//
//  SDLContextBootstrap.swift
//  Tun
//
//  Created by Codex on 2026/5/28.
//

import Foundation

final class SDLContextBootstrap: @unchecked Sendable {
    private typealias StartCompletion = (Error?) -> Void
    private typealias StopCompletion = () -> Void
    private typealias WakeCompletion = (Error?) -> Void

    private enum BootstrapCommand {
        case start(config: SDLConfiguration, rsaCipher: CCRSACipher, completion: StartCompletion)
        case stop(clearRuntimeConfiguration: Bool, completion: StopCompletion)
        case recoverAfterWake(completion: WakeCompletion)
    }

    private enum RuntimeState {
        case idle
        case starting
        case running
        case stopping
    }

    private weak var provider: PacketTunnelProvider?
    private let runtimeLock = NSLock()
    private var runtimeState: RuntimeState = .idle
    private var config: SDLConfiguration?
    private var rsaCipher: CCRSACipher?
    private var contextActor: SDLContextActor?
    private var startCompletionHandler: ((Error?) -> Void)?
    private let commandContinuation: AsyncStream<BootstrapCommand>.Continuation
    private var commandWorker: Task<Void, Never>?

    init(provider: PacketTunnelProvider) {
        let commandPair = AsyncStream.makeStream(of: BootstrapCommand.self, bufferingPolicy: .unbounded)

        self.provider = provider
        self.commandContinuation = commandPair.continuation
        let stream = commandPair.stream
        
        self.commandWorker = Task { [weak self] in
            await self?.runCommandLoop(stream)
        }
    }

    deinit {
        self.commandContinuation.finish()
        self.commandWorker?.cancel()
    }

    func startCached(completionHandler: @escaping (Error?) -> Void) {
        self.runtimeLock.lock()
        let config = self.config
        let rsaCipher = self.rsaCipher
        self.runtimeLock.unlock()

        guard let config, let rsaCipher else {
            SDLLogger.fatal("[SDLContextBootstrap] startCached failed: missing cached runtime configuration", category: .app)
            completionHandler(TunnelError.invalidConfiguration)
            return
        }

        self.start(config: config, rsaCipher: rsaCipher, completionHandler: completionHandler)
    }

    func start(config: SDLConfiguration, rsaCipher: CCRSACipher, completionHandler: @escaping (Error?) -> Void) {
        self.submit(.start(config: config, rsaCipher: rsaCipher, completion: completionHandler))
    }

    func stop(clearRuntimeConfiguration: Bool, completionHandler: @escaping () -> Void) {
        self.submit(.stop(clearRuntimeConfiguration: clearRuntimeConfiguration, completion: completionHandler))
    }

    func recoverAfterWake(completionHandler: @escaping (Error?) -> Void) {
        self.submit(.recoverAfterWake(completion: completionHandler))
    }

    func currentContextActor() -> SDLContextActor? {
        self.runtimeLock.lock()
        let contextActor = self.contextActor
        self.runtimeLock.unlock()
        return contextActor
    }

    private func submit(_ command: BootstrapCommand) {
        self.commandContinuation.yield(command)
    }

    private func runCommandLoop(_ stream: AsyncStream<BootstrapCommand>) async {
        for await command in stream {
            self.handle(command)
        }
    }

    private func handle(_ command: BootstrapCommand) {
        switch command {
        case .start(let config, let rsaCipher, let completion):
            self.handleStart(config: config, rsaCipher: rsaCipher, completionHandler: completion)
        case .stop(let clearRuntimeConfiguration, let completion):
            self.handleStop(clearRuntimeConfiguration: clearRuntimeConfiguration, completionHandler: completion)
        case .recoverAfterWake(let completion):
            self.handleRecoverAfterWake(completionHandler: completion)
        }
    }

    private func handleStart(config: SDLConfiguration, rsaCipher: CCRSACipher, completionHandler: @escaping (Error?) -> Void) {
        guard let provider = self.provider else {
            SDLLogger.fatal("[SDLContextBootstrap] start rejected: provider released", category: .app)
            completionHandler(TunnelError.invalidContext)
            return
        }

        self.runtimeLock.lock()
        switch self.runtimeState {
        case .idle:
            SDLTunnelAppNotifier.shared.clear()

            let contextActor = SDLContextActor(
                provider: provider,
                config: config,
                rsaCipher: rsaCipher
            )

            self.config = config
            self.rsaCipher = rsaCipher
            self.contextActor = contextActor
            self.startCompletionHandler = completionHandler
            self.runtimeState = .starting
            self.runtimeLock.unlock()

