package main

import (
	"crypto/sha1"
	"io"
	"log"
	"math/rand"
	"net"
	"os"
	"time"

	"golang.org/x/crypto/pbkdf2"

	"github.com/klauspost/compress/snappy"
	"github.com/urfave/cli"
	kcp "github.com/xtaci/kcp-go"
	"github.com/xtaci/smux"
)

var (
	// VERSION is injected by buildflags
	VERSION = "SELFBUILD"
	// SALT is use for pbkdf2 key expansion
	SALT = "kcp-go"
)

type compStream struct {
	conn net.Conn
	w    *snappy.Writer
	r    *snappy.Reader
}

func (c *compStream) Read(p []byte) (n int, err error) {
	return c.r.Read(p)
}

func (c *compStream) Write(p []byte) (n int, err error) {
	n, err = c.w.Write(p)
	err = c.w.Flush()
	return n, err
}

func (c *compStream) Close() error {
	return c.conn.Close()
}

func newCompStream(conn net.Conn) *compStream {
	c := new(compStream)
	c.conn = conn
	c.w = snappy.NewBufferedWriter(conn)
	c.r = snappy.NewReader(conn)
	return c
}

// handle multiplex-ed connection
func handleMux(conn io.ReadWriteCloser, config *Config) {
	// stream multiplex
	smuxConfig := smux.DefaultConfig()
	smuxConfig.MaxReceiveBuffer = config.SockBuf
	mux, err := smux.Server(conn, smuxConfig)
	if err != nil {
		log.Println(err)
		return
	}
	defer mux.Close()
	for {
		p1, err := mux.AcceptStream()
		if err != nil {
			log.Println(err)
			return
		}
		p2, err := net.DialTimeout("tcp", config.Target, 5*time.Second)
		if err != nil {
			p1.Close()
			log.Println(err)
			continue
		}
		if err := p2.(*net.TCPConn).SetReadBuffer(config.SockBuf); err != nil {
			log.Println("TCP SetReadBuffer:", err)
		}
		if err := p2.(*net.TCPConn).SetWriteBuffer(config.SockBuf); err != nil {
			log.Println("TCP SetWriteBuffer:", err)
		}
		go handleClient(p1, p2)
	}
}

func handleClient(p1, p2 io.ReadWriteCloser) {
	log.Println("stream opened")
	defer log.Println("stream closed")
	defer p1.Close()
	defer p2.Close()

	// start tunnel
	p1die := make(chan struct{})
	go func() { io.Copy(p1, p2); close(p1die) }()

	p2die := make(chan struct{})
	go func() { io.Copy(p2, p1); close(p2die) }()

	// wait for tunnel termination
	select {
	case <-p1die:
	case <-p2die:
	}
}

func checkError(err error) {
	if err != nil {
		log.Printf("%+v\n", err)
		os.Exit(-1)
	}
}

func main() {
	rand.Seed(int64(time.Now().Nanosecond()))
	if VERSION == "SELFBUILD" {
		// add more log flags for debugging
		log.SetFlags(log.LstdFlags | log.Lshortfile)
	}
	myApp := cli.NewApp()
	myApp.Name = "kcptun"
	myApp.Usage = "server(with SMUX)"
	myApp.Version = VERSION
	myApp.Flags = []cli.Flag{
		cli.StringFlag{
			Name:  "listen,l",
			Value: ":29900",
			Usage: "kcp server listen address",
		},
		cli.StringFlag{
			Name:  "target, t",
			Value: "127.0.0.1:12948",
			Usage: "target server address",
		},
		cli.StringFlag{
			Name:   "key",
			Value:  "it's a secrect",
			Usage:  "pre-shared secret between client and server",
			EnvVar: "KCPTUN_KEY",
		},
		cli.StringFlag{
			Name:  "crypt",
			Value: "aes",
			Usage: "aes, aes-128, aes-192, salsa20, blowfish, twofish, cast5, 3des, tea, xtea, xor, none",
		},
		cli.StringFlag{
			Name:  "mode",
			Value: "fast",
			Usage: "profiles: fast3, fast2, fast, normal",
		},
		cli.IntFlag{
			Name:  "mtu",
			Value: 1350,
			Usage: "set maximum transmission unit for UDP packets",
		},
		cli.IntFlag{
			Name:  "sndwnd",
			Value: 1024,
			Usage: "set send window size(num of packets)",
		},
		cli.IntFlag{
			Name:  "rcvwnd",
			Value: 1024,
			Usage: "set receive window size(num of packets)",
		},
		cli.IntFlag{
			Name:  "datashard",
			Value: 10,
			Usage: "set reed-solomon erasure coding - datashard",
		},
		cli.IntFlag{
			Name:  "parityshard",
			Value: 3,
			Usage: "set reed-solomon erasure coding - parityshard",
		},
		cli.IntFlag{
			Name:  "dscp",
			Value: 0,
			Usage: "set DSCP(6bit)",
		},
		cli.BoolFlag{
			Name:  "nocomp",
			Usage: "disable compression",
		},
		cli.BoolFlag{
			Name:   "acknodelay",
			Usage:  "flush ack immediately when a packet is received",
			Hidden: true,
		},
		cli.IntFlag{
			Name:   "nodelay",
			Value:  0,
			Hidden: true,
		},
		cli.IntFlag{
			Name:   "interval",
			Value:  40,
			Hidden: true,
		},
		cli.IntFlag{
			Name:   "resend",
			Value:  0,
			Hidden: true,
		},
		cli.IntFlag{
			Name:   "nc",
			Value:  0,
			Hidden: true,
		},
		cli.IntFlag{
			Name:   "sockbuf",
			Value:  4194304, // socket buffer size in bytes
			Hidden: true,
		},
		cli.IntFlag{
			Name:   "keepalive",
			Value:  10, // nat keepalive interval in seconds
			Hidden: true,
		},
		cli.StringFlag{
			Name:  "log",
			Value: "",
			Usage: "specify a log file to output, default goes to stderr",
		},
		cli.StringFlag{
			Name:  "c",
			Value: "", // when the value is not empty, the config path must exists
			Usage: "config from json file, which will override the command from shell",
		},
	}
	myApp.Action = func(c *cli.Context) error {
		config := Config{}
		config.Listen = c.String("listen")
		config.Target = c.String("target")
		config.Key = c.String("key")
		config.Crypt = c.String("crypt")
		config.Mode = c.String("mode")
		config.MTU = c.Int("mtu")
		config.SndWnd = c.Int("sndwnd")
		config.RcvWnd = c.Int("rcvwnd")
		config.DataShard = c.Int("datashard")
		config.ParityShard = c.Int("parityshard")
		config.DSCP = c.Int("dscp")
		config.NoComp = c.Bool("nocomp")
		config.AckNodelay = c.Bool("acknodelay")
		config.NoDelay = c.Int("nodelay")
		config.Interval = c.Int("interval")
		config.Resend = c.Int("resend")
		config.NoCongestion = c.Int("nc")
		config.SockBuf = c.Int("sockbuf")
		config.KeepAlive = c.Int("keepalive")
		config.Log = c.String("log")

