main.js

// parcel required for these import to work like that
import seedrandom from 'seedrandom';
import bigInt from 'big-integer';

const SALT = 'ds-glasses-app-2019';
const ALPHABET = 'ABCDEFGHIJKLMNPQRSTUVWXYZ1234567890'; // no big O
let INPUT_BASE = 100;

let alphabet = ALPHABET; // shuffled alphabet (according to salt)


function shuffleArray(array, random = Math.random) {
  let m = array.length;
  let t;
  let i;
  while (m) {
    i = Math.floor(random() * m--);
    t = array[m];
    array[m] = array[i];
    array[i] = t;
  }
  return array;
}

function seed(salt) {
  const rng = new seedrandom(salt);
  alphabet = shuffleArray(alphabet.split(''), rng).join('');
}

function base(b) {
  if (b >= 2) {
    INPUT_BASE = b;
  } else {
    throw 'base needs to be >= 2'
  }
}

(function init() {
  seed(SALT);
})();


// convert number system
function cns(fromBase, toBase, inputArray) {
  return bigInt.fromArray(inputArray, fromBase).toArray(toBase).value;
}

// console.log( cns(100, 36, [1, 2, 3, 4, 5,]) );


// make groups of 4 or 3, whichever makes longer last section
function add_dashes(str) {
  let mod4 = str.length % 4;
  let mod3 = str.length % 3;
  if (mod4 == 0 || (mod3 > 0 && mod4 > mod3)) {
    return str.match(/.{1,4}/g).join('-');
  }
  return str.match(/.{1,3}/g).join('-');
}

// checksum = (sum of digits) mod (INPUT_BASE-1) + 1
// range of checksum: [1..INPUT_BASE-1]
// cheksum is added at first position and can't be zero
function checksum(arr) {
  return arr.reduce((acc, x) => acc + x, 0) % (INPUT_BASE-1) + 1;
}

function encode2(arr) {
  // check digits
  for (let d of arr) {
    if (d < 0 || d > INPUT_BASE-1) {
      console.warn(`Digit out of range [0-${INPUT_BASE-1}]:`, d);
      return false;
    }
  }
  // console.log( checksum(arr) );
  arr = arr.slice(); // copy input
  arr.unshift(checksum(arr)); // add checksum

  let enc = cns(INPUT_BASE, alphabet.length, arr);
  let str = enc.map(x => alphabet[x]).join('');
  str = add_dashes(str);
  return str;
}

function hasLowerCase(str) {
  return (/[a-z]/.test(str));
}

function decode2(str) {
  str = str.replace(/-/g, ''); // remove dashes
  if (!hasLowerCase(alphabet)) {  // uppercase (only if alphabet is fully upper case)
    str = str.toUpperCase();
  }
  str = str.replace(/O/, '0'); // replace accidental o's with zeros
  let arr = str.split('').map(x => alphabet.indexOf(x));
  arr = cns(alphabet.length, INPUT_BASE, arr);
  let checkdigit = arr.shift();
  if (checkdigit !== checksum(arr)) {
    console.warn('Checksum mismatch');
    return false;
  }
  return arr;
}

// let c2;
// c2 = encode2([0, 1, 2, 3, 4]);
// console.log( c2 );
// console.log( decode2(c2) );

export {
  encode2 as encode,
  decode2 as decode,
  seed,
  seed as salt,
  base
};