var Sticky = function(selector, containerSelector) {
  var element = document.querySelector(selector),
      containerElement = document.querySelector(containerSelector),

      elementTop = parseInt(window.getComputedStyle(element, null).marginTop),

      stickedClass = 'sticked',
      grabEndClass = 'grab-end',

      elementStart, containerElementFinish;

  if (!canSticky) {
    return;
  }

  setPoints();

  window.addEventListener('scroll', function() {
    if (window.scrollY >= elementStart && window.scrollY < containerElementFinish) {
      sticky();
    } else if (window.scrollY >= containerElementFinish) {
      grabEnd();
    } else {
      reset();
    }
  });

  // Private
  function offset(element) {
    var rectangle = element.getBoundingClientRect();

    return {
      top: rectangle.top + document.body.scrollTop,
      left: rectangle.left + document.body.scrollLeft
    }
  }

  function canSticky() {
    if (!element && !containerElement) {
      return false;
    }

    if (window.innerHeight <= 710 || window.innerWidth <= 768) {
      return false;
    }

    return true;
  }


  // Public
  function reset() {
    element.classList.remove(stickedClass, grabEndClass);
    setPoints();
  }

  function sticky() {
    element.classList.remove(grabEndClass);
    element.classList.add(stickedClass);
  }

  function grabEnd() {
    element.classList.remove(stickedClass);
    element.classList.add(grabEndClass);
  }

  function setPoints() {
    elementStart = offset(element).top - elementTop;
    containerElementFinish = offset(containerElement).top + containerElement.offsetHeight - element.offsetHeight - elementTop;
  }

  return {
    reset: reset,
    sticky: sticky,
    grabEnd: grabEnd,
    setPoints: setPoints
  };
};