/* appear.js 1.2.1 */
(function(window){
  'use strict';
  var scrollLastPos = null, scrollTimer = 0, scroll = {};

  function track(){
    var newPos = window.scrollY || window.pageYOffset;  // pageYOffset for IE9
    if ( scrollLastPos != null ){
      scroll.velocity = newPos - scrollLastPos;
      scroll.delta = (scroll.velocity >= 0) ? scroll.velocity : (-1 * scroll.velocity);
      
    }
    scrollLastPos = newPos;
    if(scrollTimer){
      clearTimeout(scrollTimer);
    }
    scrollTimer = setTimeout(function(){
      scrollLastPos = null;
    }, 30);
  }
  addEventListener('scroll', track, false);

  // determine if a given element (plus an additional "bounds" area around it) is in the viewport
  function viewable(el, bounds){
    var rect = el.getBoundingClientRect();
    return (
      (rect.top + rect.height) >= 0 &&
      (rect.left + rect.width) >= 0 &&
      (rect.bottom - rect.height) <= ( (window.innerHeight || document.documentElement.clientHeight) + bounds) &&
      (rect.right - rect.width) <= ( (window.innerWidth || document.documentElement.clientWidth) + bounds)
    );
  }

  return function(obj){

    return (function(obj){
      var initd = false, elements = [], elementsLength, reappear = [],
        appeared = 0, disappeared = 0, timer, deltaSet, opts = {}, done;

      // handle debouncing a function for better performance on scroll
      function debounce(fn, delay) {
        return function () {
          var self = this, args = arguments;
          clearTimeout(timer);
          
          timer = setTimeout(function () {
            fn.apply(self, args);
          }, delay);
        };
      }

      // called on scroll and resize event, so debounce the actual function that does
      // the heavy work of determining if an item is viewable and then "appearing" it
      function checkAppear() {
        if(scroll.delta < opts.delta.speed) {
          if(!deltaSet) {
            deltaSet = true;
            doCheckAppear();
            setTimeout(function(){
              deltaSet = false;
            }, opts.delta.timeout);
          }
        }
        (debounce(function() {
          doCheckAppear();
        }, opts.debounce)());
      }

      function begin() {
        // initial appear check before any scroll or resize event
        doCheckAppear();

        // add relevant listeners
        addEventListener('scroll', checkAppear, false);
        addEventListener('resize', checkAppear, false);
      }

      function end() {
        elements = [];
        if(timer) {
          clearTimeout(timer);
        }
        removeListeners();
      }

      function removeListeners() {
        
        removeEventListener('scroll', checkAppear, false);
        removeEventListener('resize', checkAppear, false);
      }

      function doCheckAppear() {
        if(done) {
          return;
        }
        
        elements.forEach(function(n, i){
          if(n && viewable(n, opts.bounds)) {
            // only act if the element is eligible to reappear
            if(reappear[i]) {
              // mark this element as not eligible to appear
              reappear[i] = false;
              // increment the count of appeared items
              appeared++;
              
              // call the appear fn
              if(opts.appear) {
                opts.appear(n);
              }
              // if not tracking reappears or disappears, need to remove node here
              if(!opts.disappear && !opts.reappear) {
                // stop tracking this node, which is now viewable
                elements[i] = null;
              }
            }
          } else {
            if(reappear[i] === false) {
              if(opts.disappear) {
                opts.disappear(n);
              }
              // increment the dissappeared count
              disappeared++;
              
              // if not tracking reappears, need to remove node here
              if(!opts.reappear) {
                // stop tracking this node, which is now viewable
                elements[i] = null;
              }
            }
            // element is out of view and eligible to be appeared again
            reappear[i] = true;
          }
        });

        // remove listeners if all items have (re)appeared
        if(!opts.reappear && (!opts.appear || opts.appear && appeared === elementsLength) && (!opts.disappear || opts.disappear && disappeared === elementsLength)) {
          // ensure done is only called once (could be called from a trailing debounce/throttle)
          done = true;
          removeListeners();
          // all items have appeared, so call the done fn
          if(opts.done){
            opts.done();
          }
        }
      }

      function init() {
        // make sure we only init once
        if(initd) {
          return;
        }
        initd = true;

        // call the obj init fn
        if(opts.init) {
          opts.init();
        }
        // get the elements to work with
        var els;
        if(typeof opts.elements === 'function') {
          els = opts.elements();
        } else {
          els = opts.elements;
        }
        if(els) {
          //  put elements into an array object to work with
          elementsLength = els.length;
          for(var i = 0; i < elementsLength; i += 1) {
            elements.push(els[i]);
            reappear.push(true);
          }
          begin();
        }
      }

      var appear = function(obj) {
        obj = obj || {};

        // assign the fn to execute when a node is visible
        opts = {
          // a function to be run when the dom is ready (allows for any setup work)
          init: obj.init,
          // either an array of elements or a function that will return an htmlCollection
          elements: obj.elements,
          // function to call when an element is "viewable", will be passed the element to work with
          appear: obj.appear,
          // function to call when an element is no longer "viewable", will be passed the element to work with
          disappear: obj.disappear,
          // function to call when all the elements have "appeared"
          done: obj.done,
          // keep tracking the elements
          reappear: obj.reappear,
          // the extra border around an element to make it viewable outside of the true viewport
          bounds: obj.bounds || 0,
          // the debounce timeout
          debounce: obj.debounce || 50,
          // appear.js will also check for items on continuous slow scrolling
          // you can controll how slow the scrolling should be  (deltaSpeed)
          // and when it will check again (deltaTimeout) after it has inspected the dom/viewport;
          delta: {
            speed: obj.deltaSpeed || 50,
            timeout: obj.deltaTimeout || 500
          }
        };

        // add an event listener to init when dom is ready
        addEventListener('DOMContentLoaded', init, false);

        // http://stackoverflow.com/questions/9900311/how-do-i-target-only-internet-explorer-10-for-certain-situations-like-internet-e/13971998#13971998
        var isIE10 = false;
        if (Function('/*@cc_on return document.documentMode===10@*/')()){
          isIE10 = true;
        }
        var completeOrLoaded = document.readyState === 'complete' || document.readyState === 'loaded';

        // call init if document is ready to be worked with and we missed the event
        if (isIE10) {
          if (completeOrLoaded) {
            init();
          }
        } else {
          if (completeOrLoaded || document.readyState === 'interactive') {
            init();
          }
        }

        return {
          // manually fire check for visibility of tracked elements
          trigger: function trigger(){
            doCheckAppear();
          },
          // pause tracking of elements
          pause: function pause(){
            removeListeners();
          },
          // resume tracking of elements after a pause
          resume: function resume(){
            begin();
          },
          // provide a means to stop monitoring all elements
          destroy: function destroy() {
            end();
          }
        };

      };

      if (typeof module !== 'undefined' && typeof module.exports !== 'undefined') {
        module.exports = appear;
      } else {
        window.appear = appear;
      }
    }()(obj));
  };
}(this));