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File: date.js
/*
 * Date prototype extensions. Doesn't depend on any
 * other code. Doens't overwrite existing methods.
 *
 * Adds dayNames, abbrDayNames, monthNames and abbrMonthNames static properties and isLeapYear,
 * isWeekend, isWeekDay, getDaysInMonth, getDayName, getMonthName, getDayOfYear, getWeekOfYear,
 * setDayOfYear, addYears, addMonths, addDays, addHours, addMinutes, addSeconds methods
 *
 * Copyright (c) 2006 Jörn Zaefferer and Brandon Aaron (brandon.aaron@gmail.com || http://brandonaaron.net)
 *
 * Additional methods and properties added by Kelvin Luck: firstDayOfWeek, dateFormat, zeroTime, asString, fromString -
 * I've added my name to these methods so you know who to blame if they are broken!
 * 
 * Dual licensed under the MIT and GPL licenses:
 *   http://www.opensource.org/licenses/mit-license.php
 *   http://www.gnu.org/licenses/gpl.html
 *
 */

/**
 * An Array of day names starting with Sunday.
 * 
 * @example dayNames[0]
 * @result 'Sunday'
 *
 * @name dayNames
 * @type Array
 * @cat Plugins/Methods/Date
 */
Date.dayNames = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];

/**
 * An Array of abbreviated day names starting with Sun.
 * 
 * @example abbrDayNames[0]
 * @result 'Sun'
 *
 * @name abbrDayNames
 * @type Array
 * @cat Plugins/Methods/Date
 */
Date.abbrDayNames = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];

/**
 * An Array of month names starting with Janurary.
 * 
 * @example monthNames[0]
 * @result 'January'
 *
 * @name monthNames
 * @type Array
 * @cat Plugins/Methods/Date
 */
Date.monthNames = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'];

/**
 * An Array of abbreviated month names starting with Jan.
 * 
 * @example abbrMonthNames[0]
 * @result 'Jan'
 *
 * @name monthNames
 * @type Array
 * @cat Plugins/Methods/Date
 */
Date.abbrMonthNames = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];

/**
 * The first day of the week for this locale.
 *
 * @name firstDayOfWeek
 * @type Number
 * @cat Plugins/Methods/Date
 * @author Kelvin Luck
 */
Date.firstDayOfWeek = 1;

/**
 * The format that string dates should be represented as (e.g. 'dd/mm/yyyy' for UK, 'mm/dd/yyyy' for US, 'yyyy-mm-dd' for Unicode etc).
 *
 * @name format
 * @type String
 * @cat Plugins/Methods/Date
 * @author Kelvin Luck
 */
Date.format = 'dd/mm/yyyy';
//Date.format = 'mm/dd/yyyy';
//Date.format = 'yyyy-mm-dd';
//Date.format = 'dd mmm yy';

/**
 * The first two numbers in the century to be used when decoding a two digit year. Since a two digit year is ambiguous (and date.setYear
 * only works with numbers < 99 and so doesn't allow you to set years after 2000) we need to use this to disambiguate the two digit year codes.
 *
 * @name format
 * @type String
 * @cat Plugins/Methods/Date
 * @author Kelvin Luck
 */
Date.fullYearStart = '20';

(function() {

	/**
	 * Adds a given method under the given name 
	 * to the Date prototype if it doesn't
	 * currently exist.
	 *
	 * @private
	 */
	function add(name, method) {
		if( !Date.prototype[name] ) {
			Date.prototype[name] = method;
		}
	};
	
	/**
	 * Checks if the year is a leap year.
	 *
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.isLeapYear();
	 * @result true
	 *
	 * @name isLeapYear
	 * @type Boolean
	 * @cat Plugins/Methods/Date
	 */
	add("isLeapYear", function() {
		var y = this.getFullYear();
		return (y%4==0 && y%100!=0) || y%400==0;
	});
	
	/**
	 * Checks if the day is a weekend day (Sat or Sun).
	 *
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.isWeekend();
	 * @result false
	 *
	 * @name isWeekend
	 * @type Boolean
	 * @cat Plugins/Methods/Date
	 */
	add("isWeekend", function() {
		return this.getDay()==0 || this.getDay()==6;
	});
	
