package socks5

import (
	"encoding/binary"
	"fmt"
	"io"
	"net"
	"time"

	"github.com/sirupsen/logrus"
)

// SOCKS5 协议常量
const (
	// SOCKS版本
	Version5 = 0x05

	// 认证方法
	AuthNone        = 0x00
	AuthPassword    = 0x02
	AuthNoSupported = 0xFF

	// 命令类型
	CmdConnect = 0x01
	CmdBind    = 0x02
	CmdUDP     = 0x03

	// 地址类型
	AddrIPv4   = 0x01
	AddrDomain = 0x03
	AddrIPv6   = 0x04

	// 响应状态
	StatusSuccess              = 0x00
	StatusServerFailure        = 0x01
	StatusConnectionNotAllowed = 0x02
	StatusNetworkUnreachable   = 0x03
	StatusHostUnreachable      = 0x04
	StatusConnectionRefused    = 0x05
	StatusTTLExpired           = 0x06
	StatusCommandNotSupported  = 0x07
	StatusAddressNotSupported  = 0x08
)

type Server struct {
	logger   *logrus.Logger
	auth     AuthHandler
	dialer   Dialer
	resolver Resolver
	rules    []Rule
}

type Config struct {
	Auth    AuthConfig
	Timeout time.Duration
	Rules   []RuleConfig
}

type AuthConfig struct {
	Methods  []string
	Username string
	Password string
}

type RuleConfig struct {
	Action string // allow, deny
	IPs    []string
	Ports  []int
}

type AuthHandler interface {
	Authenticate(username, password string) bool
	Methods() []byte
}

type Dialer interface {
	Dial(network, address string) (net.Conn, error)
}

type Resolver interface {
	Resolve(domain string) (net.IP, error)
}

type Rule interface {
	Allow(addr net.Addr) bool
}

// NewServer 创建新的SOCKS5服务器
func NewServer(config Config, logger *logrus.Logger) *Server {
	server := &Server{
		logger:   logger,
		dialer:   &DirectDialer{timeout: config.Timeout},
		resolver: &DirectResolver{},
	}

	// 设置认证处理器
	server.auth = NewAuthHandler(config.Auth)

	// 设置访问规则
	for _, ruleConfig := range config.Rules {
		rule := NewRule(ruleConfig)
		server.rules = append(server.rules, rule)
	}

	return server
}

// HandleConnection 处理SOCKS5连接
func (s *Server) HandleConnection(conn net.Conn) error {
	defer conn.Close()

	s.logger.WithField("remote_addr", conn.RemoteAddr()).Debug("New SOCKS5 connection")

	// 设置连接超时
	conn.SetDeadline(time.Now().Add(30 * time.Second))

	// 1. 协议版本协商
	if err := s.handleVersionNegotiation(conn); err != nil {
		s.logger.WithError(err).Error("Version negotiation failed")
		return err
	}

	// 2. 认证
	if err := s.handleAuthentication(conn); err != nil {
		s.logger.WithError(err).Error("Authentication failed")
		return err
	}

	// 3. 处理请求
	return s.handleRequest(conn)
}

// handleVersionNegotiation 处理版本协商
func (s *Server) handleVersionNegotiation(conn net.Conn) error {
	// 读取客户端版本协商请求
	buf := make([]byte, 2)
	if _, err := io.ReadFull(conn, buf); err != nil {
		return fmt.Errorf("failed to read version: %w", err)
	}

	version := buf[0]
	nmethods := buf[1]

	if version != Version5 {
		return fmt.Errorf("unsupported SOCKS version: %d", version)
	}

	// 读取支持的认证方法
	methods := make([]byte, nmethods)
	if _, err := io.ReadFull(conn, methods); err != nil {
		return fmt.Errorf("failed to read methods: %w", err)
	}

	// 选择认证方法
	authMethods := s.auth.Methods()
	selectedMethod := byte(AuthNoSupported)

	for _, method := range methods {
		for _, supported := range authMethods {
			if method == supported {
				selectedMethod = method
				break
			}
		}
		if selectedMethod != AuthNoSupported {
			break
		}
	}

