(function($){

  $.fn.twentytwenty = function(options) {
    var options = $.extend({default_offset_pct: 0.5}, options);
    return this.each(function() {

      var sliderPct = options.default_offset_pct;
      var container = $(this);
      
      container.wrap("<div class='twentytwenty-wrapper'></div>");
      container.append("<div class='twentytwenty-overlay'></div>");
      var beforeImg = container.find("img:first");
      var afterImg = container.find("img:last");
      container.append("<div class='twentytwenty-handle'></div>");
      var slider = container.find(".twentytwenty-handle");
      slider.append("<span class='twentytwenty-left-arrow'></span>");
      slider.append("<span class='twentytwenty-right-arrow'></span>");
      container.addClass("twentytwenty-container");
      beforeImg.addClass("twentytwenty-before");
      afterImg.addClass("twentytwenty-after");
      
      var overlay = container.find(".twentytwenty-overlay");
      overlay.append("<div class='twentytwenty-before-label'></div>");
      overlay.append("<div class='twentytwenty-after-label'></div>");

      var calcOffset = function(widthPct) {
        var w = beforeImg.width();
        var h = beforeImg.height();
        return {
          w: w+"px",
          h: h+"px",
          cw: (widthPct*w)+"px"
        };
      };

      var adjustContainer = function(offset) {
        beforeImg.css("clip", "rect(0,"+offset.cw+","+offset.h+",0)");
        container.css("height", offset.h);
      };

      var adjustSlider = function(pct) {
        var offset = calcOffset(pct);
        //slider.css("height", offset.h);
        slider.css("left", offset.cw);
        adjustContainer(offset);
      }

      $(window).on("resize.twentytwenty", function(e) {
        adjustSlider(sliderPct);
      });

      var offsetX = 0;
      var imgWidth = 0;
      
      container.on("movestart", function(e) {
        if ((e.distX > e.distY && e.distX < -e.distY) || (e.distX < e.distY && e.distX > -e.distY)) {
          e.preventDefault();
        }
        container.addClass("active");
        offsetX = container.offset().left;
        imgWidth = beforeImg.width();          
      });

      container.on("moveend", function(e) {
        container.removeClass("active");
      });

      container.on("move", function(e) {
        if (container.hasClass("active")) {
          sliderPct = (e.pageX-offsetX)/imgWidth;
          if (sliderPct < 0 || sliderPct > 1) {
            e.preventDefault();
            return false;
          }
          adjustSlider(sliderPct);
        }
      });

      container.find("img").on("mousedown", function(e) {
        event.preventDefault();
      });

      $(window).trigger("resize.twentytwenty");
    });
  };

})(jQuery);