package socks5

import (
	"context"
	"errors"
	"fmt"
	"io"
	"net"
	"time"
)

var (
	// ErrNetworkNotImplemented is the network not implemented error
	ErrNetworkNotImplemented = errors.New("network not implemented")
)

var (
	noDeadline      = time.Time{}
	expiredDeadline = time.Unix(1, 0)
)

// Dialer is the socks5 dialer
type Dialer struct {
	Server    string
	Username  string
	Password  string
	ProxyDial func(ctx context.Context, network string, addr string) (net.Conn, error)
}

func (s *Dialer) Dial(network string, address string) (net.Conn, error) {
	return s.DialContext(context.Background(), network, address)
}

func (s *Dialer) DialContext(ctx context.Context, network string, address string) (net.Conn, error) {
	proxy, err := AddrFromString(s.Server)
	if err != nil {
		return nil, &net.OpError{Op: "socks", Net: network, Source: proxy, Addr: AddrZero, Err: err}
	}

	addr, err := AddrFromString(address)
	if err != nil {
		return nil, &net.OpError{Op: "socks", Net: network, Source: proxy, Addr: AddrZero, Err: err}
	}

	switch network {
	case "tcp", "tcp4", "tcp6":
	case "udp", "udp4", "udp6":
	default:
		return nil, &net.OpError{Op: "socks", Net: network, Source: proxy, Addr: addr, Err: ErrNetworkNotImplemented}
	}

	var conn net.Conn
	if s.ProxyDial != nil {
		conn, err = s.ProxyDial(ctx, "tcp", s.Server)
	} else {
		var dd net.Dialer
		conn, err = dd.DialContext(ctx, "tcp", s.Server)
	}

	if err != nil {
		return nil, &net.OpError{Op: "socks", Net: "tcp", Source: proxy, Addr: addr, Err: err}
	}

	if deadline, ok := ctx.Deadline(); ok && !deadline.IsZero() {
		conn.SetDeadline(deadline)
		defer conn.SetDeadline(noDeadline)
	}

	var ctxErr error
	if ctx != context.Background() {
		errCh := make(chan error, 1)
		doneCh := make(chan struct{})

		defer func() {
			close(doneCh)
			if ctxErr == nil {
				ctxErr = <-errCh
			}
		}()

		go func() {
			select {
			case <-ctx.Done():
				conn.SetDeadline(expiredDeadline)
				errCh <- ctx.Err()
			case <-doneCh:
				errCh <- nil
			}
		}()
	}

	if err := s.negotiate(conn); err != nil {
		conn.Close()
		return nil, &net.OpError{Op: "socks", Net: "tcp", Source: proxy, Addr: addr, Err: err}
	}

	if network == "udp" || network == "udp4" || network == "udp6" {
		uc, err := s.handleUDP(conn, addr)
		if err != nil {
			conn.Close()
			return nil, &net.OpError{Op: "socks", Net: "udp", Source: proxy, Addr: addr, Err: err}
		}

		return uc, ctxErr
	}

	if err := s.handleTCP(conn, addr); err != nil {
		conn.Close()
		return nil, &net.OpError{Op: "socks", Net: "tcp", Source: proxy, Addr: addr, Err: err}
	}

	return conn, ctxErr
}

func (s *Dialer) DialUDP() (net.PacketConn, error) {
	conn, err := s.DialContext(context.Background(), "udp", "")
	return conn.(net.PacketConn), err
}

func (s *Dialer) handleTCP(conn net.Conn, addr *Addr) error {
	atyp, host, port := addr.Socks()

	req := NewRequest(CommandConnect, atyp, host, port)
	if _, err := req.WriteTo(conn); err != nil {
		return err
	}

	rep, err := NewReplyFrom(conn)
	if err != nil {
		return err
	}

	if rep.Status != ReplyStatusSuccess {
		return fmt.Errorf("bad reply status: %s", rep.Status)
	}

	return nil
}

func (s *Dialer) handleUDP(conn net.Conn, addr *Addr) (*UDPConn, error) {
	atyp, host, port := addr.Socks()

	req := NewRequest(CommandUDPAssociate, atyp, host, port)
	if _, err := req.WriteTo(conn); err != nil {
		return nil, err
	}

	rep, err := NewReplyFrom(conn)
	if err != nil {
		return nil, err
	}

	if rep.Status != ReplyStatusSuccess {
		return nil, fmt.Errorf("bad reply status: %s", rep.Status)
	}

	packetConn, err := net.ListenPacket("udp", "")
	if err != nil {
		return nil, err
	}

	go func() {
		io.Copy(io.Discard, conn)
		conn.Close()
		packetConn.Close()
	}()

	remoteAddr, err := AddrFromSocks(rep.ATYP, rep.BindAddr, rep.BindPort).UDP()
	if err != nil {
		return nil, err
	}

	if remoteAddr.IP.IsUnspecified() {
		serverAddr, err := net.ResolveUDPAddr("udp", s.Server)
		if err != nil {
			return nil, fmt.Errorf("resolve udp address %s: %w", s.Server, err)
		}

		remoteAddr.IP = serverAddr.IP
	}

	udpConn := &UDPConn{
		PacketConn: packetConn,
		TCPConn:    conn,
		ServerAddr: remoteAddr,
	}

	if addr != AddrZero {
		connectedAddr, err := addr.UDP()
		if err != nil {
			return nil, err
		}

		udpConn.ConnectedAddr = connectedAddr
	}

	return udpConn, nil
}

func (s *Dialer) negotiate(conn net.Conn) error {
	method := AuthMethodNone
	if s.Username != "" && s.Password != "" {
		method = AuthMethodPassword
	}

	negReq := NewNegotiationRequest([]AuthMethod{method})
	if _, err := negReq.WriteTo(conn); err != nil {
		return err
	}

	negRep, err := NewNegotiationReplyFrom(conn)
	if err != nil {
		return err
	}

	if negRep.Method != method {
		return ErrAuthMethodNotSupported
	}

	if negRep.Method == AuthMethodPassword {
		passReq := NewPasswordNegotiationRequest(s.Username, s.Password)
		if _, err := passReq.WriteTo(conn); err != nil {
			return err
		}

		passRep, err := NewPasswordNegotiationReplyFrom(conn)
		if err != nil {
			return err
		}

		if passRep.Status != PasswordStatusSuccess {
			return ErrPasswordAuth
		}
	}

	return nil
}