Calc.php

<?php

// The constant telling us what day starts the week. Monday (1) is the
// international standard. Redefine this to 0 if you want weeks to
// begin on Sunday.
//define('DATE_CALC_BEGIN_WEEKDAY', 1);

/**
 * Date_Calc is a calendar class used to calculate and
 * manipulate calendar dates and retrieve dates in a calendar
 * format. It does not rely on 32-bit system date stamps, so
 * you can display calendars and compare dates that date
 * pre 1970 and post 2038.
 *
 * This source file is subject to version 2.02 of the PHP license,
 * that is bundled with this package in the file LICENSE, and is
 * available at through the world-wide-web at
 * http://www.php.net/license/2_02.txt.
 * If you did not receive a copy of the PHP license and are unable to
 * obtain it through the world-wide-web, please send a note to
 * license@php.net so we can mail you a copy immediately.
 *
 * Copyright (c) 1999, 2000 ispi
 *
 * @access public
 *
 * @version 1.2.5
 * @author Monte Ohrt <monte@ispi.net>
 */

class Date_Calc {

    /**
     * Returns the current local date. NOTE: This function
     * retrieves the local date using strftime(), which may
     * or may not be 32-bit safe on your system.
     *
     * @param string the strftime() format to return the date
     *
     * @access public
     *
     * @return string the current date in specified format
     */

    static function dateNow($format="%Y%m%d")
    {
        return(strftime($format,time()));

    } // end func dateNow

     /**
     * Returns true for valid date, false for invalid date.
     *
     * @param string year in format CCYY
     * @param string month in format MM
     * @param string day in format DD
     *
     * @access public
     *
     * @return boolean true/false
     */

    static function isValidDate($day, $month, $year)
    {

        if(empty($year) || empty($month) || empty($day))
            return false;

        // must be digits only
        if(preg_match("/\D/",$year))
            return false;
        if(preg_match("/\D/",$month))
            return false;
        if(preg_match("/\D/",$day))
            return false;

        if($year < 0 || $year > 9999)
            return false;
        if($month < 1 || $month > 12)
            return false;
        if($day < 1 || $day > 31 || $day > Date_Calc::daysInMonth($month,$year))
            return false;

        return true;

    } // end func isValidDate

    static function isLeapYear($year="")
    {

        if(empty($year))
            $year = Date_Calc::dateNow("%Y");

        if(strlen($year) != 4)
            return false;

        if(preg_match("/\D/",$year))
            return false;

        return (($year % 4 == 0 && $year % 100 != 0) || $year % 400 == 0);

    } // end func isLeapYear

    /**
     * Determines if given date is a future date from now.
     *
     * @param string year in format CCYY
     * @param string month in format MM
     * @param string day in format DD
     *
     * @access public
     *
     * @return boolean true/false
     */

    static function isFutureDate($day,$month,$year)
    {
        $this_year = Date_Calc::dateNow("%Y");
        $this_month = Date_Calc::dateNow("%m");
        $this_day = Date_Calc::dateNow("%d");


        if($year > $this_year)
            return true;
        elseif($year == $this_year)
            if($month > $this_month)
                return true;
            elseif($month == $this_month)
                if($day > $this_day)
                    return true;

        return false;

    } // end func isFutureDate

    /**
     * Determines if given date is a past date from now.
     *
     * @param string year in format CCYY
     * @param string month in format MM
     * @param string day in format DD
     *
     * @access public
     *
     * @return boolean true/false
     */

    static function isPastDate($day,$month,$year)
    {
        $this_year = Date_Calc::dateNow("%Y");
        $this_month = Date_Calc::dateNow("%m");
        $this_day = Date_Calc::dateNow("%d");


        if($year < $this_year)
            return true;
        elseif($year == $this_year)
            if($month < $this_month)
                return true;
            elseif($month == $this_month)
                if($day < $this_day)
                    return true;

        return false;

