import Foundation
import GhosttyTerminal
import TXCore
import TXTransport
import TsnetBridge

enum TsnetError: Error { case newNodeFailed, notUp }

/// 主 tsnet 节点管理器（线程安全，供 SSHTerminalModel 在后台线程 up/dial）。
/// up 后节点常驻，重连时复用（只重新 dial fd，不重新加入 tailnet）。
final class TsnetManager: @unchecked Sendable {
    private let lock = NSLock()
    private var node: TsnetbridgeNode?
    private let stateDir: String

    init() {
        let base = NSSearchPathForDirectoriesInDomains(.applicationSupportDirectory, .userDomainMask, true)[0]
        stateDir = base + "/tsnet-main"
        try? FileManager.default.createDirectory(atPath: stateDir, withIntermediateDirectories: true)
    }

    /// 确保节点已 up（幂等）。阻塞，需后台线程调用。
    func ensureUp(authKey: String, timeoutMs: Int) throws {
        lock.lock(); let existing = node; lock.unlock()
        if existing != nil { return }
        guard let n = TsnetbridgeNewNode(stateDir, "terminalx-ipad") else { throw TsnetError.newNodeFailed }
        try n.up(withAuthKey: authKey, timeoutMs: timeoutMs)
        lock.lock(); node = n; lock.unlock()
    }

    /// 经 tsnet dial tailnet 内 host:port，返回已连接 fd。阻塞，需后台线程调用。
    /// 带重试：tsnet 刚 Up 后到 peer 的路径（DERP/直连打洞）预热期间首次 dial 可能 i/o timeout，
    /// 短退避重试若干次直到路径就绪。
    func dialFD(host: String, port: Int, timeoutMs: Int) throws -> Int32 {
        lock.lock(); let n = node; lock.unlock()
        guard let n else { throw TsnetError.notUp }
        var lastError: Error?
        for attempt in 0 ..< 6 {
            do {
                var fd: Int64 = -1
                try n.dialTCPFD(host, port: port, timeoutMs: 8000, ret0_: &fd)
                return Int32(fd)
            } catch {
                lastError = error
                if attempt < 5 { Thread.sleep(forTimeInterval: 2.0) }  // 后台线程，路径预热
            }
        }
        throw lastError ?? TsnetError.notUp
    }
}

/// 线程安全地持有 transport 引用，供 libghostty 的输入/resize 回调（非主线程）安全取用。
final class TransportHolder: @unchecked Sendable {
    private let lock = NSLock()
    private var value: Transport?
    var transport: Transport? {
        get { lock.lock(); defer { lock.unlock() }; return value }
        set { lock.lock(); value = newValue; lock.unlock() }
    }
}

/// 输出闸门：surface 未 attach 时 receive 会丢弃写入，故未就绪先缓冲、就绪后按序 flush（修白屏）。
final class OutputGate: @unchecked Sendable {
    private let lock = NSLock()
    private let session: InMemoryTerminalSession
    private var ready = false
    private var pending = Data()

    init(session: InMemoryTerminalSession) { self.session = session }

    func deliver(_ data: Data) {
        lock.lock()
        if ready { lock.unlock(); session.receive(data) }
        else { pending.append(data); lock.unlock() }
    }

    func markReady() {
        lock.lock()
        if ready { lock.unlock(); return }
        ready = true
        let buffered = pending; pending = Data()
        lock.unlock()
        if !buffered.isEmpty { session.receive(buffered) }
    }
}

/// M0 SSH 终端会话模型：SSHSession(libssh2) ⇄ GhosttyKit in-memory 终端，
/// 由 TXCore.SessionMachine 编排生命周期（断线指数退避自动重连、后台冻结/前台恢复）。
@MainActor
final class SSHTerminalModel: ObservableObject {
    let state: TerminalViewState
    let session: InMemoryTerminalSession
    private let holder: TransportHolder
    private let gate: OutputGate

    /// 是否展示终端页（连接后保持，重连/后台期间不退回表单）。
    @Published var showsTerminal = false
    @Published var banner: String = ""
    @Published var phaseText: String = "空闲"
    /// 非 nil 时进入 tmux control-mode（原生 tab）。
    @Published var tmuxController: TmuxController?

    private var machine = SessionMachine()
    private var config: SSHConfig?
    private var reconnectTask: Task<Void, Never>?
    private var autoCommand: String?

    /// tsnet 模式：非 nil 时经 tsnet fd 桥连接（而非系统直连），重连复用同一节点。
    private var tsnetAuthKey: String?
    private let tsnetMgr = TsnetManager()

    init() {
        let holder = TransportHolder()
        let session = InMemoryTerminalSession(
            write: { data in holder.transport?.send(data) },
            resize: { vp in holder.transport?.resize(cols: vp.columns, rows: vp.rows) }
        )
        let state = TerminalViewState()
        state.configuration = TerminalSurfaceOptions(backend: .inMemory(session))
        self.holder = holder
        self.session = session
        self.state = state
        self.gate = OutputGate(session: session)
    }

    // MARK: - 公开入口

    func connect(host: String, port: Int, username: String, password: String) {
        config = SSHConfig(host: host, port: port, username: username,
                           authentication: .password(password))
        run(machine.reduce(.connectRequested))
    }

    func close() { run(machine.reduce(.closeRequested)) }
    func enterBackground() { run(machine.reduce(.enteredBackground)) }
    func enterForeground() { run(machine.reduce(.enteredForeground)) }

