Jackpot

jackpot.js

const SymbolKeys = {
  Bitcoin: 'bitcoin',
  Cash: 'cash',
  Cherry: 'cherry',
  Diamond: 'diamond',
  Gold: 'gold',
};

// If all rollers equal one of the `Prize` keys, we'll multiply the value by
// the amount the user entered
const Prize = {
  [SymbolKeys.Bitcoin]: 100,
  [SymbolKeys.Cash]: 30,
  [SymbolKeys.Cherry]: 10,
  [SymbolKeys.Diamond]: 75,
  [SymbolKeys.Gold]: 50,
};

const Probabilities = {
  [SymbolKeys.Bitcoin]: 0.05,
  [SymbolKeys.Cash]: 0.25,
  [SymbolKeys.Cherry]: 0.35,
  [SymbolKeys.Diamond]: 0.15,
  [SymbolKeys.Gold]: 0.2,
}

const getRandomWithProbability = (probabilities) => {
  // Generate a random fp number between 0 and 1 exclusive
  const randomNumber = Math.random();

  let acc = 0;

  // Convert `probabilities` to a 2D array where each nested array contains
  // a value and probability e.g., [['bitcoin', 0.05], ['cash', 0.25], ...]
  for (const [value, probability] of Object.entries(probabilities)) {
    // On each iteration we're adding the `probability` to an accumulator
    acc += probability;

    // If the accumulator is less than the random number we previously
    // generated, return the current `value`
    if (randomNumber < acc) {
      return value;
    }
  }

  return null;
}

const spin = (amount) => {
  // Convert `Keys` to array of its values
  const roller = Object.values(SymbolKeys);


  const r1 = getRandomWithProbability(Probabilities);
  const r2 = getRandomWithProbability(Probabilities);
  const r3 = getRandomWithProbability(Probabilities);

  const result = [
    roller[roller.indexOf(r1)],
    roller[roller.indexOf(r2)],
    roller[roller.indexOf(r3)],
  ];

  // Sets let you store unique values. If we have three of the same symbol in
  // `result`, `set` size will be 1 indicating a JACKPOT
  const set = new Set(result);

  if (set.size === 1) {
    let winningSymbol;

    roller.some((item) => {
      if (set.has(item)) {
        winningSymbol = item;

        return true;
      } 

      return false;
    })

    return {
      prize: Prize[winningSymbol] * amount,
      result,
    }
  } 

  return {
    prize: null,
    result,
  }

}

console.log(spin(100));