import Foundation

actor SDLSuperService {
    typealias MessageHandler = @Sendable (SDLSuperMessage) async -> Void

    private let serverEndpoint: SDLConfiguration.ResolvedServerEndpoint
    private let port: UInt16

    private var onMessage: MessageHandler = { _ in }
    private var currentSession: SDLSuperSession?
    private var generation: UInt64 = 0
    private var isRunning = false
    private var isStopping = false
    private var needsImmediateRestart = false
    private let retryDelay: Duration

    init(serverEndpoint: SDLConfiguration.ResolvedServerEndpoint, port: UInt16 = 1443, retryDelay: Duration = .seconds(5)) {
        self.serverEndpoint = serverEndpoint
        self.port = port
        self.retryDelay = retryDelay
    }

    func updateMessageHandler(_ onMessage: @escaping MessageHandler) {
        self.onMessage = onMessage
    }

    func run() async throws {
        guard !self.isRunning else {
            return
        }

        self.isRunning = true
        self.isStopping = false

        defer {
            self.isRunning = false
            self.currentSession = nil
        }

        while !Task.isCancelled, !self.isStopping {
            let generation = self.nextGeneration()
            let session = SDLSuperSession(
                serverEndpoint: self.serverEndpoint,
                port: self.port,
                onMessage: { [weak self] message in
                    await self?.handleMessage(message, generation: generation)
                }
            )

            self.currentSession = session

            do {
                try await session.run()
                self.clearCurrent(session, generation: generation)
                await session.stop()
                SDLLogger.log("[SDLSuperService] session ended, will restart", category: .super)
            } catch is CancellationError {
                self.clearCurrent(session, generation: generation)
                await session.stop()
                throw CancellationError()
            } catch {
                self.clearCurrent(session, generation: generation)
                await session.stop()

                guard !self.isStopping else {
                    break
                }

                SDLLogger.log("[SDLSuperService] session failed: \(error.localizedDescription), will restart", category: .super)
            }

            if self.consumeImmediateRestartRequest() {
                SDLLogger.log("[SDLSuperService] session invalidated after wakeup, will restart immediately", category: .super)
                continue
            }

            try await Task.sleep(for: self.retryDelay)
        }
    }

    func stop() async {
        self.isStopping = true
        await self.invalidateCurrentSession()
    }

    func recoverAfterWake() async {
        guard !self.isStopping else {
            return
        }

        self.needsImmediateRestart = true
        await self.invalidateCurrentSession()
    }

    func send(type: SDLPacketType, data: Data) async {
        await self.currentSession?.send(type: type, data: data)
    }

    private func nextGeneration() -> UInt64 {
        self.generation &+= 1
        return self.generation
    }

    private func invalidateCurrentSession() async {
        self.generation &+= 1

        let session = self.currentSession
        self.currentSession = nil

        await session?.stop()
    }

    private func consumeImmediateRestartRequest() -> Bool {
        let needsImmediateRestart = self.needsImmediateRestart
        self.needsImmediateRestart = false
        return needsImmediateRestart
    }

    private func clearCurrent(_ session: SDLSuperSession, generation: UInt64) {
        guard self.generation == generation else {
            return
        }

        if self.currentSession === session {
            self.currentSession = nil
        }
    }

    private func handleMessage(_ message: SDLSuperMessage, generation: UInt64) async {
        guard self.generation == generation else {
            return
        }

        await self.onMessage(message)
    }
}