package main

import (
	"bufio"
	"flag"
	"fmt"
	"github.com/armon/go-socks5"
	"golang.org/x/net/context"
	"log"
	"net"
	"os"
	"regexp"
	"strconv"
	"strings"
	"time"
)

// GetFdFromConn get net.Conn's file descriptor.
//func GetFdFromConn(l net.Conn) int {
//	v := reflect.ValueOf(l)
//	netFD := reflect.Indirect(reflect.Indirect(v).FieldByName("fd"))
//	fd := int(netFD.FieldByName("sysfd").Int())
//	return fd
//}
//
//func GetFdFromConn(l net.Conn) int {
//	v := reflect.ValueOf(l)
//	netFD := reflect.Indirect(reflect.Indirect(v).FieldByName("fd"))
//	pfd := reflect.Indirect(netFD.FieldByName("pfd"))
//	fd := int(pfd.FieldByName("Sysfd").Int())
//	return fd
//}

// Dialer .
type Dialer struct {
	ifname  string
	laddrIP string
	err     error
	dialer  *net.Dialer
}

// DialFromInterface .
func DialFromInterface(ifaceName string) *Dialer {
	d := &Dialer{ifname: ifaceName}

	// Lookup rquested interface.
	iface, err := net.InterfaceByName(ifaceName)
	if err != nil {
		d.err = err
		return d
	}

	// Pull the addresses.
	addres, err := iface.Addrs()
	if err != nil {
		d.err = err
		return d
	}

	// Look for the first usable address.
	var targetIP string
	for _, addr := range addres {
		ip, _, err := net.ParseCIDR(addr.String())
		if err != nil {
			d.err = err
			return d
		}
		if ip.IsUnspecified() {
			continue
		}
		if ip.To4().Equal(ip) {
			targetIP = ip.String()
			break
		} else {
			targetIP = "[" + ip.String() + "]"
		}
	}
	if targetIP == "" {
		d.err = fmt.Errorf("no ipv4 found for interface")
		return d
	}
	d.laddrIP = targetIP
	return d
}

func (d *Dialer) lookupAddr(network, addr string) (net.Addr, error) {
	if d.err != nil {
		return nil, d.err
	}
	// If no custom dialer specified, use default one.
	if d.dialer == nil {
		d.dialer = &net.Dialer{}
	}

	// Resolve the address.
	switch network {
	case "tcp", "tcp4", "tcp6":
		addr, err := net.ResolveTCPAddr(network, d.laddrIP+":0")
		return addr, err
	case "udp", "udp4", "udp6":
		addr, err := net.ResolveUDPAddr(network, d.laddrIP+":0")
		return addr, err
	default:
		return nil, fmt.Errorf("unkown network")
	}
}

// Dial .
func (d *Dialer) Dial(network, addr string) (net.Conn, error) {
	laddr, err := d.lookupAddr(network, addr)
	if err != nil {
		return nil, err
	}
	d.dialer.LocalAddr = laddr
	conn, err := d.dialer.Dial(network, addr)
	//syscall.BindToDevice(GetFdFromConn(conn), d.ifname)
	return conn, err
}

// DialTimeout .
func (d *Dialer) DialTimeout(network, addr string, timeout time.Duration) (net.Conn, error) {
	laddr, err := d.lookupAddr(network, addr)
	if err != nil {
		return nil, err
	}
	d.dialer.Timeout = timeout
	d.dialer.LocalAddr = laddr
	return d.dialer.Dial(network, addr)
}

// WithDialer .
func (d *Dialer) WithDialer(dialer net.Dialer) *Dialer {
	d.dialer = &dialer
	return d
}

var dialer *Dialer

func dial(ctx context.Context, network, addr string) (net.Conn, error) {
	conn, err := dialer.Dial(network, addr)
	return conn, err
}

func main() {

	var (
		proxyPort      uint
		proxyUser      string
		proxyPassword  string
		proxyUsersFile string
		interfaceName  string
	)

	flag.UintVar(&proxyPort, "port", 1080, "custom port")
	flag.StringVar(&proxyUser, "login", "q", "login name, needs if you are too lazy to creat a file which contains user data")
	flag.StringVar(&proxyPassword, "password", "q", "password, please read about login name")
	flag.StringVar(&proxyUsersFile, "users", "", "a file which include a list of users, in which has set one user per line, every line include USERNAME:PASSWORD separated by colons")
	flag.StringVar(&interfaceName, "iface", "", "run at specific interface")

	flag.Parse()

	//Initialize socks5 config
	socsk5conf := &socks5.Config{
		Logger: log.New(os.Stdout, "", log.LstdFlags),
	}

	if interfaceName != "" {
		dialer = DialFromInterface(interfaceName)
		socsk5conf.Dial = dial
	}

	//creds := socks5.StaticCredentials{
	//	proxyUser: proxyPassword,
	//	"dsa": "dsa",
	//}
	//var creds socks5.CredentialStore

	userData := make(map[string]string)

	if (proxyUser != "") != (proxyPassword != "") {
		log.Fatal("Specify password and login name just together a time")
	}
	if proxyUser != "" && proxyPassword != "" {
		userData[proxyUser] = proxyPassword
	}

	// reads users from file
	if proxyUsersFile != "" {
		file, err := os.Open(proxyUsersFile)
		if err != nil {
			log.Print(err)
			log.Print("I cannot read the file, I ignore it.")
		}

		r := bufio.NewReader(file)
		for {
			line, _, err := r.ReadLine()
			if err != nil {
				break
			}
			data := strings.Split(string(line), ":")
			if len(data) != 2 {
				log.Print("line \"" + string(line) + "\" is invalid")
				break
			}
			correct, err := regexp.MatchString("[A-z0-9_]+", data[0])
			if !correct || err != nil {
				log.Print("error at parsing line: " + string(line))
				break
			}
			correct, err = regexp.MatchString("[A-z0-9_]+", data[1])
			if !correct || err != nil {
				log.Print("error at parsing line: " + string(line))
				break
			}

			// all right
			userData[data[0]] = data[1]
		}
	}

	cator := socks5.UserPassAuthenticator{Credentials: socks5.StaticCredentials(userData)}
	socsk5conf.AuthMethods = []socks5.Authenticator{cator}

	server, err := socks5.New(socsk5conf)
	if err != nil {
		log.Fatal(err)
	}

	log.Printf("Start listening proxy service on port %d\n", proxyPort)
	if err := server.ListenAndServe("tcp", ":"+strconv.Itoa(int(proxyPort))); err != nil {
		log.Fatal(err)
	}
}