package main

import (
	"errors"
	"fmt"
	"net"
	"os"
	"os/exec"
	"regexp"
)

func checkArg(args []string, pos int, value string) {
	if args[pos] != value {
		fmt.Println(errors.New("invalid command : " + args[pos]))
		os.Exit(10 + pos)
	}
}

func main() {
	if len(os.Args) != 6 {
		fmt.Println(errors.New("missing args"), len(os.Args))
		os.Exit(1)
	}

	args := os.Args[1:]

	r := regexp.MustCompile("[^a-zA-Z0-9.-]")
	var ip string

	checkArg(args, 0, "route")
	checkArg(args, 1, "replace")

	if testip := net.ParseIP(args[2]); testip != nil {
		ip = testip.String()
	} else {
		fmt.Println(errors.New("invalid ip"))
		os.Exit(2)
	}

	checkArg(args, 3, "dev")

	dev := r.ReplaceAllString(args[4], "")

	cmd := exec.Command("/bin/ip", "route", "replace", ip, "dev", dev)
	if err := cmd.Run(); err != nil {
		fmt.Println(err)
		os.Exit(3)
	}
}