;(function () {
  var _ = this._ || require('underscore');
  var $ = this.jQuery || require('jquery');
  var Backbone = this.Backbone || require('backbone');
  Backbone.$ = $;
  
  function Watchcss(el, props) {
    this.el = el;
    props || (props = []);

    this.props = props;

    var propsModel = new (Backbone.Model.extend())(_.object(props, [""]));

    var propschanges = [];
    propsModel.on('change', function (model) {
      _(model.changed).each(function (val, propName) {
        propschanges.push({
          propName: propName,
          oldValue: model._previousAttributes[propName],
          newValue: val
        });
      });
    });

    this.mo = new MutationObserver(function (muts) {
      var i = muts.length;
      while (i--) {
        if (muts[i].attributeName !== 'style') continue; // only style mutation

        propschanges = []; // empty

        var mut = muts[i];
        var j = this.props.length;
        while (j--) {
          var prop = this.props[j];
          propsModel.set(prop, mut.target.style[prop]);
        }

        // 'change' event
        if (propschanges.length) {
          this.trigger('change', propschanges);

          // 'change:<prop>' event
          var l = propschanges.length;
          while (l--) {
            var propchange = propschanges[l];
            this.trigger('change:'+propchange.propName, propchange);
          }
        }
      }
    }.bind(this));

    this.observe();
  }
  _.extend(Watchcss.prototype, Backbone.Events);
  Watchcss.prototype.observe = function () {
    this.mo.observe(this.el, {attributes: true});
    return this;
  };
  Watchcss.prototype.disconnect = function () {
    this.mo.disconnect();
    return this;
  };
  window.Watchcss = Watchcss;

  $.fn.watchcss = function (props) {
    props || (props = []);

    var $el = this;

    var instance = $el.data('watchcss');
    if (instance) {
      instance.props = _.uniq(instance.props.concat(props));
    } else {
      instance = new Watchcss($el[0], props);
      $el.data('watchcss', instance);
    }

    return instance;
  }
}).call(this);