	// 发送选择的认证方法
	response := []byte{Version5, selectedMethod}
	if _, err := conn.Write(response); err != nil {
		return fmt.Errorf("failed to write method selection: %w", err)
	}

	if selectedMethod == AuthNoSupported {
		return fmt.Errorf("no supported authentication method")
	}

	return nil
}

// handleAuthentication 处理认证
func (s *Server) handleAuthentication(conn net.Conn) error {
	// 读取认证请求
	buf := make([]byte, 2)
	if _, err := io.ReadFull(conn, buf); err != nil {
		return fmt.Errorf("failed to read auth version: %w", err)
	}

	version := buf[0]
	usernameLen := buf[1]

	if version != 0x01 {
		return fmt.Errorf("unsupported auth version: %d", version)
	}

	// 读取用户名
	username := make([]byte, usernameLen)
	if _, err := io.ReadFull(conn, username); err != nil {
		return fmt.Errorf("failed to read username: %w", err)
	}

	// 读取密码长度
	if _, err := io.ReadFull(conn, buf[:1]); err != nil {
		return fmt.Errorf("failed to read password length: %w", err)
	}
	passwordLen := buf[0]

	// 读取密码
	password := make([]byte, passwordLen)
	if _, err := io.ReadFull(conn, password); err != nil {
		return fmt.Errorf("failed to read password: %w", err)
	}

	// 验证认证
	success := s.auth.Authenticate(string(username), string(password))

	// 发送认证结果
	status := byte(0x01) // 失败
	if success {
		status = 0x00 // 成功
	}

	response := []byte{0x01, status}
	if _, err := conn.Write(response); err != nil {
		return fmt.Errorf("failed to write auth response: %w", err)
	}

	if !success {
		return fmt.Errorf("authentication failed")
	}

	return nil
}

// handleRequest 处理SOCKS5请求
func (s *Server) handleRequest(conn net.Conn) error {
	// 读取请求头
	buf := make([]byte, 4)
	if _, err := io.ReadFull(conn, buf); err != nil {
		return fmt.Errorf("failed to read request header: %w", err)
	}

	version := buf[0]
	cmd := buf[1]
	// rsv := buf[2] // 保留字段
	addrType := buf[3]

	if version != Version5 {
		return fmt.Errorf("invalid SOCKS version: %d", version)
	}

	// 读取目标地址
	addr, err := s.readAddress(conn, addrType)
	if err != nil {
		s.sendResponse(conn, StatusServerFailure, "0.0.0.0", 0)
		return fmt.Errorf("failed to read address: %w", err)
	}

	// 检查访问规则
	if !s.checkRules(addr) {
		s.sendResponse(conn, StatusConnectionNotAllowed, "0.0.0.0", 0)
		return fmt.Errorf("connection not allowed: %s", addr)
	}

	// 处理不同的命令
	switch cmd {
	case CmdConnect:
		return s.handleConnect(conn, addr)
	case CmdBind:
		return s.handleBind(conn, addr)
	case CmdUDP:
		return s.handleUDP(conn, addr)
	default:
		s.sendResponse(conn, StatusCommandNotSupported, "0.0.0.0", 0)
		return fmt.Errorf("unsupported command: %d", cmd)
	}
}

// readAddress 读取地址信息
func (s *Server) readAddress(conn net.Conn, addrType byte) (string, error) {
	switch addrType {
	case AddrIPv4:
		buf := make([]byte, 6) // 4字节IP + 2字节端口
		if _, err := io.ReadFull(conn, buf); err != nil {
			return "", err
		}
		ip := net.IP(buf[:4])
		port := binary.BigEndian.Uint16(buf[4:6])
		return fmt.Sprintf("%s:%d", ip.String(), port), nil

	case AddrDomain:
		buf := make([]byte, 1)
		if _, err := io.ReadFull(conn, buf); err != nil {
			return "", err
		}
		domainLen := buf[0]

