fc.addDays = addDays;
fc.cloneDate = cloneDate;
fc.parseDate = parseDate;
fc.parseISO8601 = parseISO8601;
fc.parseTime = parseTime;
fc.formatDate = formatDate;
fc.formatDates = formatDates;



/* Date Math
-----------------------------------------------------------------------------*/

var dayIDs = ['sun', 'mon', 'tue', 'wed', 'thu', 'fri', 'sat'],
	DAY_MS = 86400000,
	HOUR_MS = 3600000,
	MINUTE_MS = 60000;
	

function addYears(d, n, keepTime) {
	d.setFullYear(d.getFullYear() + n);
	if (!keepTime) {
		clearTime(d);
	}
	return d;
}


function addMonths(d, n, keepTime) { // prevents day overflow/underflow
	if (+d) { // prevent infinite looping on invalid dates
		var m = d.getMonth() + n,
			check = cloneDate(d);
		check.setDate(1);
		check.setMonth(m);
		d.setMonth(m);
		if (!keepTime) {
			clearTime(d);
		}
		while (d.getMonth() != check.getMonth()) {
			d.setDate(d.getDate() + (d < check ? 1 : -1));
		}
	}
	return d;
}


function addDays(d, n, keepTime) { // deals with daylight savings
	if (+d) {
		var dd = d.getDate() + n,
			check = cloneDate(d);
		check.setHours(9); // set to middle of day
		check.setDate(dd);
		d.setDate(dd);
		if (!keepTime) {
			clearTime(d);
		}
		fixDate(d, check);
	}
	return d;
}


function fixDate(d, check) { // force d to be on check's YMD, for daylight savings purposes
	if (+d) { // prevent infinite looping on invalid dates
		while (d.getDate() != check.getDate()) {
			d.setTime(+d + (d < check ? 1 : -1) * HOUR_MS);
		}
	}
}


function addMinutes(d, n) {
	d.setMinutes(d.getMinutes() + n);
	return d;
}


function clearTime(d) {
	d.setHours(0);
	d.setMinutes(0);
	d.setSeconds(0); 
	d.setMilliseconds(0);
	return d;
}


function cloneDate(d, dontKeepTime) {
	if (dontKeepTime) {
		return clearTime(new Date(+d));
	}
	return new Date(+d);
}


function zeroDate() { // returns a Date with time 00:00:00 and dateOfMonth=1
	var i=0, d;
	do {
		d = new Date(1970, i++, 1);
	} while (d.getHours()); // != 0
	return d;
}


function skipWeekend(date, inc, excl) {
	inc = inc || 1;
	while (!date.getDay() || (excl && date.getDay()==1 || !excl && date.getDay()==6)) {
		addDays(date, inc);
	}
	return date;
}


function dayDiff(d1, d2) { // d1 - d2
	return Math.round((cloneDate(d1, true) - cloneDate(d2, true)) / DAY_MS);
}


function setYMD(date, y, m, d) {
	if (y !== undefined && y != date.getFullYear()) {
		date.setDate(1);
		date.setMonth(0);
		date.setFullYear(y);
	}
	if (m !== undefined && m != date.getMonth()) {
		date.setDate(1);
		date.setMonth(m);
	}
	if (d !== undefined) {
		date.setDate(d);
	}
}



/* Date Parsing
-----------------------------------------------------------------------------*/


function parseDate(s, ignoreTimezone) { // ignoreTimezone defaults to true
	if (typeof s == 'object') { // already a Date object
		return s;
	}
	if (typeof s == 'number') { // a UNIX timestamp
		return new Date(s * 1000);
	}
	if (typeof s == 'string') {
		if (s.match(/^\d+(\.\d+)?$/)) { // a UNIX timestamp
			return new Date(parseFloat(s) * 1000);
		}
		if (ignoreTimezone === undefined) {
			ignoreTimezone = true;
		}
		return parseISO8601(s, ignoreTimezone) || (s ? new Date(s) : null);
	}
	// TODO: never return invalid dates (like from new Date(<string>)), return null instead
	return null;
}


function parseISO8601(s, ignoreTimezone) { // ignoreTimezone defaults to false
	// derived from http://delete.me.uk/2005/03/iso8601.html
	// TODO: for a know glitch/feature, read tests/issue_206_parseDate_dst.html
	var m = s.match(/^([0-9]{4})(-([0-9]{2})(-([0-9]{2})([T ]([0-9]{2}):([0-9]{2})(:([0-9]{2})(\.([0-9]+))?)?(Z|(([-+])([0-9]{2})(:?([0-9]{2}))?))?)?)?)?$/);
	if (!m) {
		return null;
	}
	var date = new Date(m[1], 0, 1);
	if (ignoreTimezone || !m[13]) {
		var check = new Date(m[1], 0, 1, 9, 0);
		if (m[3]) {
			date.setMonth(m[3] - 1);
			check.setMonth(m[3] - 1);
		}
		if (m[5]) {
			date.setDate(m[5]);
			check.setDate(m[5]);
		}
		fixDate(date, check);
		if (m[7]) {
			date.setHours(m[7]);
		}
		if (m[8]) {
			date.setMinutes(m[8]);
		}
		if (m[10]) {
			date.setSeconds(m[10]);
		}
		if (m[12]) {
			date.setMilliseconds(Number("0." + m[12]) * 1000);
		}
		fixDate(date, check);
	}else{
		date.setUTCFullYear(
			m[1],
			m[3] ? m[3] - 1 : 0,
			m[5] || 1
		);
		date.setUTCHours(
			m[7] || 0,
			m[8] || 0,
			m[10] || 0,
			m[12] ? Number("0." + m[12]) * 1000 : 0
		);
		if (m[14]) {
			var offset = Number(m[16]) * 60 + (m[18] ? Number(m[18]) : 0);
			offset *= m[15] == '-' ? 1 : -1;
			date = new Date(+date + (offset * 60 * 1000));
		}
	}
	return date;
}


