Date.dayNames = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
Date.abbrDayNames = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];
Date.monthNames = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'];
Date.abbrMonthNames = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
Date.firstDayOfWeek = 1;
Date.format = 'mm/dd/yyyy';
Date.fullYearStart = '20';

(function() {
	function add(name, method) {
		if( !Date.prototype[name] ) {
			Date.prototype[name] = method;
		}
	};
	add("isLeapYear", function() {
		var y = this.getFullYear();
		return (y%4==0 && y%100!=0) || y%400==0;
	});
	add("isWeekend", function() {
		return this.getDay()==0 || this.getDay()==6;
	});
	add("isWeekDay", function() {
		return !this.isWeekend();
	});
	add("getDaysInMonth", function() {
		return [31,(this.isLeapYear() ? 29:28),31,30,31,30,31,31,30,31,30,31][this.getMonth()];
	});
	
	add("getDayName", function(abbreviated) {
		return abbreviated ? Date.abbrDayNames[this.getDay()] : Date.dayNames[this.getDay()];
	});
	add("getMonthName", function(abbreviated) {
		return abbreviated ? Date.abbrMonthNames[this.getMonth()] : Date.monthNames[this.getMonth()];
	});

	add("getDayOfYear", function() {
		var tmpdtm = new Date("1/1/" + this.getFullYear());
		return Math.floor((this.getTime() - tmpdtm.getTime()) / 86400000);
	});
	
	add("getWeekOfYear", function() {
		return Math.ceil(this.getDayOfYear() / 7);
	});
	add("setDayOfYear", function(day) {
		this.setMonth(0);
		this.setDate(day);
		return this;
	});
	add("addYears", function(num) {
		this.setFullYear(this.getFullYear() + num);
		return this;
	});
	
	add("addMonths", function(num) {
		var tmpdtm = this.getDate();
		
		this.setMonth(this.getMonth() + num);
		
		if (tmpdtm > this.getDate())
			this.addDays(-this.getDate());
		
		return this;
	});
	add("addDays", function(num) {
		//this.setDate(this.getDate() + num);
		this.setTime(this.getTime() + (num*86400000) );
		return this;
	});
	add("addHours", function(num) {
		this.setHours(this.getHours() + num);
		return this;
	});
	add("addMinutes", function(num) {
		this.setMinutes(this.getMinutes() + num);
		return this;
	});
	
	add("addSeconds", function(num) {
		this.setSeconds(this.getSeconds() + num);
		return this;
	});
	
	add("zeroTime", function() {
		this.setMilliseconds(0);
		this.setSeconds(0);
		this.setMinutes(0);
		this.setHours(0);
		return this;
	});
	add("asString", function(format) {
		var r = format || Date.format;
		if (r.split('mm').length>1) { // ugly workaround to make sure we don't replace the m's in e.g. noveMber
			r = r.split('mmmm').join(this.getMonthName(false))
				.split('mmm').join(this.getMonthName(true))
				.split('mm').join(_zeroPad(this.getMonth()+1))
		} else {
			r = r.split('m').join(this.getMonth()+1);
		}
		r = r.split('yyyy').join(this.getFullYear())
			.split('yy').join((this.getFullYear() + '').substring(2))
			.split('dd').join(_zeroPad(this.getDate()))
			.split('d').join(this.getDate());
		return r;
	});
	
	Date.fromString = function(s)
	{
		var f = Date.format;
		
		var d = new Date('01/01/1970');
		
		if (s == '') return d;

		s = s.toLowerCase();
		var matcher = '';
		var order = [];
		var r = /(dd?d?|mm?m?|yy?yy?)+([^(m|d|y)])?/g;
		var results;
		while ((results = r.exec(f)) != null)
		{
			switch (results[1]) {
				case 'd':
				case 'dd':
				case 'm':
				case 'mm':
				case 'yy':
				case 'yyyy':
					matcher += '(\\d+\\d?\\d?\\d?)+';
					order.push(results[1].substr(0, 1));
					break;
				case 'mmm':
					matcher += '([a-z]{3})';
					order.push('M');
					break;
			}
			if (results[2]) {
				matcher += results[2];
			}
			
		}
		var dm = new RegExp(matcher);
		var result = s.match(dm);
		for (var i=0; i<order.length; i++) {
			var res = result[i+1];
			switch(order[i]) {
				case 'd':
					d.setDate(res);
					break;
				case 'm':
					d.setMonth(Number(res)-1);
					break;
				case 'M':
					for (var j=0; j<Date.abbrMonthNames.length; j++) {
						if (Date.abbrMonthNames[j].toLowerCase() == res) break;
					}
					d.setMonth(j);
					break;
				case 'y':
					d.setYear(res);
					break;
			}
		}

		return d;
	};
	
	// utility method
	var _zeroPad = function(num) {
		var s = '0'+num;
		return s.substring(s.length-2)
		//return ('0'+num).substring(-2); // doesn't work on IE :(
	};
	
})();