//
//  SDLanServer.swift
//  Tun
//
//  Created by 安礼成 on 2024/1/31.
//

import Foundation
import NIOCore
import NIOPosix

// 处理和sn-server服务器之间的通讯
actor SDLUDPHoleActor {
    private let group = MultiThreadedEventLoopGroup(numberOfThreads: 1)
    private let asyncChannel: NIOAsyncChannel<AddressedEnvelope<ByteBuffer>, AddressedEnvelope<ByteBuffer>>
    private let (writeStream, writeContinuation) = AsyncStream.makeStream(of: UDPMessage.self, bufferingPolicy: .unbounded)
    
    private var cookieGenerator = SDLIdGenerator(seed: 1)
    private var promises: [UInt32:EventLoopPromise<SDLStunProbeReply>] = [:]
    public var localAddress: SocketAddress?
    
    public let eventFlow: AsyncStream<UDPEvent>
    private let eventContinuation: AsyncStream<UDPEvent>.Continuation
    
    private let logger: SDLLogger
    
    // 依赖的外表能力
    struct Capabilities {
        let logger: @Sendable (String) async -> Void
        
    }
    
    struct UDPMessage {
        let remoteAddress: SocketAddress
        let type: SDLPacketType
        let data: Data
    }

    // 定义事件类型
    enum UDPEvent {
        case ready
        case message(SocketAddress, SDLHoleInboundMessage)
        case data(SDLData)
    }
    
    // 启动函数
    init(logger: SDLLogger) async throws {
        self.logger = logger
        
        (self.eventFlow, self.eventContinuation) = AsyncStream.makeStream(of: UDPEvent.self, bufferingPolicy: .unbounded)
        
        let bootstrap = DatagramBootstrap(group: group)
            .channelOption(ChannelOptions.socketOption(.so_reuseaddr), value: 1)
        
        self.asyncChannel = try await bootstrap.bind(host: "0.0.0.0", port: 0)
            .flatMapThrowing { channel in
                return try NIOAsyncChannel(wrappingChannelSynchronously: channel, configuration: .init(
                    inboundType: AddressedEnvelope<ByteBuffer>.self,
                    outboundType: AddressedEnvelope<ByteBuffer>.self
                ))
            }
            .get()
        
        self.localAddress = self.asyncChannel.channel.localAddress
        self.logger.log("[UDPHole] started and listening on: \(self.localAddress!)", level: .debug)
    }
    
    func start() async throws {
        try await withTaskCancellationHandler {
            try await self.asyncChannel.executeThenClose {inbound, outbound in
                self.eventContinuation.yield(.ready)
                try await withThrowingTaskGroup(of: Void.self) { group in
                    group.addTask {
                        defer {
                            self.logger.log("[SDLUDPHole] inbound closed", level: .warning)
                        }
                        
                        for try await envelope in inbound {
                            try Task.checkCancellation()
                            
                            var buffer = envelope.data
                            let remoteAddress = envelope.remoteAddress
                            do {
                                if let message = try Self.decode(buffer: &buffer) {
                                    switch message {
                                    case .data(let data):
                                        self.logger.log("[SDLUDPHole] read data: \(data.format()), from: \(remoteAddress)", level: .debug)
                                        self.eventContinuation.yield(.data(data))
                                    case .stunProbeReply(let probeReply):
                                        // 执行并移除回调
                                        await self.trigger(probeReply: probeReply)
                                    default:
                                        self.eventContinuation.yield(.message(remoteAddress, message))
                                    }
                                } else {
                                    self.logger.log("[SDLUDPHole] decode message, get null", level: .warning)
                                }
                            } catch let err {
                                self.logger.log("[SDLUDPHole] decode message, get error: \(err)", level: .warning)
                                throw err
                            }
                        }
                    }
                    
                    group.addTask {
                        defer {
                            self.logger.log("[SDLUDPHole] outbound closed", level: .warning)
                        }
                        
                        for await message in self.writeStream {
                            try Task.checkCancellation()
                            
                            var buffer = self.asyncChannel.channel.allocator.buffer(capacity: message.data.count + 1)
                            buffer.writeBytes([message.type.rawValue])
                            buffer.writeBytes(message.data)
                            
                            let envelope = AddressedEnvelope<ByteBuffer>(remoteAddress: message.remoteAddress, data: buffer)
                            try await outbound.write(envelope)
                        }
                    }
                    
                    if let _ = try await group.next() {
                        group.cancelAll()
                    }
                }
            }
        } onCancel: {
            self.writeContinuation.finish()
            self.eventContinuation.finish()
            self.logger.log("[SDLUDPHole] withTaskCancellationHandler cancel")
        }
    }
    
    func getCookieId() -> UInt32 {
        return self.cookieGenerator.nextId()
    }
    
    // 探测tun信息
    func stunProbe(remoteAddress: SocketAddress, attr: SDLProbeAttr = .none, timeout: Int = 5) async throws -> SDLStunProbeReply {
        return try await self._stunProbe(remoteAddress: remoteAddress, attr: attr, timeout: timeout).get()
    }
    
    private func _stunProbe(remoteAddress: SocketAddress, attr: SDLProbeAttr = .none, timeout: Int) -> EventLoopFuture<SDLStunProbeReply> {
        let cookie = self.cookieGenerator.nextId()
        var stunProbe = SDLStunProbe()
        stunProbe.cookie = cookie
        stunProbe.attr = UInt32(attr.rawValue)
        self.send( type: .stunProbe, data: try! stunProbe.serializedData(), remoteAddress: remoteAddress)
        self.logger.log("[SDLUDPHole] stunProbe: \(remoteAddress)", level: .debug)
        
        let promise = self.asyncChannel.channel.eventLoop.makePromise(of: SDLStunProbeReply.self)
        self.promises[cookie] = promise
        
        return promise.futureResult
    }
    
    private func trigger(probeReply: SDLStunProbeReply) {
        let id = probeReply.cookie
        // 执行并移除回调
        if let promise = self.promises[id] {
            self.asyncChannel.channel.eventLoop.execute {
                promise.succeed(probeReply)
            }
            self.promises.removeValue(forKey: id)
        }
    }
    
    // MARK: client-client apis
    // 处理写入逻辑
    func send(type: SDLPacketType, data: Data, remoteAddress: SocketAddress) {
        let message = UDPMessage(remoteAddress: remoteAddress, type: type, data: data)
        self.writeContinuation.yield(message)
    }
    
    //--MARK: 编解码器
    private static func decode(buffer: inout ByteBuffer) throws -> SDLHoleInboundMessage? {
        guard let type = buffer.readInteger(as: UInt8.self),
              let packetType = SDLPacketType(rawValue: type),
              let bytes = buffer.readBytes(length: buffer.readableBytes) else {
            return nil
        }
        
        switch packetType {
        case .data:
            let dataPacket = try SDLData(serializedBytes: bytes)
            return .data(dataPacket)
        case .register:
            let registerPacket = try SDLRegister(serializedBytes: bytes)
            return .register(registerPacket)
        case .registerAck:
            let registerAck = try SDLRegisterAck(serializedBytes: bytes)
            return .registerAck(registerAck)
        case .stunReply:
            let stunReply = try SDLStunReply(serializedBytes: bytes)
            return .stunReply(stunReply)
        case .stunProbeReply:
            let stunProbeReply = try SDLStunProbeReply(serializedBytes: bytes)
            return .stunProbeReply(stunProbeReply)
        default:
            return nil
        }
    }
    
    deinit {
        try? self.group.syncShutdownGracefully()
        self.writeContinuation.finish()
        self.eventContinuation.finish()
    }
    
}