//
//  SDLanServer.swift
//  Tun
//
//  Created by 安礼成 on 2024/1/31.
//
import Foundation
import NIOCore
import NIOPosix
import SwiftProtobuf

enum SDLUDPHoleError: Error {
    case invalidLocalAddress
}

// 处理和sn-server服务器之间的通讯
final class SDLUDPHole: ChannelInboundHandler {
    typealias InboundIn = AddressedEnvelope<ByteBuffer>
    
    // 事件
    enum HoleEvent {
        case ready
        case closed
        case errorCaught
    }
    
    private var isStopped: Bool = false
    
    private let group = MultiThreadedEventLoopGroup(numberOfThreads: 1)
    private var channel: Channel?
    
    public let messageStream: AsyncStream<(SocketAddress, SDLHoleMessage)>
    private let messageContinuation: AsyncStream<(SocketAddress, SDLHoleMessage)>.Continuation
    
    // 事件相关逻辑
    public let eventStream: AsyncStream<HoleEvent>
    private let eventContinuation: AsyncStream<HoleEvent>.Continuation

    // 启动函数
    init() throws {
        let (stream, continuation) = AsyncStream.makeStream(of: (SocketAddress, SDLHoleMessage).self, bufferingPolicy: .bufferingNewest(2048))
        self.messageStream = stream
        self.messageContinuation = continuation
        
        let eventPair = AsyncStream.makeStream(of: HoleEvent.self)
        self.eventStream = eventPair.stream
        self.eventContinuation = eventPair.continuation
    }
    
    func start() throws -> SocketAddress {
        let bootstrap = DatagramBootstrap(group: group)
            .channelOption(ChannelOptions.socketOption(.so_reuseaddr), value: 1)
            .channelInitializer { channel in
                channel.pipeline.addHandler(self)
            }
        
        // 绑定到IPv4通配地址，只处理IPv4流量
        let channel = try bootstrap.bind(host: "0.0.0.0", port: 0).wait()
        guard let localAddress = channel.localAddress else {
            throw SDLUDPHoleError.invalidLocalAddress
        }
        
        self.channel = channel
        eventContinuation.yield(.ready)
        
        return localAddress
    }
    
    // --MARK: ChannelInboundHandler delegate
    
    func channelRead(context: ChannelHandlerContext, data: NIOAny) {
        let envelope = unwrapInboundIn(data)
        var buffer = envelope.data
        let remoteAddress = envelope.remoteAddress
        
        let byteCount = buffer.readableBytes - buffer.readerIndex
        SDLLogger.log("[SDLUDPHole] get raw bytes: \(byteCount), from: \(remoteAddress)", for: .debug)
        
        do {
            if let message = try SDLHoleMessage.decode(buffer: &buffer) {
                self.messageContinuation.yield((remoteAddress, message))
            } else {
                SDLLogger.log("[SDLUDPHole] decode message, get null", for: .debug)
            }
        } catch let err {
            SDLLogger.log("[SDLUDPHole] decode message, get error: \(err)", for: .debug)
        }
    }
    
    func channelInactive(context: ChannelHandlerContext) {
        SDLLogger.log("[SDLUDPHole] channelInactive", for: .debug)
        self.eventContinuation.yield(.closed)
    }
    
    func errorCaught(context: ChannelHandlerContext, error: any Error) {
        SDLLogger.log("[SDLUDPHole] channel error: \(error)", for: .debug)
        context.close(promise: nil)
        self.eventContinuation.yield(.errorCaught)
    }
    
    // MARK: 处理写入逻辑
    func send(type: SDLPacketType, data: Data, remoteAddress: SocketAddress) {
        guard let channel = self.channel else {
            return
        }
        
        var buffer = channel.allocator.buffer(capacity: data.count + 1)
        buffer.writeBytes([type.rawValue])
        buffer.writeBytes(data)
        
        let envelope = AddressedEnvelope<ByteBuffer>(remoteAddress: remoteAddress, data: buffer)
        _ = channel.eventLoop.submit {
            channel.writeAndFlush(envelope, promise: nil)
        }
    }
        
    func stop() {
        guard !self.isStopped else {
            return
        }
        
        self.isStopped = true
        
        SDLLogger.log("[SDLUDPHole] stop", for: .debug)
        self.messageContinuation.finish()
        self.eventContinuation.finish()
        self.channel = nil
        
        try? self.group.syncShutdownGracefully()
    }
    
}