@provably-fair/shuffle/dist/index.js

Array shuffling functionality for provably fair games

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.shuffle = undefined;

var _core = require('@provably-fair/core');

function _toConsumableArray(arr) { if (Array.isArray(arr)) { for (var i = 0, arr2 = Array(arr.length); i < arr.length; i++) { arr2[i] = arr[i]; } return arr2; } else { return Array.from(arr); } }

/**
 * Shuffles an array based on the given seeds, using the given HMAC algorithm.
 * @param {[]} arr Array to be shuffled.
 * @param {string} hmacAlgorithm Algorithm used for computing the HMAC of the given seed pair.
 * @param {string|Buffer} secretSeed Secret seed used as HMAC key.
 * @param {string|Buffer} [publicSeed] Public seed used as HMAC data. To prove fairness of random
 * outputs, the hash of `secretSeed` shall be known before revealing `publicSeed`.
 * @param {function} [hmacBufferUIntParser] Function to be used for parsing a UInt from the
 * generated HMAC buffer.
 * @param {function} [fallbackProvider] Function to provide a fallback value in a given range
 * whether no appropriate number can be parsed from the generated HMAC buffer.
 * @returns {[]} A new array instance containing every element of the input.
 */
var shuffle = exports.shuffle = function shuffle(arr, hmacAlgorithm, secretSeed, publicSeed, hmacBufferUIntParser, fallbackProvider) {
  var result = [].concat(_toConsumableArray(arr));

  for (var i = arr.length - 1; i > 0; i -= 1) {
    // Generate a random integer within [0, i]
    var j = (0, _core.randomInt32)(hmacAlgorithm, secretSeed, publicSeed + '-' + i, 0, i + 1, hmacBufferUIntParser, fallbackProvider);

    // Exchange `result[i]` and `result[j]`
    var _ref = [result[j], result[i]];
    result[i] = _ref[0];
    result[j] = _ref[1];
  }

  return result;
};

exports.default = shuffle;
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