            Task {
                do {
                    try await contextActor.start()
                    self.finishContextStart(contextActor, error: nil)
                } catch {
                    SDLLogger.fatal("[SDLContextBootstrap] context start failed: \(error)", category: .app)
                    self.finishContextStart(contextActor, error: error)
                }
            }

        case .starting, .running, .stopping:
            SDLLogger.fatal("[SDLContextBootstrap] start rejected: invalid runtime state \(self.runtimeState)", category: .app)
            self.runtimeLock.unlock()
            completionHandler(TunnelError.invalidContext)
        }
    }

    private func handleStop(clearRuntimeConfiguration: Bool, completionHandler: @escaping () -> Void) {
        self.runtimeLock.lock()
        let contextActor = self.contextActor
        let startCompletionHandler = self.startCompletionHandler

        guard let contextActor else {
            SDLLogger.fatal("[SDLContextBootstrap] stop requested while context is nil, clearRuntimeConfiguration: \(clearRuntimeConfiguration)", category: .app)
            self.runtimeState = .idle
            self.startCompletionHandler = nil
            if clearRuntimeConfiguration {
                self.config = nil
                self.rsaCipher = nil
            }
            self.runtimeLock.unlock()
            startCompletionHandler?(TunnelError.invalidContext)
            completionHandler()
            return
        }

        self.contextActor = nil
        self.startCompletionHandler = nil
        self.runtimeState = .stopping
        if clearRuntimeConfiguration {
            self.config = nil
            self.rsaCipher = nil
        }
        self.runtimeLock.unlock()

        SDLLogger.fatal("[SDLContextBootstrap] stop will stop current context, clearRuntimeConfiguration: \(clearRuntimeConfiguration)", category: .app)
        startCompletionHandler?(TunnelError.invalidContext)

        Task {
            await contextActor.stop()
            self.markContextStopped()
            completionHandler()
        }
    }

    private func handleRecoverAfterWake(completionHandler: @escaping (Error?) -> Void) {
        self.runtimeLock.lock()
        let runtimeState = self.runtimeState
        let contextActor = self.contextActor
        let config = self.config
        let rsaCipher = self.rsaCipher
        self.runtimeLock.unlock()

        switch runtimeState {
        case .running:
            guard let contextActor else {
                SDLLogger.fatal("[SDLContextBootstrap] recoverAfterWake failed: missing running context", category: .app)
                completionHandler(TunnelError.invalidContext)
                return
            }

            Task {
                do {
                    try await contextActor.recoverAfterWake()
                    completionHandler(nil)
                } catch {
                    SDLLogger.fatal("[SDLContextBootstrap] recoverAfterWake failed: \(error)", category: .app)
                    completionHandler(error)
                }
            }

        case .idle:
            guard let config, let rsaCipher else {
                SDLLogger.fatal("[SDLContextBootstrap] recoverAfterWake failed: missing cached runtime configuration", category: .app)
                completionHandler(TunnelError.invalidConfiguration)
                return
            }

            SDLLogger.log("[SDLContextBootstrap] recoverAfterWake will start cached context", category: .app)
            self.handleStart(config: config, rsaCipher: rsaCipher, completionHandler: completionHandler)

        case .starting:
            SDLLogger.log("[SDLContextBootstrap] recoverAfterWake ignored while context is starting", category: .app)
            completionHandler(nil)

        case .stopping:
            SDLLogger.log("[SDLContextBootstrap] recoverAfterWake ignored while context is stopping", category: .app)
            completionHandler(nil)
        }
    }

    private func finishContextStart(_ contextActor: SDLContextActor, error: Error?) {
        self.runtimeLock.lock()
        guard self.contextActor === contextActor else {
            self.runtimeLock.unlock()
            return
        }

        let startCompletionHandler = self.startCompletionHandler
        self.startCompletionHandler = nil

        if let error {
            self.contextActor = nil
            self.runtimeState = .idle
        } else {
            self.runtimeState = .running
        }
        self.runtimeLock.unlock()

        startCompletionHandler?(error)
    }

    private func markContextStopped() {
        self.runtimeLock.lock()
        if self.contextActor == nil {
            self.runtimeState = .idle
        }
        self.runtimeLock.unlock()
    }
}