuelStore.appGroupSuite),
              let raw = defaults.data(forKey: liveDumpCacheKey),
              let cache = try? JSONDecoder().decode(DumpCache.self, from: raw) else {
            return nil
        }
        if FuelStore.saveAppGroupFile(raw, name: liveDumpCacheFileName) {
            defaults.removeObject(forKey: liveDumpCacheKey)
        }
        return cache
    }

    static func saveDumpCache(day: String, data: Data) {
        guard let raw = try? JSONEncoder().encode(DumpCache(day: day, data: data)) else { return }
        _ = FuelStore.saveAppGroupFile(raw, name: liveDumpCacheFileName)
    }

    /// True when the cached dump is already the freshest the mirror has —
    /// avoids the ~2.8 MB re-download when the mirror hasn't pushed a new day.
    static func canReuseCache(cachedDay: String?, latestDay: String?) -> Bool {
        guard let cachedDay, let latestDay else { return false }
        return cachedDay == latestDay
    }

    /// Focused-path projection, replacing what the relay's radius endpoint
    /// used to do server-side: stations WITH the fuel, within radius of the
    /// point, nearest first, bounded. The alert path re-checks radius and
    /// fuel itself afterwards, so this only narrows the payload.
    static func focused(_ stations: [FuelStation], near lat: Double?, lng: Double?,
                        fuel: FuelType, radiusKM: Double?, limit: Int = 500) -> [FuelStation] {
        guard let lat, let lng, let radiusKM else { return stations }
        return Array(
            stations
                .filter { $0.prices[fuel] != nil && $0.distanceKM(to: lat, lng2: lng) <= radiusKM }
                .sorted { $0.distanceKM(to: lat, lng2: lng) < $1.distanceKM(to: lat, lng2: lng) }
                .prefix(limit)
        )
    }

    func fetchStations(near lat: Double?, lng: Double?, fuel: FuelType, radiusKM: Double?) async throws -> [FuelStation] {
        // 1. Tiny pointer fetch — the freshest snapshot day.
        guard let latest = await FuelHistoryStore.fetchLatest(base: baseURL),
              let day = latest.availableTo ?? latest.date else {
            throw FuelProviderError.mirrorUnavailable
        }
        // 2. Reuse the cached full dump when the mirror hasn't pushed a new day.
        let cache = Self.loadDumpCache()
        let data: Data
        if Self.canReuseCache(cachedDay: cache?.day, latestDay: day), let cached = cache?.data {
            data = cached
        } else {
            // Bypass the HTTP cache + short timeout: an offline refresh must
            // FAIL (→ offline banner), never re-serve a stale cached dump as
            // a "successful" live fetch.
            var req = URLRequest(url: FuelHistoryStore.historyFileURL(day: day, base: baseURL))
            req.cachePolicy = .reloadIgnoringLocalCacheData
            req.timeoutInterval = 10
            let (fetched, response) = try await URLSession.shared.data(for: req)
            guard (response as? HTTPURLResponse)?.statusCode == 200 else {
                throw FuelProviderError.mirrorUnavailable
            }
            Self.saveDumpCache(day: day, data: fetched)
            data = fetched
        }
        let stations = try FuelPriceProvider.decodeStations(from: data)
        Self.latestMeta = FuelPriceProvider.decodeRelayMeta(from: data)
        return Self.focused(stations, near: lat, lng: lng, fuel: fuel, radiusKM: radiusKM)
    }
}

// MARK: - Live chain provider

/// The live price chain — public GitHub mirror only. No private LAN fallback is
/// compiled into the app binary, so App Store/TestFlight builds cannot trigger
/// Local Network permission or leak a private IP.
struct LiveChainProvider: FuelPriceProviding {
    var mirror: FuelPriceProviding

    /// Metadata surfaced in Settings → About.
    static var latestMeta: RelayMeta?
    static var lastSource: String?

    init(mirror: FuelPriceProviding = MirrorFuelProvider()) {
        self.mirror = mirror
    }

    func fetchStations(near lat: Double?, lng: Double?, fuel: FuelType, radiusKM: Double?) async throws -> [FuelStation] {
        let stations = try await mirror.fetchStations(near: lat, lng: lng, fuel: fuel, radiusKM: radiusKM)
        Self.latestMeta = MirrorFuelProvider.latestMeta
        Self.lastSource = "github"
        return stations
    }
}