(function runGallery() {
  let index = 0;
  let carousel = document.getElementById("carousel");
  if (!carousel) return; 
  let children = carousel.children;
  let noChildren = children.length;
  if (noChildren < 4) return;
  
  addClasses(index);

  setInterval(rotate, 10000);

  function rotate() {
    removeClasses(index);
    index = ++index % noChildren;
    addClasses(index);
  }

  function removeClasses(index) {
  	children[getIndex(index - 2)].classList.remove("vanish");
    children[getIndex(index - 1)].classList.remove("pre");
    children[getIndex(index)].classList.remove("main");
    children[getIndex(index + 1)].classList.remove("post");
  }

  function addClasses(index) {
  	children[getIndex(index - 2)].classList.add("vanish");
    children[getIndex(index - 1)].classList.add("pre");
    children[getIndex(index)].classList.add("main");
    children[getIndex(index + 1)].classList.add("post");
  }

  function getIndex(rawIndex) {
    if (rawIndex < 0) {
      return noChildren + rawIndex;
    } else {
      return rawIndex % noChildren;
    }
  }
}());