// JavaScript Document
var $ = function(id) {   
    return "string" == typeof id ? document.getElementById(id) : id;   
};   
// 实例化一个对象并调用对象的initialize方法   
var Class = {   
    create : function() {   
        return function() {   
            this.initialize.apply(this, arguments);   
        };   
    }   
};   
// 为Object添加一个extend方法   
Object.extend = function(destination, source) {   
    for ( var property in source) {   
        destination[property] = source[property];   
    }   
    return destination;   
};   
// 为对象注册事件   
var addEventHandler = function(oTarget, sEventType, fnHandler) {   
    if (oTarget.addEventListener) {   
        oTarget.addEventListener(sEventType, fnHandler, false);   
    } else if (oTarget.attachEvent) {   
        oTarget.attachEvent("on" + sEventType, fnHandler);   
    } else {   
        oTarget["on" + sEventType] = fnHandler;   
    }   
};   
var Scroll = Class.create();   
Scroll.prototype = {   
    initialize : function(outObj, inObj, options) {   
        var oScroll = this;   
        var iOut = $(outObj);   
        var iIn = $(inObj);   
        this.outHeight = iOut.offsetHeight;   
        this.inHeight = iIn.offsetHeight;   
  
        if (this.outHeight >= this.inHeight) return;   
  
        iOut.style.overflow = "hidden";   
        iIn.appendChild(iIn.cloneNode(true));   
  
        this.setOptions(options);   
        this.outObj = iOut;   
        this.timer = null;   
  
        this.side = 1; // 1：向上；2：向下   
        switch(this.options.side) {   
            case "down" :   
                this.side = -1;   
                break;   
            case "up":   
            default:   
                this.side = 1;   
        }   
        addEventHandler(iIn, "mouseover", function() {oScroll.stop();});   
        addEventHandler(iIn, "mouseout", function() {oScroll.start();});   
        this.start();   
    },   
    setOptions : function(options) {   
        this.options = {   
            step : 1, // 每次滚动的px量   
            side : "up", // 滚动的方向   
            time : 10 // 滚动的间隔时间（滚动速度）   
        };   
        Object.extend(this.options, options || {});   
    },   
    scroll : function() {   
        var inHeight = this.inHeight, outHeight = this.outHeight, iStep = this.options.step * this.side, time = this.options.time;   
        var iScrollTop = this.outObj.scrollTop;   
        if (iScrollTop >= (inHeight * 2 - outHeight)) {   
            iScrollTop -= inHeight;   
        } else if (iScrollTop <= 0) {   
            iScrollTop += inHeight;   
        }          
        this.outObj.scrollTop = iScrollTop + iStep;   
           
        var oScroll = this;   
        this.timer = setTimeout(function() {oScroll.scroll();}, time);   
    },    
    start : function() {   
        this.scroll();   
    },   
    stop : function() {   
        clearTimeout(this.timer);   
    }   
};