Click anywhere on the webpage to gacha :)

click-anywhere-gacha.js

// Click-to-Gacha easter egg module for web pages
// (C) Jeremy Lam 2017.
// Require RandomJs and FingerPrintJs2 module in order to work
// You can change the behaviour in 'setTitle' and 'notify' function.

(function (root, factory) {
  if(typeof define === 'function' && define.amd)
    define(['random', 'fingerprintjs2'], factory);
  else if(typeof module === 'object' && module.exports)
    factory(require('random-js'), require('fingerprintjs2'));
  else
    factory(root.Random, root.Fingerprint2);
}(this, function(Random, Fingerprint2) {
  'use strict';
  var maxInt = Number.MAX_SAFE_INTEGER;
  var body = document.body;
  var ls = (function(localStorage) {
    var test = '__ls_testing__';
    try {
      localStorage.setItem(test, test);
      localStorage.removeItem(test);
      return localStorage;
    } catch(e) {
      console.warn('Detected your browser does not support localStorage.\nGacha results will not be saved.');
      return null;
    }
  })(window.localStorage);
  var log10 = Math.log10 || function(v) {
    return Math.log(v) * Math.LOG10E;
  };
  
  // Called when clicked somewhere to gacha
  function setTitle(text) {
    document.title = text;
  }
  
  // Called when get something special in gacha
  function notify(text) {
    alert('Congrats! You got a ' + text + ' card!');
  }
  
  function mdbLookup(x, y) {
    if(!(x >= 0 && y >= 0))
      return 0;
    x = ~~x;
    y = ~~y;
    var r = 0;
    for(var m = 1, o = 0; (x >= m || y >= m) && m < maxInt; m <<= 1)
      r |= (x & m) << o++ | (y & m) << o;
    return r;
  }

  function mdbMaxValue(x, y) {
    x = Math.min(x, y) + 1;
    x |= x >> 0x01;
    x |= x >> 0x02;
    x |= x >> 0x04;
    x |= x >> 0x08;
    x |= x >> 0x10;
    return (x + 1) >> 1;
  }

  function getDiffPerUnit(w, h) {
    var s = mdbMaxValue(w, h);
    return 1 / mdbLookup(s - 1, s - 1);
  }

  function getMdbValue(x, y, w, h) {
    var s = mdbMaxValue(w, h);
    return mdbLookup(x / w * s,  y / h * s) / mdbLookup(s - 1, s - 1);
  }
  
  var hs, isHsReady = false, lastTimeHash, rndEngine, rnd, refValue;
  var cards = ls && ls.getItem('rare');
  cards = cards ? JSON.parse(cards) : [
    { text: '-', count: 0, chance: 0 },
    { text: 'N', count: 0 },
    { text: 'R', count: 0 },
    { text: 'SR', count: 0 },
    { text: 'SSR', count: 0 },
    { text: 'UR', count: 0 },
    { text: 'LR', count: 0 },
    { text: 'HR', count: 0 }
  ];

  new Fingerprint2().get(function(result) {
    hs = Number.parseInt(result.substr(0, 12), 16);
    isHsReady = true;
  });
  
  function getTimeHash() {
    return Math.floor(Date.now() / 86400000);
  }
  
  function seed() {
    if(!rndEngine) rndEngine = Random.engines.mt19937();
    rndEngine.seedWithArray([hs, lastTimeHash = getTimeHash(), cards[0].chance || 0]);
    if(!rnd) rnd = new Random(rndEngine);
    refValue = rnd.real(0, 1);
  }
  
  body.addEventListener('click', function(e) {
    if(!isHsReady) return;
    if(getTimeHash() !== lastTimeHash) seed();
    var w = body.clientWidth, h = body.clientHeight;
    var deltaRange = getDiffPerUnit(w, h) / 2;
    var rare = Math.max(
      Math.min(
        -Math.floor(
          log10(
            Math.abs(
              getMdbValue(e.pageX, e.pageY, w, h)
              + rnd.real(-deltaRange, deltaRange)
              - refValue
            )
          )
        ), cards.length - 1
      ), 0
    );
    cards[rare].count++;
    if(rare > 2) {
      notify(cards[rare].text);
      cards[0].chance = rnd.integer(0, maxInt);
      seed();
    }
    var disp = '';
    for(var i = cards.length - 1; i > 0; i--) {
      if(cards[i].count < 1) continue;
      if(disp.length) disp += ', ';
      disp += cards[i].text + 'x' + cards[i].count;
    }
    setTitle(disp);
    if(ls) ls.setItem('rare', JSON.stringify(cards));
  });
}));