var minItemNumber = 1;
var maxItemNumber = 5;
var itemWidth = 144;

var currentItem = minItemNumber;

function rotateItems() {
  currentItem++;

  if(currentItem > maxItemNumber)
    currentItem = minItemNumber;

  showItem(currentItem);
}

function scrollArrow(direction) {
  switch(direction) {
    case 'previous':
      showItem(correctItemRange(--currentItem));
      break;
    case 'next':
      showItem(correctItemRange(++currentItem));
      break;
  }
}

function correctItemRange(value) {
  if(value > maxItemNumber)
    value = minItemNumber;
  else if (value < minItemNumber)
    value = maxItemNumber;

  return value;
}

function showItem(itemIndex) {
  currentItem = itemIndex;
  new Effect.Move("sliding_items", { x: -itemWidth * (currentItem - 1), y: 0, mode: 'absolute', duration: 0.4 });

  for(var i = 1; i <= maxItemNumber; i++)
    $("p" + i + "-tab").className = "inactive";
  $("p" + currentItem + "-tab").className = "active";
}

new PeriodicalExecuter(function() { rotateItems(); }, 5);