function parseTime(s) { // returns minutes since start of day
	if (typeof s == 'number') { // an hour
		return s * 60;
	}
	if (typeof s == 'object') { // a Date object
		return s.getHours() * 60 + s.getMinutes();
	}
	var m = s.match(/(\d+)(?::(\d+))?\s*(\w+)?/);
	if (m) {
		var h = parseInt(m[1], 10);
		if (m[3]) {
			h %= 12;
			if (m[3].toLowerCase().charAt(0) == 'p') {
				h += 12;
			}
		}
		return h * 60 + (m[2] ? parseInt(m[2], 10) : 0);
	}
}



/* Date Formatting
-----------------------------------------------------------------------------*/
// TODO: use same function formatDate(date, [date2], format, [options])


function formatDate(date, format, options) {
	return formatDates(date, null, format, options);
}


function formatDates(date1, date2, format, options) {
	options = options || defaults;
	var date = date1,
		otherDate = date2,
		i, len = format.length, c,
		i2, formatter,
		res = '';
	for (i=0; i<len; i++) {
		c = format.charAt(i);
		if (c == "'") {
			for (i2=i+1; i2<len; i2++) {
				if (format.charAt(i2) == "'") {
					if (date) {
						if (i2 == i+1) {
							res += "'";
						}else{
							res += format.substring(i+1, i2);
						}
						i = i2;
					}
					break;
				}
			}
		}
		else if (c == '(') {
			for (i2=i+1; i2<len; i2++) {
				if (format.charAt(i2) == ')') {
					var subres = formatDate(date, format.substring(i+1, i2), options);
					if (parseInt(subres.replace(/\D/, ''), 10)) {
						res += subres;
					}
					i = i2;
					break;
				}
			}
		}
		else if (c == '[') {
			for (i2=i+1; i2<len; i2++) {
				if (format.charAt(i2) == ']') {
					var subformat = format.substring(i+1, i2);
					var subres = formatDate(date, subformat, options);
					if (subres != formatDate(otherDate, subformat, options)) {
						res += subres;
					}
					i = i2;
					break;
				}
			}
		}
		else if (c == '{') {
			date = date2;
			otherDate = date1;
		}
		else if (c == '}') {
			date = date1;
			otherDate = date2;
		}
		else {
			for (i2=len; i2>i; i2--) {
				if (formatter = dateFormatters[format.substring(i, i2)]) {
					if (date) {
						res += formatter(date, options);
					}
					i = i2 - 1;
					break;
				}
			}
			if (i2 == i) {
				if (date) {
					res += c;
				}
			}
		}
	}
	return res;
};


var dateFormatters = {
	s	: function(d)	{ return d.getSeconds() },
	ss	: function(d)	{ return zeroPad(d.getSeconds()) },
	m	: function(d)	{ return d.getMinutes() },
	mm	: function(d)	{ return zeroPad(d.getMinutes()) },
	h	: function(d)	{ return d.getHours() % 12 || 12 },
	hh	: function(d)	{ return zeroPad(d.getHours() % 12 || 12) },
	H	: function(d)	{ return d.getHours() },
	HH	: function(d)	{ return zeroPad(d.getHours()) },
	d	: function(d)	{ return d.getDate() },
	dd	: function(d)	{ return zeroPad(d.getDate()) },
	ddd	: function(d,o)	{ return o.dayNamesShort[d.getDay()] },
	dddd: function(d,o)	{ return o.dayNames[d.getDay()] },
	M	: function(d)	{ return d.getMonth() + 1 },
	MM	: function(d)	{ return zeroPad(d.getMonth() + 1) },
	MMM	: function(d,o)	{ return o.monthNamesShort[d.getMonth()] },
	MMMM: function(d,o)	{ return o.monthNames[d.getMonth()] },
	yy	: function(d)	{ return (d.getFullYear()+'').substring(2) },
	yyyy: function(d)	{ return d.getFullYear() },
	t	: function(d)	{ return d.getHours() < 12 ? 'a' : 'p' },
	tt	: function(d)	{ return d.getHours() < 12 ? 'am' : 'pm' },
	T	: function(d)	{ return d.getHours() < 12 ? 'A' : 'P' },
	TT	: function(d)	{ return d.getHours() < 12 ? 'AM' : 'PM' },
	u	: function(d)	{ return formatDate(d, "yyyy-MM-dd'T'HH:mm:ss'Z'") },
	S	: function(d)	{
		var date = d.getDate();
		if (date > 10 && date < 20) {
			return 'th';
		}
		return ['st', 'nd', 'rd'][date%10-1] || 'th';
	}
};