// BlockColorChanger.js
// Podbarvuje oranžovou barvou vždy jednu náhodně vybranou položku.
                                                 
function changeColor(id, color1, color2, delay, random) {  

  Array.prototype.shuffle = function() {
  var rnd, tmp, j = this.length;       
    for (j; j>0; j) {
      rnd = parseInt(Math.random()*j);
      tmp = this[--j];
      this[j] = this[rnd]; 
      this[rnd] = tmp;
    };
  return this;  
  };
  
  var elements = new Array();   
  
  for (var i = 0; i < document.getElementById(id).getElementsByTagName("li").length; i++) {
  elements[i] = document.getElementById(id).getElementsByTagName("li")[i];
  }
  
  var index = 0;
  
  function loop() {     
    if(index > elements.length-1 || index <= 0) {
      index = 0;                     
      elements[elements.length-1].style.color = color1;
      if (random) { 
        elements = elements.shuffle(); 
      }
    } else {                           
      elements[index-1].style.color = color1;
    }       
    elements[index++].style.color = color2;
    
    setTimeout(loop,delay);
  };  
  loop();  
};