/* Get time intervals between two Dates v2.0
 * 
 * This work is licensed under a Creative Commons Attribution 3.0 Unported License
 * http://creativecommons.org/licenses/by/3.0/
 *
 * Author: Andy Harrison, http://dragonzreef.com/
 * Date: 16 September 2011
 */
 
Date.isLeapYear = function(year){ return (year%400 == 0 || (year%4 == 0 && year%100 != 0)); }
Date.prototype.isLeapYear = function(){ return Date.isLeapYear(this.getFullYear()); }
 
//get the number of days in a given month of a given year (month being 0-11)
Date.daysInMonth = function(year, month){ return ([31, (Date.isLeapYear(year)?29:28), 31,30,31,30,31,31,30,31,30,31])[month]; }
Date.prototype.daysInMonth = function(){ return Date.daysInMonth(this.getFullYear(), this.getMonth()); }
 
//returns an object with time intervals between two Dates
//Date objects, milliseconds, or date strings are accepted arguments
//object properties: years, months, weeks, days, hours, minutes, seconds, milliseconds
//each part is *in addition* to the sum of the larger parts; e.g., if there are 17 days between the two dates, .weeks==2 and .days==3
Date.timeBetween = function(dateA, dateB)
{
	dateA = new Date(dateA);
	dateB = new Date(dateB);
	if(isNaN(dateA.valueOf()+dateB.valueOf())) return null;	//invalid date(s)
 
	if(dateA.valueOf() > dateB.valueOf())
	{
		var tmp = dateA;
		dateA = dateB;
		dateB = tmp;
	}
 
	var parts = {};
 
	//years
	parts.years = dateB.getFullYear() - dateA.getFullYear();
 
	//months
	dateA.setFullYear(dateB.getFullYear());
	parts.months = dateB.getMonth() - dateA.getMonth();
 
	//days
	dateA.setMonth(dateB.getMonth());
	if(dateA.valueOf() > dateB.valueOf())
	{
		dateA.setMonth(dateA.getMonth()-1);
		parts.months--;
	}
	parts.days = Math.floor((dateB.valueOf()-dateA.valueOf())/86400000);
 
	//time
	parts.hours = dateB.getHours() - dateA.getHours();
	parts.minutes = dateB.getMinutes() - dateA.getMinutes();
	parts.seconds = dateB.getSeconds() - dateA.getSeconds();
	parts.milliseconds = dateB.getMilliseconds() - dateA.getMilliseconds();
 
	//weeks
	parts.weeks = Math.floor(parts.days/7);
	parts.days = parts.days%7;
 
	//adjust for negative values
	if(parts.milliseconds < 0){ parts.milliseconds = 1000+parts.milliseconds; parts.seconds--; }
	if(parts.seconds < 0){ parts.seconds = 60+parts.seconds; parts.minutes--; }
	if(parts.minutes < 0){ parts.minutes = 60+parts.minutes; parts.hours--; }
	if(parts.hours < 0) parts.hours = 24+parts.hours;
	if(parts.months < 0){ parts.months = 12+parts.months; parts.years--; }
 
	return parts;
}