(function() {
'use strict';

/*
 * @ngdoc module
 * @name material.components.sticky
 * @description
 *
 * Sticky effects for md
 */

angular.module('material.components.sticky', [
  'material.core',
  'material.components.content'
])
  .factory('$mdSticky', MdSticky);

/*
 * @ngdoc service
 * @name $mdSticky
 * @module material.components.sticky
 *
 * @description
 * The `$mdSticky`service provides a mixin to make elements sticky.
 *
 * @returns A `$mdSticky` function that takes three arguments:
 *   - `scope`
 *   - `element`: The element that will be 'sticky'
 *   - `elementClone`: A clone of the element, that will be shown
 *     when the user starts scrolling past the original element.
 *     If not provided, it will use the result of `element.clone()`.
 */

function MdSticky($document, $mdConstant, $compile, $$rAF, $mdUtil) {

  var browserStickySupport = checkStickySupport();

  /**
   * Registers an element as sticky, used internally by directives to register themselves
   */
  return function registerStickyElement(scope, element, stickyClone) {
    var contentCtrl = element.controller('mdContent');
    if (!contentCtrl) return;

    if (browserStickySupport) {
      element.css({
        position: browserStickySupport,
        top: 0,
        'z-index': 2
      });
    } else {
      var $$sticky = contentCtrl.$element.data('$$sticky');
      if (!$$sticky) {
        $$sticky = setupSticky(contentCtrl);
        contentCtrl.$element.data('$$sticky', $$sticky);
      }

      var deregister = $$sticky.add(element, stickyClone || element.clone());
      scope.$on('$destroy', deregister);
    }
  };

  function setupSticky(contentCtrl) {
    var contentEl = contentCtrl.$element;

    // Refresh elements is very expensive, so we use the debounced
    // version when possible.
    var debouncedRefreshElements = $$rAF.debounce(refreshElements);

    // setupAugmentedScrollEvents gives us `$scrollstart` and `$scroll`,
    // more reliable than `scroll` on android.
    setupAugmentedScrollEvents(contentEl);
    contentEl.on('$scrollstart', debouncedRefreshElements);
    contentEl.on('$scroll', onScroll);

    var self;
    return self = {
      prev: null,
      current: null, //the currently stickied item
      next: null,
      items: [],
      add: add,
      refreshElements: refreshElements
    };

    /***************
     * Public
     ***************/
    // Add an element and its sticky clone to this content's sticky collection
    function add(element, stickyClone) {
      stickyClone.addClass('md-sticky-clone');

      var item = {
        element: element,
        clone: stickyClone
      };
      self.items.push(item);

      contentEl.parent().prepend(item.clone);

      debouncedRefreshElements();

      return function remove() {
        self.items.forEach(function(item, index) {
          if (item.element[0] === element[0]) {
            self.items.splice(index, 1);
            item.clone.remove();
          }
        });
        debouncedRefreshElements();
      };
    }

    function refreshElements() {
      // Sort our collection of elements by their current position in the DOM.
      // We need to do this because our elements' order of being added may not
      // be the same as their order of display.
      self.items.forEach(refreshPosition);
      self.items = self.items.sort(function(a, b) {
        return a.top < b.top ? -1 : 1;
      });

      // Find which item in the list should be active, 
      // based upon the content's current scroll position
      var item;
      var currentScrollTop = contentEl.prop('scrollTop');
      for (var i = self.items.length - 1; i >= 0; i--) {
        if (currentScrollTop > self.items[i].top) {
          item = self.items[i];
          break;
        }
      }
      setCurrentItem(item);
    }


    /***************
     * Private
     ***************/

    // Find the `top` of an item relative to the content element,
    // and also the height.
    function refreshPosition(item) {
      // Find the top of an item by adding to the offsetHeight until we reach the 
      // content element.
      var current = item.element[0];
      item.top = 0;
      item.left = 0;
      while (current && current !== contentEl[0]) {
        item.top += current.offsetTop;
        item.left += current.offsetLeft;
        current = current.offsetParent;
      }
      item.height = item.element.prop('offsetHeight');
      item.clone.css('margin-left', item.left + 'px');
    }


    // As we scroll, push in and select the correct sticky element.
    function onScroll() {
      var scrollTop = contentEl.prop('scrollTop');
      var isScrollingDown = scrollTop > (onScroll.prevScrollTop || 0);
      onScroll.prevScrollTop = scrollTop;