    } // end func isPastDate

    /**
     * Returns day of week for given date, 0=Sunday
     *
     * @param string year in format CCYY, default is current local year
     * @param string month in format MM, default is current local month
     * @param string day in format DD, default is current local day
     *
     * @access public
     *
     * @return int $weekday_number
     */

    static function dayOfWeek($day="",$month="",$year="")
    {

        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        if($month > 2)
            $month -= 2;
        else
        {
            $month += 10;
            $year--;
        }

        $day =     ( floor((13 * $month - 1) / 5) +
                $day + ($year % 100) +
                floor(($year % 100) / 4) +
                floor(($year / 100) / 4) - 2 *
                floor($year / 100) + 77);

        $weekday_number = (($day - 7 * floor($day / 7)));

        return $weekday_number;

    } // end func dayOfWeek

    /**
     * Returns week of the year, first Sunday is first day of first week
     *
     * @param string day in format DD
     * @param string month in format MM
     * @param string year in format CCYY
     *
     * @access public
     *
     * @return integer $week_number
     */

    static function weekOfYear($day,$month,$year)
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $week_year = $year - 1501;
        $week_day = $week_year * 365 + floor($week_year / 4) - 29872 + 1
                - floor($week_year / 100) + floor(($week_year - 300) / 400);

        $week_number =
                ceil((Date_Calc::julianDate($day,$month,$year) + floor(($week_day + 4) % 7)) / 7);

        return $week_number;

    } // end func weekOfYear

    /**
     * Returns number of days since 31 December of year before given date.
     *
     * @param string year in format CCYY, default is current local year
     * @param string month in format MM, default is current local month
     * @param string day in format DD, default is current local day
     *
     * @access public
     *
     * @return int $julian
     */

    static function julianDate($day="",$month="",$year="")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $days = array(0,31,59,90,120,151,181,212,243,273,304,334);

        $julian = ($days[$month - 1] + $day);

        if($month > 2 && Date_Calc::isLeapYear($year))
            $julian++;

        return($julian);

    } // end func julianDate

    /**
     * Returns quarter of the year for given date
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     *
     * @access public
     *
     * @return int $year_quarter
     */

    static function quarterOfYear($day="",$month="",$year="")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $year_quarter = (intval(($month - 1) / 3 + 1));

        return $year_quarter;

    } // end func quarterOfYear

    /**
     * Returns date of begin of next month of given date.
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function beginOfNextMonth($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        if($month < 12)
        {
            $month++;
            $day=1;
        }
        else
        {
            $year++;
            $month=1;
            $day=1;
        }

        return Date_Calc::dateFormat($day,$month,$year,$format);

    } // end func beginOfNextMonth

    /**
     * Returns date of the last day of next month of given date.
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function endOfNextMonth($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");


        if($month < 12)
        {
            $month++;
        }
        else
        {
            $year++;
            $month=1;
        }

        $day = Date_Calc::daysInMonth($month,$year);

        return Date_Calc::dateFormat($day,$month,$year,$format);

    } // end func endOfNextMonth

    /**
     * Returns date of the first day of previous month of given date.
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function beginOfPrevMonth($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        if($month > 1)
        {
            $month--;
            $day=1;
        }
        else
        {
            $year--;
            $month=12;
            $day=1;
        }

        return Date_Calc::dateFormat($day,$month,$year,$format);

    } // end func beginOfPrevMonth

    /**
     * Returns date of the last day of previous month for given date.
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function endOfPrevMonth($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        if($month > 1)
        {
            $month--;
        }
        else
        {
            $year--;
            $month=12;
        }

        $day = Date_Calc::daysInMonth($month,$year);

        return Date_Calc::dateFormat($day,$month,$year,$format);

    } // end func endOfPrevMonth

    /**
     * Returns date of the next weekday of given date,
     * skipping from Friday to Monday.
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function nextWeekday($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $days = Date_Calc::dateToDays($day,$month,$year);

        if(Date_Calc::dayOfWeek($day,$month,$year) == 5)
            $days += 3;
        elseif(Date_Calc::dayOfWeek($day,$month,$year) == 6)
            $days += 2;
        else
            $days += 1;

        return(Date_Calc::daysToDate($days,$format));

