/**
 * @author mrdoob / http://mrdoob.com/
 * @author jetienne / http://jetienne.com/
 * @author paulirish / http://paulirish.com/
 */
var MemoryStats = function () {
  var msMin = 100;
  var msMax = 0;

  var container = document.createElement('div');
  container.id = 'stats';
  container.style.cssText = 'width:80px;opacity:0.9;cursor:pointer';

  var msDiv = document.createElement('div');
  msDiv.id = 'ms';
  msDiv.style.cssText = 'padding:0 0 3px 3px;text-align:left;background-color:#020;';
  container.appendChild(msDiv);

  var msText = document.createElement('div');
  msText.id = 'msText';
  msText.style.cssText = 'color:#0f0;font-family:Helvetica,Arial,sans-serif;font-size:9px;font-weight:bold;line-height:15px';
  msText.innerHTML = 'Memory';
  msDiv.appendChild(msText);

  var msGraph = document.createElement('div');
  msGraph.id = 'msGraph';
  msGraph.style.cssText = 'position:relative;width:74px;height:30px;background-color:#0f0';
  msDiv.appendChild(msGraph);

  while (msGraph.children.length < 74) {
    var bar = document.createElement('span');
    bar.style.cssText = 'width:1px;height:30px;float:left;background-color:#131';
    msGraph.appendChild(bar);
  }

  var updateGraph = function (dom, height, color) {
    var child = dom.appendChild(dom.firstChild);
    child.style.height = height + 'px';
    if (color) child.style.backgroundColor = color;
  };

  var perf = window.performance || {};
  // polyfill usedJSHeapSize
  if (!perf && !perf.memory) {
    perf.memory = { usedJSHeapSize: 0 };
  }
  if (perf && !perf.memory) {
    perf.memory = { usedJSHeapSize: 0 };
  }

  // support of the API?
  if (perf.memory.totalJSHeapSize === 0) {
    console.warn('totalJSHeapSize === 0... performance.memory is only available in Chrome .');
  }

  // TODO, add a sanity check to see if values are bucketed.
  // If so, reminde user to adopt the --enable-precise-memory-info flag.
  // open -a "/Applications/Google Chrome.app" --args --enable-precise-memory-info

  var lastTime = Date.now();
  var lastUsedHeap = perf.memory.usedJSHeapSize;
  return {
    domElement: container,

    update: function () {
      // refresh only 30time per second
      if (Date.now() - lastTime < 1000 / 30) return;
      lastTime = Date.now();

      var delta = perf.memory.usedJSHeapSize - lastUsedHeap;
      lastUsedHeap = perf.memory.usedJSHeapSize;
      var color = delta < 0 ? '#830' : '#131';

      var ms = perf.memory.usedJSHeapSize;
      msMin = Math.min(msMin, ms);
      msMax = Math.max(msMax, ms);
      msText.textContent = 'Mem: ' + bytesToSize(ms, 2);

      var normValue = ms / (30 * 1024 * 1024);
      var height = Math.min(30, 30 - normValue * 30);
      updateGraph(msGraph, height, color);

      function bytesToSize(bytes, nFractDigit) {
        var sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
        if (bytes == 0) return 'n/a';
        nFractDigit = nFractDigit !== undefined ? nFractDigit : 0;
        var precision = Math.pow(10, nFractDigit);
        var i = Math.floor(Math.log(bytes) / Math.log(1024));
        return Math.round((bytes * precision) / Math.pow(1024, i)) / precision + ' ' + sizes[i];
      }
    },
  };
};

(function () {
  var stats = new MemoryStats();
  stats.domElement.style.position = 'fixed';
  stats.domElement.style.right = '0px';
  stats.domElement.style.bottom = '0px';
  document.body.appendChild(stats.domElement);
  requestAnimationFrame(function rAFloop() {
    stats.update();
    requestAnimationFrame(rAFloop);
  });

  return {
    memoryStats: stats,
    renderRate: renderRate,
  };
})();
