+function ($) {
  'use strict';

  // AFFIX CLASS DEFINITION
  // ======================

  var Affix = function (element, options) {
    this.options = $.extend({}, Affix.DEFAULTS, options);

    this.$target = $(this.options.target)
      .on('scroll.bs.affix.data-api', $.proxy(this.checkPosition, this))
      .on('click.bs.affix.data-api', $.proxy(this.checkPositionWithEventLoop, this));

    this.$element = $(element);
    this.affixed = null;
    this.unpin = null;
    this.pinnedOffset = null;

    this.checkPosition();
  };

  Affix.VERSION = '1.0.0';
  Affix.RESET = 'affix affix-top affix-bottom';
  Affix.DEFAULTS = {
    offset: 0,
    target: window
  };

  Affix.prototype.constructor = Affix;

  Affix.prototype.getState = function (scrollHeight, height, offsetTop, offsetBottom) {
    var scrollTop = this.$target.scrollTop();
    var position = this.$element.offset();
    var targetHeight = this.$target.height();

    if (offsetTop !== null && this.affixed === 'top') {
      return scrollTop < offsetTop ? 'top' : false;
    }

    if (this.affixed === 'bottom') {
      if (offsetTop !== null) {
        return (scrollTop + this.unpin <= position.top) ? false : 'bottom';
      }

      return (scrollTop + targetHeight <= scrollHeight - offsetBottom) ? false : 'bottom';
    }

    var initializing = this.affixed === null;
    var colliderTop = initializing ? scrollTop : position.top;
    var colliderHeight = initializing ? targetHeight : height;

    if (offsetTop !== null && scrollTop <= offsetTop) return 'top';
    if (offsetBottom !== null && (colliderTop + colliderHeight >= scrollHeight - offsetBottom)) return 'bottom';

    return false;
  };

  Affix.prototype.getPinnedOffset = function () {
    if (this.pinnedOffset) return this.pinnedOffset;

    this.$element
      .removeClass(Affix.RESET)
      .addClass('affix');

    var scrollTop = this.$target.scrollTop();
    var position = this.$element.offset();

    return (this.pinnedOffset = position.top - scrollTop);
  };

  Affix.prototype.checkPositionWithEventLoop = function () {
    setTimeout($.proxy(this.checkPosition, this), 1);
  };

  Affix.prototype.checkPosition = function () {
    if (!this.$element.is(':visible')) return;

    var height = this.$element.height();
    var offset = this.options.offset;
    var offsetTop = offset.top;
    var offsetBottom = offset.bottom;
    var scrollHeight = Math.max($(document).height(), $(document.body).height());

    if (typeof offset != 'object') {
      offsetBottom = offsetTop = offset;
    }
    if (typeof offsetTop === 'function') {
      offsetTop = offset.top(this.$element);
    }
    if (typeof offsetBottom === 'function') {
      offsetBottom = offset.bottom(this.$element);
    }

    var affix = this.getState(scrollHeight, height, offsetTop, offsetBottom);

    if (this.affixed != affix) {
      if (this.unpin !== null) this.$element.css('top', '');

      var affixType = 'affix' + (affix ? '-' + affix : '');
      var e = $.Event(affixType + '.bs.affix');

      this.$element.trigger(e);

      if (e.isDefaultPrevented()) return;

      this.affixed = affix;
      this.unpin = affix === 'bottom' ? this.getPinnedOffset() : null;

      this.$element
        .removeClass(Affix.RESET)
        .addClass(affixType)
        .trigger(affixType.replace('affix', 'affixed') + '.bs.affix');
    }

    if (affix === 'bottom') {
      this.$element.offset({
        top: scrollHeight - height - offsetBottom
      });
    }
  };

  // AFFIX PLUGIN DEFINITION
  // =======================

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

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

  var old = $.fn.affix;

  $.fn.affix = Plugin;
  $.fn.affix.Constructor = Affix;

  // AFFIX NO CONFLICT
  // =================

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

  // AFFIX DATA-API
  // ==============

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

      data.offset = data.offset || {};

      if (data.offsetBottom !== null) {
        data.offset.bottom = data.offsetBottom;
      }
      if (data.offsetTop !== null) {
        data.offset.top = data.offsetTop;
      }

      Plugin.call($this, data);
    });
  });

}(jQuery);