package main

import (
	"crypto/hmac"
	"crypto/sha1"
	"encoding/base32"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"math/big"
	"os/user"
	"path"
	"strings"
	"time"
)

func TimeStamp() (int64, int) {
        time := time.Now().Unix()
	return time / 30, int(time % 30);
}

func AuthCode(sec string, ts int64) (string, error) {
	normalizedSec := strings.ToUpper(strings.Replace(sec, " ", "", -1))
	key, err := base32.StdEncoding.DecodeString(normalizedSec)
	if err != nil {
		return "", err
	}
	enc := hmac.New(sha1.New, key)
	msg := make([]byte, 8, 8)
	msg[0] = (byte)(ts >> (7 * 8) & 0xff)
	msg[1] = (byte)(ts >> (6 * 8) & 0xff)
	msg[2] = (byte)(ts >> (5 * 8) & 0xff)
	msg[3] = (byte)(ts >> (4 * 8) & 0xff)
	msg[4] = (byte)(ts >> (3 * 8) & 0xff)
	msg[5] = (byte)(ts >> (2 * 8) & 0xff)
	msg[6] = (byte)(ts >> (1 * 8) & 0xff)
	msg[7] = (byte)(ts >> (0 * 8) & 0xff)
	if _, err := enc.Write(msg); err != nil {
		return "", err
	}
	hash := enc.Sum(nil)
	offset := hash[19] & 0x0f
	trunc := hash[offset : offset+4]
	trunc[0] &= 0x7F
	res := new(big.Int).Mod(new(big.Int).SetBytes(trunc), big.NewInt(1000000))
	return fmt.Sprintf("%06d", res), nil
}

func authCodeOrDie(sec string, ts int64) string {
	str, e := AuthCode(sec, ts)
	if e != nil {
		log.Fatal(e)
	}
	return str
}

func main() {
	user, e := user.Current()
	if e != nil {
		log.Fatal(e)
	}
	cfg_path := path.Join(user.HomeDir, ".config/gauth.json")

	conf_content, e := ioutil.ReadFile(cfg_path)
	if e != nil {
		log.Fatal(e)
	}

	var cfg map[string]string
	e = json.Unmarshal(conf_content, &cfg)
	if e != nil {
		log.Fatal(e)
	}

	currentTS, progress := TimeStamp()
	prevTS := currentTS - 1
	nextTS := currentTS + 1

        fmt.Println("           prev   curr   next");
	for name, secret := range cfg {
		prevToken := authCodeOrDie(secret, prevTS)
		currentToken := authCodeOrDie(secret, currentTS)
		nextToken := authCodeOrDie(secret, nextTS)
		fmt.Printf("%-10s %s %s %s\n", name, prevToken, currentToken, nextToken)
	}
        fmt.Printf("[%-29s]\n", strings.Repeat("=", progress));
}