package fwd

import (
	"bufio"
	"context"
	"log/slog"
	"net"
	"proxy-server/pkg/utils"
	"proxy-server/server/fwd/core"
	"proxy-server/server/fwd/dispatcher"
	"proxy-server/server/fwd/metrics"
	"proxy-server/server/fwd/repo"
	"proxy-server/server/pkg/env"
	"proxy-server/server/pkg/orm"
	"strconv"
	"strings"
	"time"

	"github.com/pkg/errors"
)

type CtrlCmd struct {
	conn net.Conn
	buf  []byte
}

var ctrlCmdChan = make(chan CtrlCmd, 1024)

func (s *Service) startCtrlTun() error {
	ctrlPort := env.AppCtrlPort
	slog.Debug("监听控制通道", slog.Uint64("port", uint64(ctrlPort)))

	// 监听端口
	ls, err := net.Listen("tcp", ":"+strconv.Itoa(int(ctrlPort)))
	if err != nil {
		return errors.Wrap(err, "监听控制通道失败")
	}
	defer utils.Close(ls)

	// 处理连接
	connCh := utils.ChanConnAccept(s.ctx, ls)
	err = nil
	for loop := true; loop; {
		select {
		case <-s.ctx.Done():
			loop = false
		case conn, ok := <-connCh:
			if !ok {
				err = errors.New("获取连接失败")
				loop = false
			}
			s.ctrlConnWg.Add(1)
			go func() {
				defer s.ctrlConnWg.Done()
				defer utils.Close(conn)
				err := s.processCtrlConn(conn)
				if err != nil {
					slog.Error("处理控制通道连接失败", "err", err)
				}
			}()
		}
	}

	return err
}

func (s *Service) processCtrlConn(conn net.Conn) error {
	reader := bufio.NewReader(conn)

	// version
	version, err := reader.ReadByte()
	if err != nil {
		_ = ctrlResp(conn, CtrlFail)
		return errors.Wrap(err, "获取版本号失败")
	}

	// name
	nameLen, err := reader.ReadByte()
	if err != nil {
		_ = ctrlResp(conn, CtrlFail)
		return errors.Wrap(err, "获取 name 失败")
	}
	nameBuf, err := utils.ReadBuffer(reader, int(nameLen))
	if err != nil {
		_ = ctrlResp(conn, CtrlFail)
		return errors.Wrap(err, "获取 name 失败")
	}
	name := string(nameBuf)

	if name == "" {
		_ = ctrlResp(conn, CtrlFail)
		return errors.New("客户端名称不能为空")
	}

	// 检查客户端
	var node repo.Node
	err = orm.DB.Take(&node, &repo.Node{
		Name: name,
	}).Error
	if err != nil {
		_ = ctrlResp(conn, CtrlFail)
		return errors.Wrap(err, "查询客户端失败")
	}

	if version != node.Version {
		_ = ctrlResp(conn, CtrlFail)
		return errors.New("客户端版本不匹配")
	}

	err = ctrlResp(conn, CtrlDone)
	if err != nil {
		return errors.Wrap(err, "向客户端发送响应失败")
	}

	port := node.FwdPort
	slog.Info("监听转发端口", "port", port, "client", name)

	// 启动转发服务
	proxy, err := dispatcher.New(port)
	if err != nil {
		return errors.Wrap(err, "创建 socks 转发服务失败")
	}
	defer proxy.Close()

	s.fwdLesWg.Add(1)
	go func() {
		defer s.fwdLesWg.Done()
		err := proxy.Run()
		if err != nil {
			slog.Error("代理服务运行失败", "err", err)
		}
	}()

	// 监听控制通道连接
	errCh := make(chan error, 1)
	go func() {
		defer close(errCh)
		_, err := reader.ReadByte()
		errCh <- err
	}()

	// 批量同步写入
	go func() {
		for {
			select {
			case <-s.ctx.Done():
				return
			case cmd := <-ctrlCmdChan:
				_, err := cmd.conn.Write(cmd.buf)
				if err != nil {
					slog.Error("批量写入失败", "err", err)
					utils.Close(cmd.conn)
				}
			}
		}
	}()

	// 处理连接
	for {
		select {
		case <-s.ctx.Done():
			return nil
		case err := <-errCh:
			switch {
			case strings.Contains(err.Error(), "An existing connection was forcibly closed by the remote host."):
				slog.Debug("客户端主动断开连接")
				return nil
			case err == nil:
				return errors.New("客户端握手失败")
			default:
				return errors.Wrap(err, "客户端意外断开连接")
			}
		case user := <-proxy.Conn:
			metrics.TimerAuth.Store(user.Conn, time.Now())
			s.userConnWg.Add(1)
			go func() {
				defer s.userConnWg.Done()
				err := s.processUserConn(user, conn)
				if err != nil {
					slog.Error("处理用户连接失败", "err", err)
					utils.Close(user)
				}
			}()
		}
	}
}

func (s *Service) processUserConn(user *core.Conn, ctrl net.Conn) error {

	// 组织写入信息
	dst := user.DestAddr().String()
	dstLen := len(dst)

	tag := user.Tag
	tagLen := len(tag)

	writeBuf := make([]byte, 2+dstLen+tagLen)
	writeBuf[0] = byte(dstLen)
	copy(writeBuf[1:], dst)
	writeBuf[1+dstLen] = byte(tagLen)
	copy(writeBuf[2+dstLen:], tag)

	// 异步写入命令
	ctrlCmdChan <- CtrlCmd{
		conn: ctrl,
		buf:  writeBuf,
	}

	// 记录用户连接
	s.userConnMap.Store(user.Tag, user)

	// 如果限定时间内没有建立数据通道，则关闭连接
	timeout, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	select {
	case <-s.ctx.Done():
		// 服务会在退出时统一关闭未消费的连接
	case <-timeout.Done():
		storedUser, ok := s.userConnMap.LoadAndDelete(user.Tag)
		if ok {
			slog.Debug("建立数据通道超时", "tag", user.Tag)
			utils.Close(storedUser)
		}
	}

	return nil
}

type CtrlResult byte

const (
	CtrlFail CtrlResult = iota
	CtrlDone
)

func ctrlResp(conn net.Conn, result CtrlResult) error {
	_, err := conn.Write([]byte{byte(result)})
	return err
}