import Foundation

/// Persists the Verbinden-Tab's "known routers" list (host/username/editable name/last-connected)
/// as JSON in UserDefaults — small, structured data, no reason for its own file the way backups
/// get a directory. Passwords themselves stay exactly where they already did: the macOS Keychain
/// via `KeychainService`, keyed by "username@host", untouched by this store.
struct SavedRoutersStore {
    private static let key = "RouterOSAssistant.SavedRouters"
    private let defaults: UserDefaults

    init(defaults: UserDefaults = .standard) {
        self.defaults = defaults
    }

    /// Most recently used first.
    func load() -> [SavedRouter] {
        sortedByRecency(loadRaw())
    }

    private func loadRaw() -> [SavedRouter] {
        guard let data = defaults.data(forKey: Self.key),
              let routers = try? JSONDecoder().decode([SavedRouter].self, from: data) else { return [] }
        return routers
    }

    private func sortedByRecency(_ routers: [SavedRouter]) -> [SavedRouter] {
        routers.sorted { $0.lastConnectedAt > $1.lastConnectedAt }
    }

    /// Persists in whatever order given, then returns the recency-sorted view — every public
    /// method's return value has the same "most recently used first" order as `load()`, so a
    /// caller can always assign it straight to a displayed list without a separate re-sort.
    @discardableResult
    private func save(_ routers: [SavedRouter]) -> [SavedRouter] {
        if let data = try? JSONEncoder().encode(routers) {
            defaults.set(data, forKey: Self.key)
        }
        return sortedByRecency(routers)
    }

    /// Called after a successful connection: adds a new entry (name defaulting to `defaultName`)
    /// if this host/username/serial combination isn't known yet, or just bumps `lastConnectedAt`
    /// on the existing one. An existing entry's `name` is never touched here — that's what
    /// preserves a user's own rename across later reconnects.
    ///
    /// `serialNumber` disambiguates two physically different routers that happen to share the
    /// same host/username (e.g. both left at MikroTik's factory default 192.168.88.1/admin) —
    /// without it, connecting to a second such device would silently rename the first one's
    /// existing entry in place instead of creating a new one, live-confirmed 2026-09-16. Matching
    /// order: (1) an entry with the exact same serial wins outright; (2) failing that, exactly one
    /// same-host/username entry with no recorded serial yet is treated as the same device seen for
    /// the first time since this field existed, and gets its serial filled in now; (3) otherwise
    /// this is a genuinely new device (or an ambiguous multi-match this app won't guess at) and
    /// gets its own new entry.
    @discardableResult
    func recordSuccessfulConnection(host: String, username: String, defaultName: String, serialNumber: String? = nil) -> [SavedRouter] {
        var routers = loadRaw()
        let candidateIndices = routers.indices.filter { routers[$0].host == host && routers[$0].username == username }

        if let serialNumber, let index = candidateIndices.first(where: { routers[$0].serialNumber == serialNumber }) {
            routers[index].lastConnectedAt = Date()
            return save(routers)
        }
        let unrecordedSerialIndices = candidateIndices.filter { routers[$0].serialNumber == nil }
        if unrecordedSerialIndices.count == 1, let index = unrecordedSerialIndices.first {
            routers[index].lastConnectedAt = Date()
            routers[index].serialNumber = serialNumber
            return save(routers)
        }
        routers.append(SavedRouter(host: host, username: username, name: defaultName, serialNumber: serialNumber))
        return save(routers)
    }

    @discardableResult
    func rename(_ id: SavedRouter.ID, to newName: String) -> [SavedRouter] {
        var routers = loadRaw()
        guard let index = routers.firstIndex(where: { $0.id == id }) else { return sortedByRecency(routers) }
        routers[index].name = newName
        return save(routers)
    }

    /// Free-text location/purpose (e.g. "Keller" or "1. OG") — kept as its own method rather than
    /// folded into `rename` since a caller may want to update just one of the two, and it mirrors
    /// `rename`'s exact shape.
    @discardableResult
    func updateLocation(_ id: SavedRouter.ID, to newLocation: String) -> [SavedRouter] {
        var routers = loadRaw()
        guard let index = routers.firstIndex(where: { $0.id == id }) else { return sortedByRecency(routers) }
        routers[index].location = newLocation
        return save(routers)
    }

    @discardableResult
    func remove(_ id: SavedRouter.ID) -> [SavedRouter] {
        var routers = loadRaw()
        routers.removeAll { $0.id == id }
        return save(routers)
    }
}