Random pairs generation

races.js

// sortedHashes = ['a', 'b', 'c', 'd', 'e', ...]
// doneRaces = [['a', 'c'], ['c', 'e'], ['a', 'b'], ...]
function getNewVoteRace(sortedHashes, doneRaces) {
  let firstHash;

  let secondIdxMax;
  let secondTotalOpts;
  let secondBlacklist;

  while(_.isNil(secondIdxMax) || secondBlacklist.length >= secondTotalOpts) {
    const firstIdxMax = sortedHashes.length - 2;
    const firstIdxRand = getRandomInt(firstIdxMax);
    const firstIdx = firstIdxRand;

    firstHash = sortedHashes[firstIdx];

    secondIdxMax = sortedHashes.length - 1 - firstIdx - 1;

    secondTotalOpts = secondIdxMax + 1;
    secondBlacklist = doneRaces
      .filter(([f,s]) => f === firstHash)
      .map(([f,s]) => s);
  }

  let secondHash;
  while(_.isNil(secondHash) || secondBlacklist.indexOf(secondHash) !== -1) {
    const secondIdxRand = getRandomInt(secondIdxMax);
    const secondIdx = sortedHashes.length - 1 - secondIdxRand;
    secondHash = sortedHashes[secondIdx];
  }

  return [firstHash, secondHash];
}