      // At the top?
      if (scrollTop === 0) {
        setCurrentItem(null);

      // Going to next item?
      } else if (isScrollingDown && self.next) {
        if (self.next.top - scrollTop <= 0) {
          // Sticky the next item if we've scrolled past its position.
          setCurrentItem(self.next);
        } else if (self.current) {
          // Push the current item up when we're almost at the next item.
          if (self.next.top - scrollTop <= self.next.height) {
            translate(self.current, self.next.top - self.next.height - scrollTop);
          } else {
            translate(self.current, null);
          }
        }
        
      // Scrolling up with a current sticky item?
      } else if (!isScrollingDown && self.current) {
        if (scrollTop < self.current.top) {
          // Sticky the previous item if we've scrolled up past
          // the original position of the currently stickied item.
          setCurrentItem(self.prev);
        }
        // Scrolling up, and just bumping into the item above (just set to current)?
        // If we have a next item bumping into the current item, translate
        // the current item up from the top as it scrolls into view.
        if (self.current && self.next) {
          if (scrollTop >= self.next.top - self.current.height) {
            translate(self.current, self.next.top - scrollTop - self.current.height);
          } else {
            translate(self.current, null);
          }
        }
      }
    }
     
   function setCurrentItem(item) {
     if (self.current === item) return;
     // Deactivate currently active item
     if (self.current) {
       translate(self.current, null);
       setStickyState(self.current, null);
     }

     // Activate new item if given
     if (item) {
       setStickyState(item, 'active');
     }

     self.current = item;
     var index = self.items.indexOf(item);
     // If index === -1, index + 1 = 0. It works out.
     self.next = self.items[index + 1];
     self.prev = self.items[index - 1];
     setStickyState(self.next, 'next');
     setStickyState(self.prev, 'prev');
   }

   function setStickyState(item, state) {
     if (!item || item.state === state) return;
     if (item.state) {
       item.clone.attr('sticky-prev-state', item.state);
       item.element.attr('sticky-prev-state', item.state);
     }
     item.clone.attr('sticky-state', state);
     item.element.attr('sticky-state', state);
     item.state = state;
   }

   function translate(item, amount) {
     if (!item) return;
     if (amount === null || amount === undefined) {
       if (item.translateY) {
         item.translateY = null;
         item.clone.css($mdConstant.CSS.TRANSFORM, '');
       }
     } else {
       item.translateY = amount;
       item.clone.css(
         $mdConstant.CSS.TRANSFORM, 
         'translate3d(' + item.left + 'px,' + amount + 'px,0)'
       );
     }
   }
  }

  // Function to check for browser sticky support
  function checkStickySupport($el) {
    var stickyProp;
    var testEl = angular.element('<div>');
    $document[0].body.appendChild(testEl[0]);

    var stickyProps = ['sticky', '-webkit-sticky'];
    for (var i = 0; i < stickyProps.length; ++i) {
      testEl.css({position: stickyProps[i], top: 0, 'z-index': 2});
      if (testEl.css('position') == stickyProps[i]) {
        stickyProp = stickyProps[i];
        break;
      }
    }
    testEl.remove();
    return stickyProp;
  }

  // Android 4.4 don't accurately give scroll events.
  // To fix this problem, we setup a fake scroll event. We say:
  // > If a scroll or touchmove event has happened in the last DELAY milliseconds, 
  //   then send a `$scroll` event every animationFrame.
  // Additionally, we add $scrollstart and $scrollend events.
  function setupAugmentedScrollEvents(element) {
    var SCROLL_END_DELAY = 200;
    var isScrolling;
    var lastScrollTime;
    element.on('scroll touchmove', function() {
      if (!isScrolling) {
        isScrolling = true;
        $$rAF(loopScrollEvent);
        element.triggerHandler('$scrollstart');
      }
      element.triggerHandler('$scroll');
      lastScrollTime = +$mdUtil.now();
    });

    function loopScrollEvent() {
      if (+$mdUtil.now() - lastScrollTime > SCROLL_END_DELAY) {
        isScrolling = false;
        element.triggerHandler('$scrollend');
      } else {
        element.triggerHandler('$scroll');
        $$rAF(loopScrollEvent);
      }
    }
  }

}
})();
