/*
date.js: useful extensions to the JavaScript Date object.
Copyright (C) 1999-2000 Jan Wessely <info@jawe.net>

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
Version 2 as published by the Free Software Foundation.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA
or browse to http://www.gnu.org/copyleft/gpl.html.

created: 25 June 1998
last modified: 17 Jan 2000
*/

// literals *******************************************************************

// used as param unit in Date.add()
Date.MILLI = 1;
Date.SECOND = Date.MILLI * 1000;
Date.MINUTE = Date.SECOND * 60;
Date.HOUR = Date.MINUTE * 60;
Date.DAY = Date.HOUR * 24;
Date.MONTH = -1;
Date.YEAR = -2;

Date.DAYS_IN_MONTH = new Array(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);

// methods ********************************************************************

function _Date_toCanonString()
{
	return this.getFullYear() +
			 _pad(this.getMonth() + 1) + 
			 _pad(this.getDate());
}

function _Date_getFullYear()
{
	var y = this.getYear();
	if(y < 100 && y > 0)
		y += 1900;
	return y;
}

function _Date_setFullYear(val)
{
	this.setYear(val);
}

function _Date_compareTo(other)
{
	return Date.compare(this, other);
}

function _Date_isLeapYear()
{
	return Date.leapYear(this.getFullYear());
}

function _Date_add(date, unit, amount)
{
	return Date.addDate(this, date, unit, amount);
}

function _Date_getDaysInMonth()
{
	return Date.daysInMonth(this.getFullYear(), this.getMonth());
}

// utility functions **********************************************************

function _isLeapYear(year)
{
	return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
}

function _compareDate(d1, d2)
{
	return (new Date(d1)).getTime() - (new Date(d2)).getTime();
}

function _addDate(date, unit, amount)
{
	if(unit == Date.MONTH)
		date.setMonth(date.getMonth() + amount);
	else if(unit == Date.YEAR)
		date.setFullYear(date.getFullYear() + amount);
	else
		date.setTime(date.getTime() + unit * amount);
	return date;
}

function _getDaysInMonth(year, month)
{
	return month == 1 && Date.leapYear(year) ? 29 : Date.DAYS_IN_MONTH[month];
}

function _pad(n)
{
	return (n < 10 ? "0" : "") + n;
}

// initialization *************************************************************

Date.prototype.toCanonString = _Date_toCanonString;
if(!Date.prototype.getFullYear)
{
	Date.prototype.getFullYear = _Date_getFullYear;
	Date.prototype.setFullYear = _Date_setFullYear;
}
Date.prototype.isLeapYear = _Date_isLeapYear;
Date.prototype.compareTo = _Date_compareTo;
Date.prototype.add = _Date_add;
Date.prototype.getDaysInMonth = _Date_getDaysInMonth;

Date.leapYear = _isLeapYear;
Date.compare = _compareDate;
Date.addDate = _addDate;
Date.daysInMonth = _getDaysInMonth;