/*!
 * "position: sticky" polyfill
 * https://github.com/matthewp/position--sticky-
 * License: MIT
 */
(function () {
    var prefixTestList = ['', '-webkit-', '-ms-', '-moz-', '-o-'];
    var stickyTestElement = document.createElement('div');
    var lastKnownScrollTop = 0;
    var waitingForUpdate = false;
    // requestAnimationFrame may be prefixed
    var requestAnimationFrame = window.requestAnimationFrame ||
                                window.webkitRequestAnimationFrame ||
                                window.mozRequestAnimationFrame;
  
    for (var i = 0, l = prefixTestList.length; i < l; i++) {
        stickyTestElement.style.position = prefixTestList[i] + 'sticky';
    }
  
    var slice = Array.prototype.slice;
    function getBodyOffset(body) {
      return {
        top: body.offsetTop,
        left: body.offsetLeft
      };
    }
    function getOffset(elem) {
      var docElem,
          body,
          win,
          clientTop,
          clientLeft,
          scrollTop,
          scrollLeft,
          box = {
          top: 0,
          left: 0
        },
        doc = elem && elem.ownerDocument;
  
      if(!doc) {
        return;
      }
      if((body = doc.body) === elem) {
        return getBodyOffset(elem);
      }
      docElem = doc.documentElement;
      if(typeof elem.getBoundingClientRect !== "undefined") {
        box = elem.getBoundingClientRect();
      }
      win = window;
      clientTop = docElem.clientTop || body.clientTop || 0;
      clientLeft = docElem.clientLeft || body.clientLeft || 0;
      scrollTop = win.pageYOffset || docElem.scrollTop;
      scrollLeft = win.pageXOffset || docElem.scrollLeft;
      return {
        top: box.top + scrollTop - clientTop,
        left: box.left + scrollLeft - clientLeft
      };
    }
    function setStyle(elem, repl) {
      var style = elem.getAttribute('style').split(';'),
          newStyle = [];
  
      for(var i = 0, l = style.length; i < l; i++) {
        var both = style[i].split(':'),
            key = both[0],
            value = both[1];
  
        if(key in repl) {
          newStyle.push(key + ':' + repl[key]);
        } else {
          newStyle.push(both.join(':'));
        }
      }
      elem.setAttribute('style', newStyle.join(';'));
    }
    var cssPattern = /\s*([^{}]+?)\s*{([^{}]+?)}+/g,
        matchPosition = /\.*?position:.*?sticky.*?;/i,
        getTop = /\.*?top:(.*?);/i,
        toObserve = [];
  
    function parse(css) {
      var matches;
      css = css.replace(/(\/\*([\s\S]*?)\*\/)|(\/\/(.*)$)/gm, '').replace(/\n|\r/g, '');
  
      while((matches = cssPattern.exec(css)) !== null) {
        var selector = matches[1];
        if(matchPosition.test(matches[2]) && selector !== "#modernizr") {
          var topMatch = getTop.exec(matches[2]),
              topCSS = ((topMatch !== null) ? parseInt(topMatch[1]) : 0);
  
          var elems = slice.call(document.querySelectorAll(selector));
          matches[2] = (matches[2].trim().slice(-1) === ";") ? matches[2] : matches[2].trim() + ';';
          elems.forEach(function (elem) {
            var height = elem.offsetHeight,
                parent = elem.parentElement,
                parOff = getOffset(parent),
                parOffTop = ((parOff !== null && parOff.top !== null) ? parOff.top : 0),
                elmOff = getOffset(elem),
                elmOffTop = ((elmOff !== null && elmOff.top !== null) ? elmOff.top : 0),
                start = elmOffTop - topCSS,
                end = (parOffTop + parent.offsetHeight) - height - topCSS,
                newCSS = matches[2] + "position:fixed;width:auto;height:" + height + "px",
                dummy = document.createElement('div');
  
            dummy.innerHTML = '<span style="position:static;display:block;height:' + height + 'px;"></span>';
            toObserve.push({
              element: elem,
              parent: parent,
              repl: dummy.firstElementChild,
              start: start,
              end: end,
              oldCSS: matches[2],
              newCSS: newCSS,
              fixed: false
            });
          });
        }
      }
    }
    function setPositions() {
      var scrollTop = lastKnownScrollTop;
      waitingForUpdate = false;
      for(var i = 0, l = toObserve.length; i < l; i++) {
        var obj = toObserve[i];
        if(obj.fixed === false && scrollTop > obj.start && scrollTop < obj.end) {
          obj.element.setAttribute('style', obj.newCSS);
          obj.fixed = true;
          obj.element.classList.add('stuck');
        } else {
          if(obj.fixed === true) {
            if(scrollTop < obj.start) {
              obj.element.setAttribute('style', obj.oldCSS);
              obj.fixed = false;
              obj.element.classList.remove('stuck');
            } else {
              if(scrollTop > obj.end) {
                var absolute = getOffset(obj.element);
                absolute.position = "absolute";
                obj.element.setAttribute('style', obj.newCSS);
                setStyle(obj.element, absolute);
                obj.fixed = false;
                obj.element.classList.remove('stuck');
              }
            }
          }
        }
      }
    }
  
    // Debounced scroll handling
    function updateScrollPos() {
      lastKnownScrollTop = document.documentElement.scrollTop || document.body.scrollTop;
  
      // Only trigger a layout change if we’re not already waiting for one
      if (!waitingForUpdate) {
        waitingForUpdate = true;
        // Don’t update until next animation frame if we can, otherwise use a
        // timeout - either will help avoid too many repaints
        if (requestAnimationFrame) {
          requestAnimationFrame(setPositions);
        }
        else {
          setTimeout(setPositions, 15);
        }
      }
    }
    if (stickyTestElement.style.position.length === 0)  { window.addEventListener('scroll', updateScrollPos); }
  
    window.addEventListener('load', function () {
      var styles = slice.call(document.querySelectorAll('style'));
      styles.forEach(function (style) {
        var text = style.textContent || style.innerText;
        parse(text);
      });
      var links = slice.call(document.querySelectorAll('link'));
      links.forEach(function (link) {
        if(link.getAttribute('rel') !== 'stylesheet') {
          return;
        }
        var href = link.getAttribute('href'),
            req = new XMLHttpRequest();
        req.open('GET', href, true);
        req.onload = function (e) {
          parse(req.responseText);
  
          // Update once stylesheet loaded, in case page loaded with a scroll offset
          updateScrollPos();
        };
        req.send();
      });
    }, false);
  })();