Potluck Winner calculation logic

find.winner.js

const isaac = require('isaac'); // https://github.com/rubycon/isaac.js
/**
 * generate a random number using isaac RNG
 * @param {String} seed - the seed for isaac RNG
 * @returns {Number} Random number between 0.0 and 1.0
*/
function isaacRandom(seed) {
  isaac.seed(seed);
  return isaac.random();
}

/**
 * find the winner.
 * @param {String} serverSeed - the server seed for current game
 * @param {String} clientSeed
 * @param {Number} totalTicketsWithoutLastBet - Number of tickets issued for this game excluding the last bet.
 * @returns {Object} the user object for winner
*/
function findWinningTicket(serverSeed, clientSeed, totalTicketsWithoutLastBet) {
  // The last bet is excluded from the calculation of `rngSeed` to make it difficult for the operators to change the game outcome in their favor. 
  const rngSeed = createHMACHash(serverSeed, `${clientSeed}-${totalTicketsWithoutLastBet}`);
  const luckyFraction = isaacRandom(rngSeed);
  let winningTicket;
  winningTicket = Math.floor(totalTickets * luckyFraction);
  return findOwnerOfTicket(winningTicket); // find the owner of this ticket from database.
}