//
//  PacketTunnelProvider.swift
//  punchnet
//
//  Created by 安礼成 on 2025/8/3.
//

import Foundation
import NetworkExtension

enum TunnelError: Error {
    case invalidConfiguration
    case invalidContext
}

class PacketTunnelProvider: NEPacketTunnelProvider {
    private var runtimeEnv: SDLRuntimeEnvironment?
    
    override func startTunnel(options: [String: NSObject]?, completionHandler: @escaping (Error?) -> Void) {
        // 如果当前在运行状态，不允许重复请求
        guard self.runtimeEnv == nil else {
            completionHandler(TunnelError.invalidContext)
            return
        }
        
        guard let options, let config = SDLConfiguration.parse(options: options) else {
            completionHandler(TunnelError.invalidConfiguration)
            return
        }
        
        let rsaCipher = try! CCRSACipher(keySize: 1024)
        self.runtimeEnv = SDLRuntimeEnvironment(config: config, rsaCipher: rsaCipher)
        Task {
            do {
                try await self.runtimeEnv?.start(provider: self)
                completionHandler(nil)
            } catch let err {
                completionHandler(err)
            }
        }
        
    }

    override func stopTunnel(with reason: NEProviderStopReason, completionHandler: @escaping () -> Void) {
        // Add code here to start the process of stopping the tunnel.
        Task {
            await self.runtimeEnv?.stop()
            completionHandler()
        }
    }

    override func handleAppMessage(_ messageData: Data, completionHandler: ((Data?) -> Void)?) {
        // Add code here to handle the message.
        Task {
            do {
                let message = try AppRequest(serializedBytes: messageData)
                let replyData = try await self.handleAppRequest(message: message)
                completionHandler?(replyData)
            } catch let err {
                var reply = TunnelResponse()
                reply.code = 1
                reply.message = err.localizedDescription

                let errorReplyData = try? reply.serializedData()
                completionHandler?(errorReplyData)
            }
        }
    }

    override func sleep(completionHandler: @escaping () -> Void) {
        // Add code here to get ready to sleep.
        Task {
            await self.runtimeEnv?.stop()
            completionHandler()
        }
    }

    override func wake() {
        SDLLogger.log("[PacketTunnelProvider] wake up!!!!!!!")
        // 启动monitor
        let monitor = SDLPathMonitor()
        // 启动监视器，允许重入
        monitor.start()
        SDLLogger.log("[PacketTunnelProvider] monitor started")
        
        // Add code here to wake up.
        Task {
            
            defer {
                monitor.stop()
            }
            
            // 等待网络可达
            _ = await monitor.statusStream().first {$0 == .satisfied}
            SDLLogger.log("[PacketTunnelProvider] network is satisfied")
            // 重新启动
            try await self.runtimeEnv?.start(provider: self)
        }
        
    }

    private func handleAppRequest(message: AppRequest) async throws -> Data? {
        guard let contextActor = self.runtimeEnv?.getContextActor() else {
            throw TunnelError.invalidContext
        }
        
        switch message.command {
        case .changeExitNode(let changeExitNode):
            let exitNodeIp = changeExitNode.ip
            do {
                try await contextActor.updateExitNode(exitNodeIp: exitNodeIp)
                var reply = TunnelResponse()
                reply.code = 0
                reply.message = "操作成功"
                return try reply.serializedData()
                
            } catch let err {
                var reply = TunnelResponse()
                reply.code = 1
                reply.message = err.localizedDescription
                
                return try reply.serializedData()
            }
        case .none:
            var reply = TunnelResponse()
            reply.code = 1
            reply.message = "无效请求"
            return try reply.serializedData()
        }
    }

}

private class SDLRuntimeEnvironment {
    private enum State {
        case idle
        case starting
        case running
        case stopping
    }

    private let stateLock = NSLock()
    private var state: State = .idle
    private var pendingStop = false
    private weak var pendingStartProvider: PacketTunnelProvider?
    private var contextActor: SDLContextActor?
    private var config: SDLConfiguration
    private let rsaCipher: CCRSACipher
     
    init(config: SDLConfiguration, rsaCipher: CCRSACipher) {
        self.config = config
        self.rsaCipher = rsaCipher
    }
    
    func start(provider: PacketTunnelProvider) async throws {
        guard self.markStarting(provider: provider) else {
            return
        }
        
        // 重置通知中心
        SDLTunnelAppNotifier.shared.clear()
        
        let contextActor = SDLContextActor(provider: provider, config: config, rsaCipher: self.rsaCipher)
        await contextActor.start()
        
        let shouldStop = self.markStarted(contextActor: contextActor)
        if shouldStop {
            await self.stop()
        }
    }
    
    func getContextActor() -> SDLContextActor? {
        return self.withStateLock {
            self.contextActor
        }
    }
    
    func stop() async {
        guard let contextActor = self.markStopping() else {
            return
        }

        await contextActor.stop()

        if let provider = self.markStopped() {
            try? await self.start(provider: provider)
        }
    }

    private func markStarting(provider: PacketTunnelProvider) -> Bool {
        return self.withStateLock {
            switch self.state {
            case .idle:
                self.pendingStop = false
                self.pendingStartProvider = nil
                self.state = .starting
                return true

            case .starting, .running:
                SDLLogger.log("[SDLRuntimeEnvironment] skip duplicated start: \(self.state)", for: .debug)
                return false

            case .stopping:
                self.pendingStartProvider = provider
                SDLLogger.log("[SDLRuntimeEnvironment] delay start until stop finishes", for: .debug)
                return false
            }
        }
    }

    private func markStarted(contextActor: SDLContextActor) -> Bool {
        return self.withStateLock {
            self.contextActor = contextActor
            self.state = .running

            let shouldStop = self.pendingStop
            self.pendingStop = false
            return shouldStop
        }
    }

    private func markStartFailed() {
        self.withStateLock {
            self.contextActor = nil
            self.pendingStop = false
            self.pendingStartProvider = nil
            self.state = .idle
        }
    }

    private func markStopping() -> SDLContextActor? {
        return self.withStateLock {
            switch self.state {
            case .idle:
                self.contextActor = nil
                self.pendingStop = false
                return nil

            case .starting:
                self.pendingStop = true
                SDLLogger.log("[SDLRuntimeEnvironment] delay stop until start finishes", for: .debug)
                return nil

            case .stopping:
                SDLLogger.log("[SDLRuntimeEnvironment] skip duplicated stop", for: .debug)
                return nil

            case .running:
                self.state = .stopping
                let contextActor = self.contextActor
                self.contextActor = nil
                self.pendingStop = false
                return contextActor
            }
        }
    }

    private func markStopped() -> PacketTunnelProvider? {
        return self.withStateLock {
            self.state = .idle
            let provider = self.pendingStartProvider
            self.pendingStartProvider = nil
            return provider
        }
    }

    private func withStateLock<T>(_ body: () -> T) -> T {
        self.stateLock.lock()
        defer {
            self.stateLock.unlock()
        }
        return body()
    }
    
}