(function (root) {

  function __() {

    var Animations = {

      rotateX: function (pct, fromValue, toValue) {
        var deg = fromValue + ((toValue - fromValue) * pct);
        return {
          property: 'transform',
          value: 'rotateX(' + deg + 'deg)';
        }
      },

      rotateY: function (pct, fromValue, toValue) {
        var deg = fromValue + ((toValue - fromValue) * pct);
        return {
          property: 'transform',
          value: 'rotateY(' + deg + 'deg)';
        }
      },

      scale: function (pct, fromValue, toValue) {
        var num = fromValue + ((toValue - fromValue) * pct);
        return {
          property: 'transform',
          value: 'scale(' + num + ')';
        }
      }

    };

    var StyleValuesHandler = {

      transform: function (values) {
        return values.join(' ');
      }

    };

    var Animation = function (el, action, options) {
      options = options || {};
      this.el = el;

      if ('function' === typeof action) {
        this.action = action;
      } else {
        this.action = Animations[action];
      }

      this.from = options.from || 0;
      delete options.from;

      this.fromValue = options.fromValue;
      delete options.from;

      this.to = options.to || 0;
      delete options.to;

      this.toValue = options.toValue;
      delete options.toValue;

      this.options = options;
    }

    Animation.prototype = {

      current: function (y) {
        var pct = (this.to - this.from) / y;
        return this.action(pct, this.fromValue, this.toValue, this.options);
      }

    };

    var Scroller = function () {
      this.animations = [];
    };

    Scroller.prototype = {

      animate: function (el, action, options) {
        var animation = new Animation(el, action, options);
        this.animations.push(animation);
        return this;
      },

      bind: function (win) {
        return win.onScroll = function () {
          var y = win.pageYOffset, styles = {}, animation, current, el, property, value;
          for (var i=0; i<this.animations.length; i++) {
            animation = this.animations[i];
            if (animation.from >= y && animation.to <= y) {
              el = animation.el;
              current = animation.current(y);
              property = current.property;
              value = current.value;
              if (!styles[el]) styles[el] = {};
              if (!styles[el][property]) styles[el][property] = [];
              styles[el][property].push(value);
            }
          }
          var props, $el, value;
          for (var el in styles) {
            props = styles[el];
            $el = document.querySelector(el);
            for (var key in props) {
              value = (props[key].length > 1) ? StyleValuesHandler[key](props[key]) : props[key][0];
              $el.style[key] = value;
            }
          }
        }.bind(this));
      }

    }

    return Scroller;

  };

  if ('function' === typeof define && define.amd) {
    define(__);
  } else {
    root.Scroller = __();
  };

})(this);