$.fn.extend({
    TrunAd: function(options) {
        var auto = null;
        var obj = this;
        var current = 0;

        var settings = { timer: 5000, menu: "#playMenu", menuType: "image" };
        options = options || {};


        //这句是什么意思？
        $.extend(settings, options);

        var $playMenu = $("<div id='playMenu'></div>");
        var ulcontent = "<ul>";
        $('a', this).each(function(i) {
            if (i == 0) {
                ulcontent = ulcontent + "<li style='margin-left:0px;'><a href='" + $(this).attr("href") + "' target='_blank'><img border='0' src='" + $("img", $(this)).attr("src").substring(0, $("img", $(this)).attr("src").lastIndexOf(".")) + "_small_1.jpg'  longDesc='" + $("img", $(this)).attr("src").substring(0, $("img", $(this)).attr("src").lastIndexOf(".")) + "_small_2.jpg'  class='smallpic'/></a></li>"
            }
            else {
                ulcontent = ulcontent + "<li><a href='" + $(this).attr("href") + "' target='_blank'><img border='0'  src='" + $("img", $(this)).attr("src").substring(0, $("img", $(this)).attr("src").lastIndexOf(".")) + "_small_1.jpg'  longDesc='" + $("img", $(this)).attr("src").substring(0, $("img", $(this)).attr("src").lastIndexOf(".")) + "_small_2.jpg'  class='smallpic'/></a></li>"
            }
        });
        ulcontent = ulcontent + "</ul>";
        $playMenu.append(ulcontent);
        $playMenu.insertAfter(this);



        $('li', $(settings.menu)).each(function(i) {
            $(this).mouseover(function() {
                current = i;
                clearInterval(auto);
                ChangeStatus(i);


            }).mouseout(function() {
                auto = AutoChangeStatus();
            });
        });


        function changeImgSrc(obj) {
            var t = obj.attr("src");
            obj.attr("src", obj.attr("longDesc"));
            obj.attr("longDesc", t);
            return obj;
        }


        function ChangeStatus(i) {
            $("a", obj).hide();
            $($("a", obj).get(i)).show();

            changeImgSrc($('.smallpic_hover', $(settings.menu))).addClass('smallpic').removeClass('smallpic_hover');
            changeImgSrc($($('img', $(settings.menu)).get(i))).addClass('smallpic_hover').removeClass('smallpic');
        }

        function AutoChangeStatus() {
            return setInterval(function() {
                current++;
                if (current >= $("li", $(settings.menu)).length) {
                    current = 0;
                }
                ChangeStatus(current);
            }, settings.timer);
        }

        $("li", $(settings.menu)).eq(0).trigger("mouseover");
        auto = AutoChangeStatus();

    }

});