/**
 * divタグ内の スムーススクロールクラス
 **/
var SmoothScroll = {};
SmoothScroll = {
	targetScrollTop : 0,	// we're gonna make the $(parentid).scrollTop -> targetScrollTop
	dist : 0,
	timer : 0,
	count : 0,
	parentid : 0,
	lastDist : 0,
	//speedStore : [],		// for debug
	options : {},
	defaultOptions : {
		time : 1*1000,	// [ms]
		unit : 50			// [ms]
	},
	scrollTo : function( element, parent_e, options ){
		this.options.time = this.defaultOptions.time;
		this.options.unit = this.defaultOptions.unit;
		if( options ){
			this.options.time = ( options.time ) ? options.time : this.options.time;
			this.options.unit = ( options.unit ) ? options.unit : this.options.unit;
		}
		clearInterval( this.timer );
		this.parentid = parent_e;

		this.scrollTopMax = $(parent_e).scrollHeight - $(parent_e).offsetHeight + parseInt($(parent_e).style.borderTopWidth) + parseInt($(parent_e).style.borderBottomWidth);

		if( navigator.userAgent.match( "MSIE" ) ){
			this.targetScrollTop = ( element ) ? $(element).offsetTop : 0;
		}else{
			var targetOffsetTop = ( element ) ? $(element).offsetTop : $(parent_e).offsetTop;
			this.targetScrollTop = targetOffsetTop - $(parent_e).offsetTop;
		}
		this.targetScrollTop = ( this.targetScrollTop > this.scrollTopMax ) ? this.scrollTopMax : this.targetScrollTop;

		this.dist = this.targetScrollTop - $(parent_e).scrollTop;
		this.lastDist = 0;
		this.timer = setInterval('SmoothScroll.update()', this.options.unit );
		this.count = 0;
		//this.speedStore = [];
		this.update();
	},
	update : function(){
		var dist = this.targetScrollTop - $(this.parentid).scrollTop;
		var speed = 2 * dist * this.options.unit / ( this.options.time - this.options.unit * this.count );
		//this.speedStore.push( speed );
		speed = ( speed > 0 ) ? Math.ceil( speed ) : Math.floor( speed );
		if( Math.abs(dist) <= Math.abs(speed) ){
			// got there
			clearInterval( this.timer );
			$(this.parentid).scrollTop = this.targetScrollTop;
			return;
		}else if( this.lastDist == dist ){
			// stuck
			clearInterval( this.timer );
			$(this.parentid).scrollTop = this.targetScrollTop;
			return;
		}
		var scrollTop = $(this.parentid).scrollTop + speed;
		$(this.parentid).scrollTop = scrollTop;
		this.lastDist = dist;
		this.count++;
		if( this.count == this.options.time / this.options.unit ){
			// timeout
			clearInterval( this.timer );
			$(this.parentid).scrollTop = this.targetScrollTop;
		}
	},
	$ : function(id) {
		return document.getElementById(id);
	}
}