	/**
	 * Check if the day is a day of the week (Mon-Fri)
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.isWeekDay();
	 * @result false
	 * 
	 * @name isWeekDay
	 * @type Boolean
	 * @cat Plugins/Methods/Date
	 */
	add("isWeekDay", function() {
		return !this.isWeekend();
	});
	
	/**
	 * Gets the number of days in the month.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.getDaysInMonth();
	 * @result 31
	 * 
	 * @name getDaysInMonth
	 * @type Number
	 * @cat Plugins/Methods/Date
	 */
	add("getDaysInMonth", function() {
		return [31,(this.isLeapYear() ? 29:28),31,30,31,30,31,31,30,31,30,31][this.getMonth()];
	});
	
	/**
	 * Gets the name of the day.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.getDayName();
	 * @result 'Saturday'
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.getDayName(true);
	 * @result 'Sat'
	 * 
	 * @param abbreviated Boolean When set to true the name will be abbreviated.
	 * @name getDayName
	 * @type String
	 * @cat Plugins/Methods/Date
	 */
	add("getDayName", function(abbreviated) {
		return abbreviated ? Date.abbrDayNames[this.getDay()] : Date.dayNames[this.getDay()];
	});

	/**
	 * Gets the name of the month.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.getMonthName();
	 * @result 'Janurary'
	 *
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.getMonthName(true);
	 * @result 'Jan'
	 * 
	 * @param abbreviated Boolean When set to true the name will be abbreviated.
	 * @name getDayName
	 * @type String
	 * @cat Plugins/Methods/Date
	 */
	add("getMonthName", function(abbreviated) {
		return abbreviated ? Date.abbrMonthNames[this.getMonth()] : Date.monthNames[this.getMonth()];
	});

	/**
	 * Get the number of the day of the year.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.getDayOfYear();
	 * @result 11
	 * 
	 * @name getDayOfYear
	 * @type Number
	 * @cat Plugins/Methods/Date
	 */
	add("getDayOfYear", function() {
		var tmpdtm = new Date("1/1/" + this.getFullYear());
		return Math.floor((this.getTime() - tmpdtm.getTime()) / 86400000);
	});
	
	/**
	 * Get the number of the week of the year.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.getWeekOfYear();
	 * @result 2
	 * 
	 * @name getWeekOfYear
	 * @type Number
	 * @cat Plugins/Methods/Date
	 */
	add("getWeekOfYear", function() {
		return Math.ceil(this.getDayOfYear() / 7);
	});

	/**
	 * Set the day of the year.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.setDayOfYear(1);
	 * dtm.toString();
	 * @result 'Tue Jan 01 2008 00:00:00'
	 * 
	 * @name setDayOfYear
	 * @type Date
	 * @cat Plugins/Methods/Date
	 */
	add("setDayOfYear", function(day) {
		this.setMonth(0);
		this.setDate(day);
		return this;
	});
	
	/**
	 * Add a number of years to the date object.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.addYears(1);
	 * dtm.toString();
	 * @result 'Mon Jan 12 2009 00:00:00'
	 * 
	 * @name addYears
	 * @type Date
	 * @cat Plugins/Methods/Date
	 */
	add("addYears", function(num) {
		this.setFullYear(this.getFullYear() + num);
		return this;
	});
	
	/**
	 * Add a number of months to the date object.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.addMonths(1);
	 * dtm.toString();
	 * @result 'Tue Feb 12 2008 00:00:00'
	 * 
	 * @name addMonths
	 * @type Date
	 * @cat Plugins/Methods/Date
	 */
	add("addMonths", function(num) {
		var tmpdtm = this.getDate();
		
		this.setMonth(this.getMonth() + num);
		
		if (tmpdtm > this.getDate())
			this.addDays(-this.getDate());
		
		return this;
	});
	
	/**
	 * Add a number of days to the date object.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.addDays(1);
	 * dtm.toString();
	 * @result 'Sun Jan 13 2008 00:00:00'
	 * 
	 * @name addDays
	 * @type Date
	 * @cat Plugins/Methods/Date
	 */
	add("addDays", function(num) {
		this.setDate(this.getDate() + num);
		return this;
	});
	