		domain := make([]byte, domainLen+2) // 域名 + 2字节端口
		if _, err := io.ReadFull(conn, domain); err != nil {
			return "", err
		}
		port := binary.BigEndian.Uint16(domain[domainLen:])
		return fmt.Sprintf("%s:%d", string(domain[:domainLen]), port), nil

	case AddrIPv6:
		buf := make([]byte, 18) // 16字节IP + 2字节端口
		if _, err := io.ReadFull(conn, buf); err != nil {
			return "", err
		}
		ip := net.IP(buf[:16])
		port := binary.BigEndian.Uint16(buf[16:18])
		return fmt.Sprintf("[%s]:%d", ip.String(), port), nil

	default:
		return "", fmt.Errorf("unsupported address type: %d", addrType)
	}
}

// handleConnect 处理CONNECT命令
func (s *Server) handleConnect(conn net.Conn, addr string) error {
	s.logger.WithField("target", addr).Debug("Handling CONNECT request")

	// 连接到目标服务器
	target, err := s.dialer.Dial("tcp", addr)
	if err != nil {
		s.logger.WithError(err).WithField("target", addr).Error("Failed to connect to target")
		s.sendResponse(conn, StatusConnectionRefused, "0.0.0.0", 0)
		return err
	}
	defer target.Close()

	// 发送成功响应
	localAddr := target.LocalAddr().(*net.TCPAddr)
	s.sendResponse(conn, StatusSuccess, localAddr.IP.String(), uint16(localAddr.Port))

	// 开始数据转发
	s.logger.WithField("target", addr).Info("Starting data relay")
	return s.relay(conn, target)
}

// handleBind 处理BIND命令
func (s *Server) handleBind(conn net.Conn, addr string) error {
	// BIND命令实现（简化版本）
	s.sendResponse(conn, StatusCommandNotSupported, "0.0.0.0", 0)
	return fmt.Errorf("BIND command not implemented")
}

// handleUDP 处理UDP命令
func (s *Server) handleUDP(conn net.Conn, addr string) error {
	// UDP关联实现（简化版本）
	s.sendResponse(conn, StatusCommandNotSupported, "0.0.0.0", 0)
	return fmt.Errorf("UDP command not implemented")
}

// sendResponse 发送SOCKS5响应
func (s *Server) sendResponse(conn net.Conn, status byte, ip string, port uint16) error {
	response := []byte{
		Version5,
		status,
		0x00, // 保留字段
		AddrIPv4,
	}

	// 添加IP地址
	ipAddr := net.ParseIP(ip)
	if ipAddr == nil {
		ipAddr = net.ParseIP("0.0.0.0")
	}
	if ipv4 := ipAddr.To4(); ipv4 != nil {
		response = append(response, ipv4...)
	} else {
		response[3] = AddrIPv6
		response = append(response, ipAddr.To16()...)
	}

	// 添加端口
	portBytes := make([]byte, 2)
	binary.BigEndian.PutUint16(portBytes, port)
	response = append(response, portBytes...)

	_, err := conn.Write(response)
	return err
}

// checkRules 检查访问规则
func (s *Server) checkRules(addr string) bool {
	if len(s.rules) == 0 {
		return true // 没有规则时允许所有连接
	}

	host, _, err := net.SplitHostPort(addr)
	if err != nil {
		return false
	}

	targetAddr, err := net.ResolveIPAddr("ip", host)
	if err != nil {
		return false
	}

	for _, rule := range s.rules {
		if rule.Allow(targetAddr) {
			return true
		}
	}

	return false
}

// relay 数据转发
func (s *Server) relay(client, target net.Conn) error {
	// 创建双向数据转发
	errChan := make(chan error, 2)

	// 客户端到目标服务器
	go func() {
		_, err := io.Copy(target, client)
		errChan <- err
	}()

	// 目标服务器到客户端
	go func() {
		_, err := io.Copy(client, target)
		errChan <- err
	}()

	// 等待任一方向的连接关闭
	err := <-errChan
	return err
}