package main

import (
//    "bufio"
    "fmt"
    "log"
    "os"
	"net"
	"strconv"
	"io"
	"context"
	"time"
	"math/rand"
	"bytes"

	"golang.org/x/crypto/ssh"

//	"github.com/songgao/packets/ethernet"
	"github.com/songgao/water"

    "github.com/vishvananda/netlink"
)

type Client struct {
	ifce *water.Interface
	hostname string
	addr *netlink.Addr
	addr_str string
}

// -- funcs --

// writes out desired hostname to file. generates a small bash script for 
// the client to run
//func generateNewClient() {
//
//	var desired_hostname string
//	fmt.Printf("Please enter a desired hostname for the new client: ")
//	
//    scanner := bufio.NewScanner(os.Stdin)
//    scanner.Scan()
//    err := scanner.Err()
//    if err != nil {
//        log.Fatal(err)
//    	panic(err)
//	}
//	desired_hostname = scanner.Text()
//
//	
//}

// maps ip --> hostname
// used to verify collisions
var client_leases = make(map[string]string)

var mode string
func detectMode() {
	mode = os.Getenv("LAZYVPN_MODE")
	if len(mode) == 0 {
		fmt.Println("Mode not set! assuming CLIENT")
		mode = "CLIENT"
	}
	fmt.Printf("Running in mode %s\n", mode)
	return 
}

func generateClientTUN(hn string) Client {

	// configure TUN interface	
	config := water.Config{
		DeviceType: water.TUN,
	}
	config.Name = "tun_"+hn
	

	cl_ifce, err := water.New(config)
	if err != nil {
		log.Fatal(err)
	}

	// Generate a free address to assign
	var cl_Addr_str string
	if mode == "CLIENT" {
		// This is a bad way of doing it, and only accounts for local conflicts
		// theres definitely a way to find if it conflicts somewhere else
		// ideally, it shouldnt be locked to this 16 block, either. eventually,
		// the allowed range (CIDR included) should be defined.
		// this is an alpha for now, just to get *something* nice working	
		r := rand.New(rand.NewSource(255))
		for {
			var b1 int = int(r.Int31n(255))	
			var b2 int = int(r.Int31n(255))
			cl_Addr_str = "." + strconv.Itoa(b1) + "." + strconv.Itoa(b2)

			fmt.Println(cl_Addr_str)

			_, isLeased := client_leases[cl_Addr_str]
			if !isLeased {
				break
			}
		}
	} else {
		// its the server
		cl_Addr_str = ".0.1"
	}

	cl_Link, err := netlink.LinkByName(config.Name)
	if err != nil {
		log.Fatal(err)
	}

	cl_Addr_str = "169.254"+cl_Addr_str
	cl_Addr, err := netlink.ParseAddr(cl_Addr_str+"/16")
	if err != nil {
		log.Fatal(err)
	}
	
	// register addr -> ifce with host
	netlink.AddrAdd(cl_Link, cl_Addr)

	return Client {
		ifce: cl_ifce,
		hostname: hn,
		addr: cl_Addr,
		addr_str: cl_Addr_str,
	}
}

func StartListener(addr string) {
	// listen on port 28173
	l, err := net.Listen("tcp", addr+":28173")
	if err != nil {
		log.Fatal(err)
	}
	defer l.Close()
	
	fmt.Printf("Listening on %s port 28173", addr)

	for {
		// Wait for a connection.
		conn, err := l.Accept()
		if err != nil {
			log.Fatal(err)
		}

		// Handle the connection in a new goroutine.
		// The loop then returns to accepting, so that
		// multiple connections may be served concurrently.
		go func(c net.Conn) {
			// Echo all incoming data.
			io.Copy(c, c)
			// Shut down the connection.
			c.Close()
		}(conn)
	}
}

func StartDialer() {
	var d net.Dialer
	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
	defer cancel()

	fmt.Printf("Attempting autodiscovery")
	conn, err := d.DialContext(ctx, "tcp", "169.254.0.1:28173")
	if err != nil {
		log.Fatalf("Failed to dial: %v", err)
	}
	defer conn.Close()

	if _, err := conn.Write([]byte("Hello, World!")); err != nil {
		log.Fatal(err)
	}
}

func main() {
	// Detect if we are in CLIENT or SERVER mode
	detectMode()
	
	// Zeroth stage - gather info
	var hostKey ssh.PublicKey
	

	config := &ssh.ClientConfig {
		User: os.Getenv("LAZYUSER"),
		Auth: []ssh.authmethod {
			ssh.Password(os.Getenv("LAZYPASS")),
		},
		HostKeyCallback: ssh.FixedHostKey(hostKey),
	}

	// First stage - attempt to connect to public host
	var host string = "192.168.122.1"
	fmt.Printf("Dialing host %s....\n", host)
	client, err := ssh.Dial("tcp", host+":22278", config)
	if err != nil {
		log.Fatal("Failed to dial: ", err)
	}
	defer client.Close()

	// Final stage
	if mode == "SERVER" {
		// open, listen and wait
		StartListener(registered_client.addr_str)
	} else {
		// connect to far end
		StartDialer()
	}
}