/**
 * 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 (factory) {
  if (typeof define == 'function' && define.amd) {
    // amd
    define(['jquery'], factory);
  } else if (typeof exports === 'object') {
    // node, commonjs
    module.exports = factory(require('jquery'));
  } else {
      // browser globals
    factory(jquery);
  }
}(function ($) {

  var inviewobjects = [], viewportsize, viewportoffset,
      d = document, w = window, documentelement = d.documentelement, timer;

  $.event.special.inview = {
    add: function(data) {
      inviewobjects.push({ data: data, $element: $(this), element: this });
      // 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
      //
      // don't waste cycles with an interval until we get at least one element that
      // has bound to the inview event.
      if (!timer && inviewobjects.length) {
         timer = setinterval(checkinview, 250);
      }
    },

    remove: function(data) {
      for (var i=0; i<inviewobjects.length; i++) {
        var inviewobject = inviewobjects[i];
        if (inviewobject.element === this && inviewobject.data.guid === data.guid) {
          inviewobjects.splice(i, 1);
          break;
        }
      }

      // clear interval when we no longer have any elements listening
      if (!inviewobjects.length) {
         clearinterval(timer);
         timer = null;
      }
    }
  };

  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() {
    if (!inviewobjects.length) {
      return;
    }

    var i = 0, $elements = $.map(inviewobjects, function(inviewobject) {
      var selector  = inviewobject.data.selector,
          $element  = inviewobject.$element;
      return selector ? $element.find(selector) : $element;
    });

    viewportsize   = viewportsize   || getviewportsize();
    viewportoffset = viewportoffset || getviewportoffset();

    for (; i<inviewobjects.length; i++) {
      // ignore elements that are not in the dom tree
      if (!$.contains(documentelement, $elements[i][0])) {
        continue;
      }

      var $element      = $($elements[i]),
          elementsize   = { height: $element[0].offsetheight, width: $element[0].offsetwidth },
          elementoffset = $element.offset(),
          inview        = $element.data('inview');

      // 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) {
        if (!inview) {
          $element.data('inview', true).trigger('inview', [true]);
        }
      } else if (inview) {
        $element.data('inview', false).trigger('inview', [false]);
      }
    }
  }

  $(w).bind("scroll resize scrollstop", 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;
    });
  }
}));