'use strict';

var crypto = require('crypto');
var b32 = require('thirty-two');

// Generate a key
function generateOtpKey() {
  // 20 cryptographically random binary bytes (160-bit key)
  var key = crypto.randomBytes(20);

  return key;
}

// Text-encode the key as base32 (in the style of Google Authenticator - same as Facebook, Microsoft, etc)
function encodeGoogleAuthKey(bin) {
  // 32 ascii characters without trailing '='s
  var base32 = b32.encode(bin).toString('utf8').replace(/=/g, '');

  // lowercase with a space every 4 characters
  var key = base32.toLowerCase().replace(/(\w{4})/g, "$1 ").trim();

  return key;
}

function generateGoogleAuthKey() {
  return encodeGoogleAuthKey(generateOtpKey());
}

// Binary-decode the key from base32 (Google Authenticator, FB, M$, etc)
function decodeGoogleAuthKey(key) {
  // decode base32 google auth key to binary
  var unformatted = key.replace(/\W+/g, '').toUpperCase();
  var bin = b32.decode(unformatted);

  return bin;
}

// Generate a Google Auth Token
function generateGoogleAuthToken(key) {
  var bin = decodeGoogleAuthKey(key);
  var notp = require('notp');

  return notp.totp.gen(bin);
}

// Verify a Google Auth Token
function verifyGoogleAuthToken(key, token) {
  var bin = decodeGoogleAuthKey(key);
  var notp = require('notp');

  token = token.replace(/\W+/g, '');

  // window is +/- 1 period of 30 seconds
  return notp.totp.verify(token, bin, { window: 1, time: 30 });
}

module.exports.generateKey = generateGoogleAuthKey;
module.exports.generateToken = generateGoogleAuthToken;
module.exports.verifyToken = verifyGoogleAuthToken;
module.exports.generateTotpUri = function (secret, accountName, issuer, algo, digits, period) {
  // Full OTPAUTH URI spec as explained at
  // https://github.com/google/google-authenticator/wiki/Key-Uri-Format
  return 'otpauth://totp/'
    + encodeURI(issuer || '') + ':' + encodeURI(accountName || '')
    + '?secret=' + secret.replace(/[\s\.\_\-]+/g, '').toUpperCase()
    + '&issuer=' + encodeURIComponent(issuer || '')
    + '&algorithm=' + (algo || 'SHA1')
    + '&digits=' + (digits || 6)
    + '&period=' + (period || 30)
    ;  
};