    } // end func nextWeekday

    /**
     * Returns date of the previous weekday,
     * skipping from Monday to Friday.
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function prevWeekday($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $days = Date_Calc::dateToDays($day,$month,$year);

        if(Date_Calc::dayOfWeek($day,$month,$year) == 1)
            $days -= 3;
        elseif(Date_Calc::dayOfWeek($day,$month,$year) == 0)
            $days -= 2;
        else
            $days -= 1;

        return(Date_Calc::daysToDate($days,$format));

    } // end func prevWeekday

    /**
     * Returns date of the next specific day of the week
     * from the given date.
     *
     * @param int day of week, 0=Sunday
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param boolean onOrAfter if true and days are same, returns current day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function nextDayOfWeek($dow,$day="",$month="",$year="",$format="%Y%m%d",$onOrAfter=false)
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $days = Date_Calc::dateToDays($day,$month,$year);
        $curr_weekday = Date_Calc::dayOfWeek($day,$month,$year);

        if($curr_weekday == $dow)
		{
			if(!$onOrAfter)
            	$days += 7;
		}
        elseif($curr_weekday > $dow)
            $days += 7 - ( $curr_weekday - $dow );
        else
            $days += $dow - $curr_weekday;

        return(Date_Calc::daysToDate($days,$format));

    } // end func nextDayOfWeek

    /**
     * Returns date of the previous specific day of the week
     * from the given date.
     *
     * @param int day of week, 0=Sunday
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param boolean onOrBefore if true and days are same, returns current day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function prevDayOfWeek($dow,$day="",$month="",$year="",$format="%Y%m%d",$onOrBefore=false)
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $days = Date_Calc::dateToDays($day,$month,$year);
        $curr_weekday = Date_Calc::dayOfWeek($day,$month,$year);

        if($curr_weekday == $dow)
		{
			if(!$onOrBefore)
            	$days -= 7;
		}
        elseif($curr_weekday < $dow)
            $days -= 7 - ( $dow - $curr_weekday );
        else
            $days -= $curr_weekday - $dow;

        return(Date_Calc::daysToDate($days,$format));

    } // end func prevDayOfWeek

    /**
     * Returns date of the next specific day of the week
     * on or before the given date.
     *
     * @param int day of week, 0=Sunday
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function nextDayOfWeekOnOrAfter($dow,$day="",$month="",$year="",$format="%Y%m%d")
    {
        return(Date_Calc::nextDayOfWeek($dow,$day="",$month="",$year="",$format="%Y%m%d",true));
    } // end func nextDayOfWeekOnOrAfter

    /**
     * Returns date of the previous specific day of the week
     * on or before the given date.
     *
     * @param int day of week, 0=Sunday
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function prevDayOfWeekOnOrBefore($dow,$day="",$month="",$year="",$format="%Y%m%d")
    {
        return(Date_Calc::prevDayOfWeek($dow,$day="",$month="",$year="",$format="%Y%m%d",true));

    } // end func prevDayOfWeekOnOrAfter

    /**
     * Returns date of day after given date.
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function nextDay($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $days = Date_Calc::dateToDays($day,$month,$year);

        return(Date_Calc::daysToDate($days + 1,$format));

    } // end func nextDay

    /**
     * Returns date of day before given date.
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function prevDay($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $days = Date_Calc::dateToDays($day,$month,$year);

        return(Date_Calc::daysToDate($days - 1,$format));

    } // end func prevDay

    /**
     * Sets century for 2 digit year.
     * 51-99 is 19, else 20
     *
     * @param string 2 digit year
     *
     * @access public
     *
     * @return string 4 digit year
     */

    static function defaultCentury($year)
    {
        if(strlen($year) == 1)
            $year = "0$year";
        if($year > 50)
            return( "19$year" );
        else
            return( "20$year" );

