/**

* @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;

}

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

// support of the API?
if( performance.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= performance.memory.usedJSHeapSize;
return {
  domElement: container,

  update: function () {

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

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

    var ms  = performance.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];
    };
  }

}

};