package fwd

import (
	"bufio"
	"context"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net"
	"proxy-server/gateway/app"
	"proxy-server/gateway/env"
	"proxy-server/utils"
	"strconv"
	"time"
)

type CtrlCmdType int

const (
	CtrlCmdPong CtrlCmdType = iota + 1
	CtrlCmdPing
	CtrlCmdOpen
	CtrlCmdClose
	CtrlCmdProxy
)

func ListenCtrl(ctx context.Context) error {
	ctrlPort := env.AppCtrlPort

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

	// 异步等待处理连接
	var connCh = make(chan net.Conn)
	go func() {
		for {
			conn, err := ls.Accept()
			if errors.Is(err, net.ErrClosed) {
				slog.Debug("控制通道监听关闭")
				return
			}
			if err != nil {
				slog.Error("接受控制通道连接失败", "err", err)
				return
			}
			select {
			case connCh <- conn:
			case <-ctx.Done():
				utils.Close(conn)
				return
			}
		}
	}()

	err = nil
	for {
		select {
		case <-ctx.Done():
			return nil
		case conn := <-connCh:
			app.CtrlConnWg.Add(1)
			go func() {
				defer app.CtrlConnWg.Done()
				defer utils.Close(conn)
				err := processCtrlConn(ctx, conn)
				if err != nil {
					slog.Error("处理控制通道连接失败", "err", err)
				}
			}()
		}
	}
}

func processCtrlConn(_ctx context.Context, conn net.Conn) (err error) {
	reader := bufio.NewReader(conn)

	// 上下文与通道信息
	ctx, cancel := context.WithCancel(_ctx)
	defer cancel()

	// 结束时清理
	var edgeId int32
	defer func() {
		var edge, ok = app.Edges.Load(edgeId)
		if ok {
			*edge.Status = 0
		}
	}()

	// 处理连接命令
	var errCh = make(chan error)
	go func() {
		var err error
		for {
			// 读取命令
			var timeout = time.Duration(env.AppCtrlHBTimeout*2+env.AppCtrlRWTimeout) * time.Second
			err = conn.SetReadDeadline(time.Now().Add(timeout))
			if err != nil {
				errCh <- fmt.Errorf("设置读取超时失败: %w", err)
				return
			}

			cmd, err := reader.ReadByte()
			if ok, err := utils.WarpConnErr(err); !ok {
				errCh <- err
				return
			}

			// 处理节点命令
			err = conn.SetReadDeadline(time.Now().Add(time.Duration(env.AppCtrlRWTimeout) * time.Second))
			if err != nil {
				errCh <- fmt.Errorf("设置读取超时失败: %w", err)
				return
			}
			switch CtrlCmdType(cmd) {

			// 连接建立命令
			case CtrlCmdOpen:
				var recv = make([]byte, 4)
				_, err = io.ReadFull(reader, recv)
				if err != nil {
					errCh <- fmt.Errorf("读取节点 ID 失败: %w", err)
					return
				}
				edgeId = int32(binary.BigEndian.Uint32(recv))
				err = onOpen(ctx, conn, edgeId, conn.RemoteAddr())
				if err != nil {
					errCh <- fmt.Errorf("处理连接建立命令失败: %w", err)
					return
				}

			// 心跳命令
			case CtrlCmdPing:
				err = onPing(conn)
				if err != nil {
					errCh <- fmt.Errorf("处理心跳命令失败: %w", err)
					return
				}

			// 连接关闭命令
			case CtrlCmdClose:
				err = onClose(conn)
				if err != nil {
					errCh <- fmt.Errorf("处理关闭命令失败: %w", err)
					return
				}

			// 忽略其他不应该由节点发起的命令
			default:
				errCh <- fmt.Errorf("无法处理控制命令: %d", cmd)
				return
			}
		}
	}()

	// 等待处理结束
	select {
	case <-ctx.Done():
	case err = <-errCh:
	}

	return
}

func onOpen(ctx context.Context, writer io.Writer, edgeId int32, addr net.Addr) (err error) {
	tcpAddr, ok := addr.(*net.TCPAddr)
	if !ok {
		return fmt.Errorf("无效的地址类型: %T", addr)
	}

	var port uint16
	edge, ok := app.Edges.Load(edgeId)
	if !ok || edge.Port == nil {
		// 分配端口
		app.LockPortAssign.Lock()

		var minim uint16 = 20000
		var maxim uint16 = 60000
		for i := minim; i < maxim; i++ {
			var _, ok = app.Assigns.Load(i)
			if !ok {
				port = i
				break
			}
		}
		if port == 0 {
			return errors.New("没有可用的端口")
		}

		err := app.NewEdge(edgeId, port, tcpAddr)
		if err != nil {
			return fmt.Errorf("新增边缘节点失败：%w", err)
		}

		app.LockPortAssign.Unlock()
	} else {
		// 更新边缘节点地址
		port = *edge.Port
		err := app.TryUpdateEdge(edgeId, tcpAddr)
		if err != nil {
			return fmt.Errorf("尝试更新边缘节点失败: %w", err)
		}
	}

	// 启动转发服务
	app.FwdLesWg.Add(1)
	go func() {
		defer app.FwdLesWg.Done()
		slog.Info("监听转发端口", "port", port, "edge", edgeId)
		err = ListenUser(ctx, port, writer)
		if err != nil {
			slog.Error("监听转发端口失败", "port", port, "edge", edgeId, "err", err)
		}
	}()

	// 响应节点
	if err = sendPong(writer); err != nil {
		return fmt.Errorf("响应节点失败: %w", err)
	}

	return nil
}

func onPing(writer io.Writer) (err error) {
	return sendPong(writer)
}

func onClose(writer io.Writer) (err error) {
	return sendPong(writer)
}

func sendPong(writer io.Writer) (err error) {
	_, err = writer.Write([]byte{byte(CtrlCmdPong)})
	if err != nil {
		return fmt.Errorf("响应节点失败: %w", err)
	}
	return nil
}

func sendProxy(writer io.Writer, tag [16]byte, addr string) (err error) {
	if len(addr) > 65535 {
		return fmt.Errorf("代理地址过长: %s", addr)
	}

	buf := make([]byte, 1+16+2+len(addr))
	buf[0] = byte(CtrlCmdProxy)
	copy(buf[1:], tag[:])
	binary.BigEndian.PutUint16(buf[17:], uint16(len(addr)))
	copy(buf[19:], addr)

	_, err = writer.Write(buf)
	if err != nil {
		return fmt.Errorf("发送代理命令失败: %w", err)
	}
	return nil
}