hashChain.js

const assert = require("assert");
const { v4: uuid } = require("uuid");
const { sha256 } = require("./utils");

// generate a provable hash chain count to -1
function generateHashChain(count, seed) {
  assert(seed, "requires seed");
  assert(seed, "requires count");

  var result = Array(count);

  // generate chain in revese order
  for (var i = count - 1; i >= 0; i--) {
    seed = sha256(seed);
    result[i] = seed;
  }

  return result;
}

// manages generating and itteratng through a provable hashchain
// the last hash of the previous chain will be used to generate the next.
function HashChain({ seed = uuid(), count = 1000000, index = 0 }) {
  assert(count >= 1, "requires count");
  assert(seed, "requires seed");

  const chain = generateHashChain(count, seed);

  function state() {
    return { count, seed, index };
  }

  function peek() {
    return chain[index + 1];
  }

  function get() {
    return chain[index];
  }

  function next() {
    const hash = peek();
    assert(hash, "chain has ended");

    // increment index and return hash
    return {
      hash,
      count,
      index: ++index,
    };
  }

  function last() {
    return chain[index - 1];
  }

  return {
    state,
    peek,
    get,
    next,
    last,
  };
}

module.exports = HashChain;