Script used for revealing mystery cards from a block hash

index.js

const RNG = require('rng-js');

const COMMON = 21;
const UNCOMMON = 22;
const RARE = 23;
const MYTHIC = 24;

function shuffle(array, rng) {
  let m = array.length, t, i;

  // While there remain elements to shuffle…
  while (m) {
    // Pick a remaining element…
    i = Math.floor(rng.uniform() * m--);

    // And swap it with the current element.
    t = array[m];
    array[m] = array[i];
    array[i] = t;
  }

  return array;
}

function generate(blockHash) {
  const all = [
    ...Array(777).fill(COMMON),
    ...Array(72).fill(UNCOMMON),
    ...Array(36).fill(RARE),
    ...Array(3).fill(MYTHIC),
  ];
    
  const rng = new RNG(blockHash);
  return shuffle(all, rng);
}

async function main() {
  const blockHash = process.env.BLOCK_HASH;
  if (!blockHash) {
    console.log('BLOCK_HASH required');
    process.exit(1);
  }

  const models = generate(blockHash);
  console.log(JSON.stringify(models));
}

module.exports = (callback) => main().then(() => callback()).catch(callback);

main();