+function ($) {
  'use strict';

  // SCROLLSPY CLASS DEFINITION
  // ==========================

  function ScrollSpy(element, options) {
    this.$body = $(document.body);
    this.$scrollElement = $(element).is(document.body) ? $(window) : $(element);
    this.options = $.extend({}, ScrollSpy.DEFAULTS, options);

    this.selector = (this.options.target || '') + ' .scrollspy li > a';
    this.offsets = [];
    this.targets = [];
    this.activeTarget = null;
    this.scrollHeight = 0;
    this.$scrollElement.on('scroll.bs.scrollspy', $.proxy(this.process, this));

    this.refresh();
    this.process();
  }

  ScrollSpy.VERSION  = '1.0.0';
  ScrollSpy.DEFAULTS = {
    offset: 10
  };

  ScrollSpy.prototype.constructor = ScrollSpy;

  ScrollSpy.prototype.getScrollHeight = function () {
    return this.$scrollElement[0].scrollHeight ||
      Math.max(this.$body[0].scrollHeight, document.documentElement.scrollHeight);
  };

  ScrollSpy.prototype.refresh = function () {
    var that = this;
    var offsetMethod = 'offset';
    var offsetBase = 0;

    this.offsets = [];
    this.targets = [];
    this.scrollHeight = this.getScrollHeight();

    if (!$.isWindow(this.$scrollElement[0])) {
      offsetMethod = 'position';
      offsetBase = this.$scrollElement.scrollTop();
    }

    this.$body
      .find(this.selector)
      .map(function () {
        var $el = $(this);
        var href = $el.data('target') || $el.attr('href');
        var $href = /^#./.test(href) && $(href);

        return ($href &&
          $href.length &&
          $href.is(':visible') &&
          [[$href[offsetMethod]().top + offsetBase, href]]) ||
          null;
      })
      .sort(function (a, b) { return a[0] - b[0]; })
      .each(function () {
        that.offsets.push(this[0]);
        that.targets.push(this[1]);
      });
  };

  ScrollSpy.prototype.process = function () {
    var scrollTop = this.$scrollElement.scrollTop() + this.options.offset;
    var scrollHeight = this.getScrollHeight();
    var maxScroll = this.options.offset + scrollHeight - this.$scrollElement.height();
    var offsets = this.offsets;
    var targets = this.targets;
    var activeTarget = this.activeTarget;
    var i;

    if (this.scrollHeight !== scrollHeight) this.refresh();

    if (scrollTop >= maxScroll) {
      return activeTarget !== (i = targets[targets.length - 1]) && this.activate(i);
    }

    if (activeTarget && scrollTop < offsets[0]) {
      this.activeTarget = null;
      return this.clear();
    }

    for (i = offsets.length; i--;) {
      activeTarget !== targets[i] &&
        scrollTop >= offsets[i] &&
        (offsets[i + 1] === undefined || scrollTop < offsets[i + 1]) &&
        this.activate(targets[i])
    }
  };

  ScrollSpy.prototype.activate = function (target) {
    this.activeTarget = target;
    this.clear();

    var selector = this.selector +
      '[data-target="' + target + '"],' +
      this.selector + '[href="' + target + '"]';

    var active = $(selector)
      .parents('li')
      .addClass('active');

    if (active.parent('.dropmenu').length) {
      active = active
        .closest('li.dropdown')
        .addClass('active');
    }

    active.trigger('activate.bs.scrollspy');
  };

  ScrollSpy.prototype.clear = function () {
    $(this.selector)
      .parentsUntil(this.options.target, '.active')
      .removeClass('active');
  };

  // SCROLLSPY PLUGIN DEFINITION
  // ===========================

  function Plugin(option) {
    return this.each(function () {
      var $this = $(this);
      var data = $this.data('bs.scrollspy');
      var options = typeof option === 'object' && option;

      if (!data) $this.data('bs.scrollspy', (data = new ScrollSpy(this, options)));
      if (typeof option === 'string') data[option]();
    });
  }

  var old = $.fn.scrollspy;

  $.fn.scrollspy = Plugin;
  $.fn.scrollspy.Constructor = ScrollSpy;

  // SCROLLSPY NO CONFLICT
  // =====================

  $.fn.scrollspy.noConflict = function () {
    $.fn.scrollspy = old;
    return this;
  };

  // SCROLLSPY DATA-API
  // ==================

  $(document).on('ready.bs.scrollspy.data-api', function () {
    $('[data-spy="scroll"]').each(function () {
      var $this = $(this);
      Plugin.call($this, $this.data());
    });
  });

}(jQuery);