		if c.String("c") != "" {
			//Now only support json config file
			err := parseJSONConfig(&config, c.String("c"))
			checkError(err)
		}

		// log redirect
		if config.Log != "" {
			f, err := os.OpenFile(config.Log, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
			checkError(err)
			defer f.Close()
			log.SetOutput(f)
		}

		switch config.Mode {
		case "normal":
			config.NoDelay, config.Interval, config.Resend, config.NoCongestion = 0, 30, 2, 1
		case "fast":
			config.NoDelay, config.Interval, config.Resend, config.NoCongestion = 0, 20, 2, 1
		case "fast2":
			config.NoDelay, config.Interval, config.Resend, config.NoCongestion = 1, 20, 2, 1
		case "fast3":
			config.NoDelay, config.Interval, config.Resend, config.NoCongestion = 1, 10, 2, 1
		}

		log.Println("version:", VERSION)
		pass := pbkdf2.Key([]byte(config.Key), []byte(SALT), 4096, 32, sha1.New)
		var block kcp.BlockCrypt
		switch config.Crypt {
		case "tea":
			block, _ = kcp.NewTEABlockCrypt(pass[:16])
		case "xor":
			block, _ = kcp.NewSimpleXORBlockCrypt(pass)
		case "none":
			block, _ = kcp.NewNoneBlockCrypt(pass)
		case "aes-128":
			block, _ = kcp.NewAESBlockCrypt(pass[:16])
		case "aes-192":
			block, _ = kcp.NewAESBlockCrypt(pass[:24])
		case "blowfish":
			block, _ = kcp.NewBlowfishBlockCrypt(pass)
		case "twofish":
			block, _ = kcp.NewTwofishBlockCrypt(pass)
		case "cast5":
			block, _ = kcp.NewCast5BlockCrypt(pass[:16])
		case "3des":
			block, _ = kcp.NewTripleDESBlockCrypt(pass[:24])
		case "xtea":
			block, _ = kcp.NewXTEABlockCrypt(pass[:16])
		case "salsa20":
			block, _ = kcp.NewSalsa20BlockCrypt(pass)
		default:
			config.Crypt = "aes"
			block, _ = kcp.NewAESBlockCrypt(pass)
		}

		lis, err := kcp.ListenWithOptions(config.Listen, block, config.DataShard, config.ParityShard)
		checkError(err)
		log.Println("listening on:", lis.Addr())
		log.Println("target:", config.Target)
		log.Println("encryption:", config.Crypt)
		log.Println("nodelay parameters:", config.NoDelay, config.Interval, config.Resend, config.NoCongestion)
		log.Println("sndwnd:", config.SndWnd, "rcvwnd:", config.RcvWnd)
		log.Println("compression:", !config.NoComp)
		log.Println("mtu:", config.MTU)
		log.Println("datashard:", config.DataShard, "parityshard:", config.ParityShard)
		log.Println("acknodelay:", config.AckNodelay)
		log.Println("dscp:", config.DSCP)
		log.Println("sockbuf:", config.SockBuf)
		log.Println("keepalive:", config.KeepAlive)

		if err := lis.SetDSCP(config.DSCP); err != nil {
			log.Println("SetDSCP:", err)
		}
		if err := lis.SetReadBuffer(config.SockBuf); err != nil {
			log.Println("SetReadBuffer:", err)
		}
		if err := lis.SetWriteBuffer(config.SockBuf); err != nil {
			log.Println("SetWriteBuffer:", err)
		}
		for {
			if conn, err := lis.AcceptKCP(); err == nil {
				log.Println("remote address:", conn.RemoteAddr())
				conn.SetStreamMode(true)
				conn.SetNoDelay(config.NoDelay, config.Interval, config.Resend, config.NoCongestion)
				conn.SetMtu(config.MTU)
				conn.SetWindowSize(config.SndWnd, config.RcvWnd)
				conn.SetACKNoDelay(config.AckNodelay)
				conn.SetKeepAlive(config.KeepAlive)

				if config.NoComp {
					go handleMux(conn, &config)
				} else {
					go handleMux(newCompStream(conn), &config)
				}
			} else {
				log.Printf("%+v", err)
			}
		}
	}
	myApp.Run(os.Args)
}