    } // end func defaultCentury

    /**
     * Returns number of days between two given dates.
     *
     * @param string year in format CCYY
     * @param string month in format MM
     * @param string day in format DD
     * @param string year in format CCYY
     * @param string month in format MM
     * @param string day in format DD
     *
     * @access public
     *
     * @return int absolute number of days between dates,
     *      -1 if there is an error.
     */

    static function dateDiff($day1,$month1,$year1,$day2,$month2,$year2)
    {
        if(!Date_Calc::isValidDate($day1,$month1,$year1))
            return -1;
        if(!Date_Calc::isValidDate($day2,$month2,$year2))
            return -1;

        return(abs((Date_Calc::dateToDays($day1,$month1,$year1))
                    - (Date_Calc::dateToDays($day2,$month2,$year2))));

    } // end func dateDiff

    /**
     * Find the number of days in the given month.
     *
     * @param string month in format MM, default current local month
     *
     * @access public
     *
     * @return int number of days
     */

    static function daysInMonth($month="",$year="")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");

        if($month == 2)
        {
            if(Date_Calc::isLeapYear($year))
                return 29;
            else
                return 28;
        }
        elseif($month == 4 or $month == 6 or $month == 9 or $month == 11)
            return 30;
        else
            return 31;

    } // end func daysInMonth

    /**
     * Returns the number of rows on a calendar month. Useful for
     * determining the number of rows when displaying a typical
     * month calendar.
     *
     * @param string month in format MM, default current local month
     * @param string year in format YYCC, default current local year
     *
     * @access public
     *
     * @return int number of weeks
     */

    static function weeksInMonth($month="",$year="")
    {
        if(empty($year)) {
            $year = Date_Calc::dateNow("%Y");
		}
        if(empty($month)) {
            $month = Date_Calc::dateNow("%m");
		}
		// starts on monday
		if(DATE_CALC_BEGIN_WEEKDAY == 1)
		{	if(Date_Calc::firstOfMonthWeekday($month,$year) == 0) {
				$first_week_days = 1;
			} else {
				$first_week_days = 7 - (Date_Calc::firstOfMonthWeekday($month,$year) - 1);
			}
		// starts on saturday
		} elseif(DATE_CALC_BEGIN_WEEKDAY == 6) {	
			if(Date_Calc::firstOfMonthWeekday($month,$year) == 0) {
				$first_week_days = 6;
			} else {
				$first_week_days = 7 - (Date_Calc::firstOfMonthWeekday($month,$year) + 1);
			}
		// starts on sunday
		} else {
			$first_week_days = 7 - Date_Calc::firstOfMonthWeekday($month,$year);
		}
		return ceil(((Date_Calc::daysInMonth($month,$year) - $first_week_days) / 7) + 1);
	} // end func weeksInMonth

    /**
     * Find the day of the week for the first of the month of given date.
     *
     * @param string year in format CCYY, default to current local year
     * @param string month in format MM, default to current local month
     *
     * @access public
     *
     * @return int number of weekday for the first day, 0=Sunday
     */

    static function firstOfMonthWeekday($month="",$year="")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");

        return(Date_Calc::dayOfWeek("01",$month,$year));

    } // end func firstOfMonthWeekday

    /**
     * Return date of first day of month of given date.
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function beginOfMonth($month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");

        return(Date_Calc::dateFormat("01",$month,$year,$format));

    } // end of func beginOfMonth

    /**
     * Find the month day of the beginning of week for given date,
     * using DATE_CALC_BEGIN_WEEKDAY. (can return weekday of prev month.)
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function beginOfWeek($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $this_weekday = Date_Calc::dayOfWeek($day,$month,$year);

	if(DATE_CALC_BEGIN_WEEKDAY == 1)
	{
		if($this_weekday == 0)
			$beginOfWeek = Date_Calc::dateToDays($day,$month,$year) - 6;
		else
			$beginOfWeek = Date_Calc::dateToDays($day,$month,$year)
				- $this_weekday + 1;
	}
	else
        	$beginOfWeek = (Date_Calc::dateToDays($day,$month,$year)
            	- $this_weekday);


