/* 
 * wrapScroll
 * Copyright 2007 youmos <youmos.com@gmail.com>
 * http://youmos.com/project/wrapscroll
 * 
 * The wrapScroll is licensed under a 
 * Creative Commons Attribution-NonCommercial-NoDerivs License.
 *
 * http://creativecommons.org/licenses/by-nc-nd/3.0/
 *
 * It is provided "as is" and without warranty of any kind. If you wish to continue to use it,
 * free for personal or non-commercial use, $30 for commercial use,
 * or transform and build your script upon this work to distribute.
 * The permission is valid for all future versions of wrapScroll.
*/

/*--- wrapscroll.js ---*/
var wrapScroll=function(){
	this.initialize.apply(this,arguments);
};

wrapScroll.prototype={
	Version:'0.9.5',
	Monitor:0,
	Interval:500,
	Duration:60,
	marginTop:0,
	marginBottom:0,
	_timer:0,
	_obj:null,

	initialize:function(e,p,r){
		this.attach(window,'load',this.bind(this.prepare,arguments));
	},

	prepare:function(e,p,r){
		if(o=document.getElementById(e)){
			this._obj={
				'e':o,'p':(p)?document.getElementById(p):o.parentNode,'r':(r)?document.getElementById(r):null
			};
			o.style.position='absolute';
			if((c=o.offsetTop)!=(v=((o.style.top=o.offsetTop+'px')!='')?o.offsetTop:0)){
				o.style.marginTop=0;o.style.top=c+(v-c)+'px';
			}
			this.callback();
		}
	},

	callback:function(){
		f=this.event.update(this,this._obj);
		setTimeout(this.bind(this.callback),(f)?10:this.Interval);
	},

	bind:function(method,arg){
		var _this=this;var _arg=(arg)?arg:[];
		return function(){
			method.apply(_this,_arg);
		}
	},

	attach:function(e,name,func,cap){
		if(e.addEventListener){
			e.addEventListener(name,func,cap);
		}else if(e.attachEvent){
			e.attachEvent('on'+name,func);
		}
	},

	setTween:function(f,d){
		if(f){
			this.tween=f;
		}
		if(d)
			{this.Duration=d;
		}
	},

	tween:function(t,b,c,d){
		return c*(t/=d)*t+b;
	}
};

wrapScroll.prototype.event={
	prevY:0,
	monitor:0,
	nowObj:0,
	IsG:this.IsGecko,
	update:function(t,o){
		var tpos=Math.max(this.scroll(),(o.r)?this.offset(o.r)+this.height(o.r):this.offset(o.p));
		var bpos=(this.offset(o.p)+this.height(o.p))-(this.height(o.e)+t.marginBottom);
		var s=this.offset(o.e);var e=Math.min(bpos,tpos+t.marginTop);
		if((t._prev!=e)||(t._timer>t.Duration)){
			t._timer=0;
		}
		if((t._prev=e)!=s){
			o.e.style.top=t.tween(t._timer++,s,e-s,t.Duration,o.e.style)+'px';return true;
		}
		return false;
	},
	scroll:function(){
		return document.body.scrollTop||document.documentElement.scrollTop;
	},

	height:function(o){
		return o.offsetHeight||document.body.scrollHeight||document.documentElement.scrollHeight;
	},

	offset:function(o){
		y=o.offsetTop;
		if(o.id=="baloon"){
			if(this.prevY!=o.offsetTop){
				this.monitor = 1;
			}
			if(this.monitor == 1 && this.prevY==o.offsetTop){
				this.monitor = 0;
				//this.nowObj = o.offsetTop;
				//window.status = o.offsetTop;
				if(!this.IsGecko){
					setTimeout(this.fireEvent,500);
				}else{
					setTimeout(this.fireEvent,500);
				}
			}
			this.prevY = o.offsetTop;
		}
		if(o.style.position=='absolute')return y;
		while(o=o.offsetParent){
			y+=o.offsetTop;
		}
		return y;
	},
	fireEvent:function(){
		//window.status = this.prevY;
		//window.status = document.getElementById("baloon").offsetTop;
		changeColor(document.getElementById("baloon").offsetTop);
	},
	IsGecko:function(){
		if(navigator){
			if(navigator.userAgent){
				if(navigator.userAgent.indexOf("Gecko/") != -1){
					 return true;
				}
			}
		}
		return false;
	}

};