/**
	@method timeSpan
	@param fromDate {Date} The starting date.
	@param toDate {Date} The ending date.
	@param format {String} A comma separated list of the formats to return, from greatest to least (years > months > weeks > days > hours > minutes > seconds > milliseconds).
	@sample timeSpan(new Date(2009,12,12), new Date(2008,1,12), "months,weeks,days");
	@author Stephen Rushing		
*/

tbelt.util.timeSpan=function(fromDate, toDate, format){
	if(format==null) format="milliseconds";	
	var formatsMS = {
		milliseconds:1,
		seconds:1000,
		minutes:1000*60,
		hours:1000*60*60,
		days:1000*60*60*24,
		weeks:1000*60*60*24*7,
		months:function(m){
			var ms = this.days,
			daysPer = [ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ];
			return ms*daysPer[m];
		},
		years:function(y){
			var ms = 1000*60*60*24*365;
			//add a day for leap years
			if( (y % 4 == 0 && y % 100 == 0) || y % 400 == 0 )
				ms += this.days;
			return ms;
		}
	},
	//get the time difference in milliseconds
	ms = toDate.getTime()-fromDate.getTime(),
	reqFormats = format.split(","),
	isYearReq = (format.indexOf("years")>-1),
	isMonthReq = (format.indexOf("months")>-1),
	result = {};
	
	if(isYearReq){ 
		result["years"]=0;
		for(var y=fromDate.getFullYear(); y <= toDate.getFullYear(); y++){	
			var yearMS = formatsMS.years(y);
			if(ms >= yearMS){
				ms -= yearMS;
				result["years"]+=1;
			}
		}
		//use "to" year for calculating decimal
		formatsMS.years = formatsMS.years(toDate.getFullYear());
	}
	if(isMonthReq){
		result["months"]=0;
		var month = fromDate.getMonth(),
			year = (result["years"]>0) ? fromDate.getFullYear() + result["years"] : fromDate.getFullYear();					
		for(month; month<=11; month++){
			var monthMS = formatsMS.months(month);
			if(month==toDate.getMonth() && year== toDate.getFullYear()) break;
			else if(ms >= monthMS){
				ms -= monthMS;
				result["months"]+=1;
			}
			if(month==12 && year < toDate.getFullYear()) {
				month=0; 
				year++;
			}
		}
		//use "to" month for decimal
		formatsMS.months = formatsMS.months(toDate.getMonth());
	}

	//handle the remaining milliseconds
	for(var f=0; f < reqFormats.length && reqFormats[0]!=""; f++){
		var res=(f<reqFormats.length-1) ? Math.floor(ms/formatsMS[reqFormats[f]]) : ms/formatsMS[reqFormats[f]];
		if(ms>0) result[reqFormats[f]] = (result[reqFormats[f]]>=0) ? result[reqFormats[f]]+=res : res;
		else result[reqFormats[f]]=0;

		ms -= res * formatsMS[reqFormats[f]];
	}
	return result;
}