       /*  $beginOfWeek = (Date_Calc::dateToDays($day,$month,$year)
            - ($this_weekday - DATE_CALC_BEGIN_WEEKDAY)); */

        return(Date_Calc::daysToDate($beginOfWeek,$format));

    } // end of func beginOfWeek

    /**
     * Find the month day of the end of week for given date,
     * using DATE_CALC_BEGIN_WEEKDAY. (can return weekday
     * of following month.)
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function endOfWeek($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $this_weekday = Date_Calc::dayOfWeek($day,$month,$year);

        $last_dayOfWeek = (Date_Calc::dateToDays($day,$month,$year)
            + (6 - $this_weekday + DATE_CALC_BEGIN_WEEKDAY));

        return(Date_Calc::daysToDate($last_dayOfWeek,$format));

    } // end func endOfWeek

    /**
     * Find the month day of the beginning of week after given date,
     * using DATE_CALC_BEGIN_WEEKDAY. (can return weekday of prev month.)
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function beginOfNextWeek($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $date = Date_Calc::daysToDate(Date_Calc::dateToDays($day+7,$month,$year),"%Y%m%d");

        $next_week_year = substr($date,0,4);
        $next_week_month = substr($date,4,2);
        $next_week_day = substr($date,6,2);

        $this_weekday = Date_Calc::dayOfWeek($next_week_day,$next_week_month,$next_week_year);

        $beginOfWeek = (Date_Calc::dateToDays($next_week_day,$next_week_month,$next_week_year)
            - ($this_weekday - DATE_CALC_BEGIN_WEEKDAY));

        return(Date_Calc::daysToDate($beginOfWeek,$format));

    } // end func beginOfNextWeek

    /**
     * Find the month day of the beginning of week before given date,
     * using DATE_CALC_BEGIN_WEEKDAY. (can return weekday of prev month.)
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function beginOfPrevWeek($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $date = Date_Calc::daysToDate(Date_Calc::dateToDays($day-7,$month,$year),"%Y%m%d");

        $next_week_year = substr($date,0,4);
        $next_week_month = substr($date,4,2);
        $next_week_day = substr($date,6,2);

        $this_weekday = Date_Calc::dayOfWeek($next_week_day,$next_week_month,$next_week_year);

        $beginOfWeek = (Date_Calc::dateToDays($next_week_day,$next_week_month,$next_week_year)
            - ($this_weekday - DATE_CALC_BEGIN_WEEKDAY));

        return(Date_Calc::daysToDate($beginOfWeek,$format));

    } // end func beginOfPrevWeek

    /**
     * Return an array with days in week
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param string format for returned date
     *
     * @access public
     *
     * @return array $week[$weekday]
     */

    static function getCalendarWeek($day="",$month="",$year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $week_array = array();

        // date for the column of week

        $curr_day = Date_Calc::beginOfWeek($day,$month,$year,"%E");

            for($counter=0; $counter <= 6; $counter++)
            {
                $week_array[$counter] = Date_Calc::daysToDate($curr_day,$format);
                $curr_day++;
            }

        return $week_array;

    } // end func getCalendarWeek

    /**
     * Return a set of arrays to construct a calendar month for
     * the given date.
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string format for returned date
     *
     * @access public
     *
     * @return array $month[$row][$col]
     */

