/**
 * author Christopher Blum
 *    - based on the idea of Remy Sharp, http://remysharp.com/2009/01/26/element-in-view-event-plugin/
 *    - forked from http://github.com/zuk/jquery.inview/
 */
(function ($) {
	var inviewObjects = {}, viewportSize, viewportOffset,
		d = document, w = window, documentElement = d.documentElement, expando = $.expando;

	$.event.special.inview = {
		add: function(data) {
			inviewObjects[data.guid + "-" + this[expando]] = { data: data, $element: $(this) };
		},

		remove: function(data) {
			try { delete inviewObjects[data.guid + "-" + this[expando]]; } catch(e) {}
		}
	};

	function getViewportSize() {
		var mode, domObject, size = { height: w.innerHeight, width: w.innerWidth };

		// if this is correct then return it. iPad has compat Mode, so will
		// go into check clientHeight/clientWidth (which has the wrong value).
		if (!size.height) {
			mode = d.compatMode;
			if (mode || !$.support.boxModel) { // IE, Gecko
				domObject = mode === 'CSS1Compat' ?
					documentElement : // Standards
					d.body; // Quirks
				size = {
					height: domObject.clientHeight,
					width:  domObject.clientWidth
				};
			}
		}

		return size;
	}

	function getViewportOffset() {
		return {
			top:  w.pageYOffset || documentElement.scrollTop   || d.body.scrollTop,
			left: w.pageXOffset || documentElement.scrollLeft  || d.body.scrollLeft
		};
	}

	function checkInView() {
		var $elements = $(), elementsLength, i = 0;

		$.each(inviewObjects, function(i, inviewObject) {
			var selector  = inviewObject.data.selector,
				$element  = inviewObject.$element;
			$elements = $elements.add(selector ? $element.find(selector) : $element);
		});

		elementsLength = $elements.length;
		if (elementsLength) {
			viewportSize   = viewportSize   || getViewportSize();
			viewportOffset = viewportOffset || getViewportOffset();

			for (; i<elementsLength; i++) {
				// Ignore elements that are not in the DOM tree
				if (!$.contains(documentElement, $elements[i])) {
					continue;
				}

				var $element      = $($elements[i]),
					elementSize   = { height: $element.height(), width: $element.width() },
					elementOffset = $element.offset(),
					inView        = $element.data('inview'),
					visiblePartX,
					visiblePartY,
					visiblePartsMerged;

				// Don't ask me why because I haven't figured out yet:
				// viewportOffset and viewportSize are sometimes suddenly null in Firefox 5.
				// Even though it sounds weird:
				// It seems that the execution of this function is interferred by the onresize/onscroll event
				// where viewportOffset and viewportSize are unset
				if (!viewportOffset || !viewportSize) {
					return;
				}

				if (elementOffset.top + elementSize.height > viewportOffset.top &&
					elementOffset.top < viewportOffset.top + viewportSize.height &&
					elementOffset.left + elementSize.width > viewportOffset.left &&
					elementOffset.left < viewportOffset.left + viewportSize.width) {
					visiblePartX = (viewportOffset.left > elementOffset.left ?
						'right' : (viewportOffset.left + viewportSize.width) < (elementOffset.left + elementSize.width) ?
						'left' : 'both');
					visiblePartY = (viewportOffset.top > elementOffset.top ?
						'bottom' : (viewportOffset.top + viewportSize.height) < (elementOffset.top + elementSize.height) ?
						'top' : 'both');
					visiblePartsMerged = visiblePartX + "-" + visiblePartY;
					if (!inView || inView !== visiblePartsMerged) {
						$element.data('inview', visiblePartsMerged).trigger('inview', [true, visiblePartX, visiblePartY]);
					}
				} else if (inView) {
					$element.data('inview', false).trigger('inview', [false]);
				}
			}
		}
	}

	$(w).bind("scroll resize", function() {
		viewportSize = viewportOffset = null;
	});

	// IE < 9 scrolls to focused elements without firing the "scroll" event
	if (!documentElement.addEventListener && documentElement.attachEvent) {
		documentElement.attachEvent("onfocusin", function() {
			viewportOffset = null;
		});
	}

	// Use setInterval in order to also make sure this captures elements within
	// "overflow:scroll" elements or elements that appeared in the dom tree due to
	// dom manipulation and reflow
	// old: $(window).scroll(checkInView);
	//
	// By the way, iOS (iPad, iPhone, ...) seems to not execute, or at least delays
	// intervals while the user scrolls. Therefore the inview event might fire a bit late there
	setInterval(checkInView, 250);
})(jQuery);