/**
 * @ngdoc function
 * @name angular.module.ng.$autoScroll
 * @requires $window
 * @requires $location
 * @requires $rootScope
 *
 * @description
 * When called, it checks current value of `$location.hash()` and scroll to related element,
 * according to rules specified in
 * {@link http://dev.w3.org/html5/spec/Overview.html#the-indicated-part-of-the-document Html5 spec}.
 *
 * If `$location` uses `hashbang` url (running in `hashbang` mode or `html5` mode on browser without
 * history API support), `$autoScroll` watches the `$location.hash()` and scroll whenever it
 * changes.
 *
 * You can disable `$autoScroll` service by calling `disable()` on `$autoScrollProvider`.
 * Note: disabling is only possible before the service is instantiated !
 */
function $AutoScrollProvider() {

  this.disable = function() {
    this.$get = function() {return noop;};
  };

  this.$get = ['$window', '$location', '$rootScope', function($window, $location, $rootScope) {
    var document = $window.document;

    // helper function to get first anchor from a NodeList
    // can't use filter.filter, as it accepts only instances of Array
    // and IE can't convert NodeList to an array using [].slice
    // TODO(vojta): use filter if we change it to accept lists as well
    function getFirstAnchor(list) {
      var result = null;
      forEach(list, function(element) {
        if (!result && lowercase(element.nodeName) === 'a') result = element;
      });
      return result;
    }

    function scroll() {
      var hash = $location.hash(), elm;

      // empty hash, scroll to the top of the page
      if (!hash) $window.scrollTo(0, 0);

      // element with given id
      else if ((elm = document.getElementById(hash))) elm.scrollIntoView();

      // first anchor with given name :-D
      else if ((elm = getFirstAnchor(document.getElementsByName(hash)))) elm.scrollIntoView();

      // no element and hash == 'top', scroll to the top of the page
      else if (hash === 'top') $window.scrollTo(0, 0);
    }

    // scroll whenever hash changes (with hashbang url, regular urls are handled by browser)
    if ($location instanceof LocationHashbangUrl) {
      $rootScope.$watch(function() {return $location.hash();}, function() {
        $rootScope.$evalAsync(scroll);
      });
    }

    return scroll;
  }];
}