    /// TerminalScreen 在 surface 首次布局后调用：放行缓冲输出（+ 无头自动命令）。
    func markSurfaceReady() {
        gate.markReady()
        if let cmd = autoCommand {
            autoCommand = nil
            let holder = self.holder
            Task {
                try? await Task.sleep(nanoseconds: 2_500_000_000)
                holder.transport?.send(Data("\n".utf8))
                try? await Task.sleep(nanoseconds: 900_000_000)
                holder.transport?.send(Data((cmd + "\n").utf8))
            }
        }
    }

    /// 无头验证：从启动参数自动连接（simctl launch --args -txHost … -txAutoCommand …）。
    func autoConnectIfConfigured() {
        let d = UserDefaults.standard
        guard let host = d.string(forKey: "txHost"), !host.isEmpty,
              let user = d.string(forKey: "txUser") else { return }
        let port = d.integer(forKey: "txPort")
        autoCommand = d.string(forKey: "txAutoCommand")
        if let key = d.string(forKey: "txTsnetKey"), !key.isEmpty { tsnetAuthKey = key }
        connect(host: host, port: port == 0 ? 22 : port,
                username: user, password: d.string(forKey: "txPass") ?? "")
    }

    // MARK: - 状态机副作用执行

    private func run(_ effects: [SessionMachine.Effect]) {
        for effect in effects {
            switch effect {
            case .startConnect: startSession()
            case .scheduleReconnect(_, let delayMS): scheduleReconnect(delayMS)
            case .cancelReconnectTimer: reconnectTask?.cancel(); reconnectTask = nil
            case .teardownTransport: holder.transport?.stop()
            case .notify(let message): banner = message
            }
        }
        syncUI()
    }

    private func startSession() {
        guard let config else { return }
        if let key = tsnetAuthKey {
            // tsnet 模式：后台 up 节点 + dial fd，再用外部 fd 建 SSHSession。
            let mgr = tsnetMgr
            Task.detached {
                do {
                    try mgr.ensureUp(authKey: key, timeoutMs: 45000)
                    let fd = try mgr.dialFD(host: config.host, port: config.port, timeoutMs: 15000)
                    await MainActor.run { self.wireAndStart(SSHSession(config: config, preconnectedFD: fd)) }
                } catch {
                    await MainActor.run {
                        self.handleTransportState(.failed("tsnet: \(error.localizedDescription)"))
                    }
                }
            }
        } else {
            wireAndStart(SSHSession(config: config))
        }
    }

    private func wireAndStart(_ ssh: SSHSession) {
        exitTmux()   // 新会话回原始模式（tmux 会话在服务端，重连后需重新 -CC attach）
        let router = tmuxRouter
        ssh.onBytes = { data in router.feed(data) }   // 经路由器分流 raw / tmux 网关
        ssh.onState = { [weak self] newState in
            Task { @MainActor in self?.handleTransportState(newState) }
        }
        holder.transport = ssh
        ssh.start()
    }

    private lazy var tmuxRouter = TmuxRouter(
        rawGate: gate,
        enterGateway: { [weak self] after in
            Task { @MainActor in self?.enterTmux(initialBytes: after) }
        },
        gatewayBytes: { [weak self] bytes in
            Task { @MainActor in self?.tmuxController?.feed(Data(bytes)) }
        }
    )

    private func enterTmux(initialBytes: [UInt8]) {
        let holder = self.holder
        let controller = TmuxController(sendRaw: { data in holder.transport?.send(data) })
        controller.onExit = { [weak self] in Task { @MainActor in self?.exitTmux() } }
        tmuxController = controller
        if !initialBytes.isEmpty { controller.feed(Data(initialBytes)) }
    }

    private func exitTmux() {
        if tmuxController != nil { tmuxController = nil }
        tmuxRouter.reset()
    }

    private func handleTransportState(_ st: TransportState) {
        switch st {
        case .authenticating: run(machine.reduce(.authenticating))
        case .connected: run(machine.reduce(.established))
        case .disconnected(let reason): run(machine.reduce(.transportClosed(reason: reason)))
        case .failed(let message): run(machine.reduce(.authFailed(reason: message)))
        case .idle, .connecting: break
        }
    }

    private func scheduleReconnect(_ delayMS: Int) {
        reconnectTask?.cancel()
        reconnectTask = Task { [weak self] in
            try? await Task.sleep(nanoseconds: UInt64(delayMS) * 1_000_000)
            guard !Task.isCancelled else { return }
            await MainActor.run {
                guard let self else { return }
                self.run(self.machine.reduce(.reconnectTimerFired))
            }
        }
    }

    private func syncUI() {
        switch machine.phase {
        case .connected, .reconnecting, .waitingToReconnect, .backgroundParked:
            showsTerminal = true
        case .idle, .connecting, .authenticating, .closed, .failed:
            showsTerminal = false
        }
        phaseText = Self.describe(machine.phase)
    }

    private static func describe(_ phase: SessionMachine.Phase) -> String {
        switch phase {
        case .idle: "空闲"
        case .connecting: "连接中…"
        case .authenticating: "认证中…"
        case .connected: "已连接"
        case .backgroundParked: "已挂起（后台）"
        case .waitingToReconnect(let n): "等待重连（第 \(n) 次）"
        case .reconnecting(let n): "重连中（第 \(n) 次）"
        case .failed(let r): "失败：\(r)"
        case .closed: "已关闭"
        }
    }
}