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

import Foundation
import NIOCore
import NIOPosix
import SwiftProtobuf

// 处理和sn-server服务器之间的通讯
final class SDLUDPHole: ChannelInboundHandler {
    typealias InboundIn = AddressedEnvelope<ByteBuffer>
    
    private enum State: Equatable {
        case idle
        case ready
        case stopping
        case stopped
    }
    
    private let group = MultiThreadedEventLoopGroup(numberOfThreads: 1)
    private var channel: Channel?
    private var closeFuture: EventLoopFuture<Void>?
    private var state: State = .idle
    private var didFinishMessageStream: Bool = false
    
    public let messageStream: AsyncStream<(SocketAddress, SDLHoleMessage)>
    private let messageContinuation: AsyncStream<(SocketAddress, SDLHoleMessage)>.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
    }
    
    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IPv6通配地址，依赖SwiftNIO创建dual-stack socket，同时接收IPv4/IPv6流量
        let channel = try bootstrap.bind(host: "::", port: 0).wait()
        self.channel = channel
        self.closeFuture = channel.closeFuture
        self.state = .ready
        precondition(channel.localAddress != nil, "UDP channel has no localAddress after bind")
        
        return channel.localAddress!
    }
    
    func waitClose() async throws {
        switch self.state {
        case .idle:
            SDLLogger.log("[SDLUDPHole] waitClose11", for: .debug)
            return
        case .ready, .stopping, .stopped:
            guard let closeFuture = self.closeFuture else {
                SDLLogger.log("[SDLUDPHole] waitClose22", for: .debug)
                return
            }
            try await closeFuture.get()
            SDLLogger.log("[SDLUDPHole] waitClose33", for: .debug)
        }
    }
    
    func stop() {
        switch self.state {
        case .stopping, .stopped:
            return
        case .idle:
            self.state = .stopped
            self.finishMessageStream()
            return
        case .ready:
            self.state = .stopping
        }
        
        self.finishMessageStream()
        self.channel?.close(promise: nil)
    }
    
    // --MARK: ChannelInboundHandler delegate

    func channelRead(context: ChannelHandlerContext, data: NIOAny) {
        guard case .ready = self.state else {
            return
        }
        
        let envelope = unwrapInboundIn(data)
        
        var buffer = envelope.data
        let remoteAddress = envelope.remoteAddress
        
        if let rawBytes = buffer.getBytes(at: buffer.readerIndex, length: buffer.readableBytes) {
            SDLLogger.log("[SDLUDPHole] get raw bytes: \(rawBytes.count), from: \(remoteAddress)", for: .debug)
        }
        
        do {
            if let message = try 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) {
        self.finishMessageStream()
        self.channel = nil
        self.state = .stopped
    }
    
    func errorCaught(context: ChannelHandlerContext, error: any Error) {
        SDLLogger.log("[SDLUDPHole] channel error: \(error)", for: .debug)
        self.finishMessageStream()
        if self.state != .stopped {
            self.state = .stopping
        }
        context.close(promise: nil)
    }
    
    // MARK: 处理写入逻辑
    func send(type: SDLPacketType, data: Data, remoteAddress: SocketAddress) {
        guard case .ready = self.state, 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)
        }
    }
    
    // --MARK: 编解码器
    private func decode(buffer: inout ByteBuffer) throws -> SDLHoleMessage? {
        guard let type = buffer.readInteger(as: UInt8.self),
              let packetType = SDLPacketType(rawValue: type) else {
            return nil
        }
        
        switch packetType {
        case .data:
            guard let bytes = buffer.readBytes(length: buffer.readableBytes),
                  let dataPacket = try? SDLData(serializedBytes: bytes) else {
                return nil
            }
            return .data(dataPacket)
        case .register:
            guard let bytes = buffer.readBytes(length: buffer.readableBytes),
               let registerPacket = try? SDLRegister(serializedBytes: bytes) else {
                return nil
            }
            return .register(registerPacket)
        case .registerAck:
            guard let bytes = buffer.readBytes(length: buffer.readableBytes),
               let registerAck = try? SDLRegisterAck(serializedBytes: bytes) else {
                return nil
            }
            return .registerAck(registerAck)
        case .stunProbeReply:
            guard let bytes = buffer.readBytes(length: buffer.readableBytes),
               let stunProbeReply = try? SDLStunProbeReply(serializedBytes: bytes) else {
                return nil
            }
            return .stunProbeReply(stunProbeReply)
        case .stunReply:
            guard let bytes = buffer.readBytes(length: buffer.readableBytes),
               let stunReply = try? SDLStunReply(serializedBytes: bytes) else {
                return nil
            }
            return .stunReply(stunReply)
        default:
            SDLLogger.log("SDLUDPHole decode miss type: \(type)", for: .debug)
            
            return nil
        }
    }
    
    private func finishMessageStream() {
        guard !self.didFinishMessageStream else {
            return
        }
        
        self.didFinishMessageStream = true
        self.messageContinuation.finish()
    }
    
    deinit {
        self.stop()
        try? self.group.syncShutdownGracefully()
    }
    
}