	/**
	 * Add a number of hours to the date object.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.addHours(24);
	 * dtm.toString();
	 * @result 'Sun Jan 13 2008 00:00:00'
	 * 
	 * @name addHours
	 * @type Date
	 * @cat Plugins/Methods/Date
	 */
	add("addHours", function(num) {
		this.setHours(this.getHours() + num);
		return this;
	});

	/**
	 * Add a number of minutes to the date object.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.addMinutes(60);
	 * dtm.toString();
	 * @result 'Sat Jan 12 2008 01:00:00'
	 * 
	 * @name addMinutes
	 * @type Date
	 * @cat Plugins/Methods/Date
	 */
	add("addMinutes", function(num) {
		this.setMinutes(this.getMinutes() + num);
		return this;
	});
	
	/**
	 * Add a number of seconds to the date object.
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.addSeconds(60);
	 * dtm.toString();
	 * @result 'Sat Jan 12 2008 00:01:00'
	 * 
	 * @name addSeconds
	 * @type Date
	 * @cat Plugins/Methods/Date
	 */
	add("addSeconds", function(num) {
		this.setSeconds(this.getSeconds() + num);
		return this;
	});
	
	/**
	 * Sets the time component of this Date to zero for cleaner, easier comparison of dates where time is not relevant.
	 * 
	 * @example var dtm = new Date();
	 * dtm.zeroTime();
	 * dtm.toString();
	 * @result 'Sat Jan 12 2008 00:01:00'
	 * 
	 * @name zeroTime
	 * @type Date
	 * @cat Plugins/Methods/Date
	 * @author Kelvin Luck
	 */
	add("zeroTime", function() {
		this.setMilliseconds(0);
		this.setSeconds(0);
		this.setMinutes(0);
		this.setHours(0);
		return this;
	});
	
	/**
	 * Returns a string representation of the date object according to Date.format.
	 * (Date.toString may be used in other places so I purposefully didn't overwrite it)
	 * 
	 * @example var dtm = new Date("01/12/2008");
	 * dtm.asString();
	 * @result '12/01/2008' // (where Date.format == 'dd/mm/yyyy'
	 * 
	 * @name asString
	 * @type Date
	 * @cat Plugins/Methods/Date
	 * @author Kelvin Luck
	 */
	add("asString", function() {
		var r = Date.format;
		return r
			.split('yyyy').join(this.getFullYear())
			.split('yy').join((this.getFullYear() + '').substring(2))
			.split('mmm').join(this.getMonthName(true))
			.split('mm').join(_zeroPad(this.getMonth()+1))
			.split('dd').join(_zeroPad(this.getDate()));
	});
	
	/**
	 * Returns a new date object created from the passed String according to Date.format or false if the attempt to do this results in an invalid date object
	 * (We can't simple use Date.parse as it's not aware of locale and I chose not to overwrite it incase it's functionality is being relied on elsewhere)
	 *
	 * @example var dtm = Date.fromString("12/01/2008");
	 * dtm.toString();
	 * @result 'Sat Jan 12 2008 00:00:00' // (where Date.format == 'dd/mm/yyyy'
	 * 
	 * @name fromString
	 * @type Date
	 * @cat Plugins/Methods/Date
	 * @author Kelvin Luck
	 */
	Date.fromString = function(s)
	{
		var f = Date.format;
		var d = new Date('01/01/1977');
		var iY = f.indexOf('yyyy');
		if (iY > -1) {
			d.setFullYear(Number(s.substr(iY, 4)));
		} else {
			// TODO - this doesn't work very well - are there any rules for what is meant by a two digit year?
			d.setFullYear(Number(Date.fullYearStart + s.substr(f.indexOf('yy'), 2)));
		}
		var iM = f.indexOf('mmm');
		if (iM > -1) {
			var mStr = s.substr(iM, 3);
			for (var i=0; i<Date.abbrMonthNames.length; i++) {
				if (Date.abbrMonthNames[i] == mStr) break;
			}
			d.setMonth(i);
		} else {
			d.setMonth(Number(s.substr(f.indexOf('mm'), 2)) - 1);
		}
		d.setDate(Number(s.substr(f.indexOf('dd'), 2)));
		if (isNaN(d.getTime())) {
			return false;
		}
		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 :(
	};
	
})();