    static function getCalendarMonth($month="",$year="",$format="%Y%m%d")
    {
        if(empty($year)) $year = Date_Calc::dateNow("%Y");
        if(empty($month)) $month = Date_Calc::dateNow("%m");
		$month_array = array();
		// starts on monday
		if(DATE_CALC_BEGIN_WEEKDAY == 1) {
			if(Date_Calc::firstOfMonthWeekday($month,$year) == 0) {
				$curr_day = Date_Calc::dateToDays("01",$month,$year) - 6;
			} else {
				$curr_day = Date_Calc::dateToDays("01",$month,$year) - Date_Calc::firstOfMonthWeekday($month,$year) + 1;
			}
		// starts on saturday
		} elseif(DATE_CALC_BEGIN_WEEKDAY == 6) {
			if(Date_Calc::firstOfMonthWeekday($month,$year) == 0) {
				$curr_day = Date_Calc::dateToDays("01",$month,$year) - 1;
			} else {
				$curr_day = Date_Calc::dateToDays("01",$month,$year) - Date_Calc::firstOfMonthWeekday($month,$year) - 1;
			}
		// starts on sunday		
		} else {
			$curr_day = (Date_Calc::dateToDays("01",$month,$year) - Date_Calc::firstOfMonthWeekday($month,$year));
		}		
		// number of days in this month
        $daysInMonth = Date_Calc::daysInMonth($month,$year);

        $weeksInMonth = Date_Calc::weeksInMonth($month,$year);
        for($row_counter=0; $row_counter < $weeksInMonth; $row_counter++)
        {
            for($column_counter=0; $column_counter <= 6; $column_counter++)
            {
                $month_array[$row_counter][$column_counter] = Date_Calc::daysToDate($curr_day,$format);
                $curr_day++;
            }
        }

        return $month_array;

    } // end func getCalendarMonth

    /**
     * Return a set of arrays to construct a calendar year for
     * the given date.
     *
     * @param string year in format CCYY, default current local year
     * @param string format for returned date
     *
     * @access public
     *
     * @return array $year[$month][$row][$col]
     */

    static function getCalendarYear($year="",$format="%Y%m%d")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");

        $year_array = array();

        for($curr_month=0; $curr_month <=11; $curr_month++)
            $year_array[$curr_month] = Date_Calc::getCalendarMonth(sprintf("%02d",$curr_month+1),$year,$format);

        return $year_array;

    } // end func getCalendarYear

    /**
     * Converts a date to number of days since a
     * distant unspecified epoch.
     *
     * @param string year in format CCYY
     * @param string month in format MM
     * @param string day in format DD
     *
     * @access public
     *
     * @return integer number of days
     */

    static function dateToDays($day,$month,$year)
    {

        $century = substr($year,0,2);
        $year = substr($year,2,2);

        if($month > 2)
            $month -= 3;
        else
        {
            $month += 9;
            if($year)
                $year--;
            else
            {
                $year = 99;
                $century --;
            }
        }

        return ( floor((  146097 * $century)    /  4 ) +
                floor(( 1461 * $year)        /  4 ) +
                floor(( 153 * $month +  2) /  5 ) +
                    $day +  1721119);

    } // end func dateToDays

    /**
     * Converts number of days to a distant unspecified epoch.
     *
     * @param int number of days
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in specified format
     */

    static function daysToDate($days,$format="%Y%m%d")
    {

        $days         -=     1721119;
        $century     =    floor(( 4 * $days -  1) /  146097);
        $days        =    floor(4 * $days - 1 - 146097 * $century);
        $day        =    floor($days /  4);

        $year        =    floor(( 4 * $day +  3) /  1461);
        $day        =    floor(4 * $day +  3 -  1461 * $year);
        $day        =    floor(($day +  4) /  4);

        $month        =    floor(( 5 * $day -  3) /  153);
        $day        =    floor(5 * $day -  3 -  153 * $month);
        $day        =    floor(($day +  5) /  5);

        if($month < 10)
            $month +=3;
        else
        {
            $month -=9;
            if($year++ == 99)
            {
                $year = 0;
                $century++;
            }
        }

        $century = sprintf("%02d",$century);
        $year = sprintf("%02d",$year);

        return(Date_Calc::dateFormat($day,$month,$century.$year,$format));

    } // end func daysToDate

    /**
     * Calculates the date of the Nth weekday of the month,
     * such as the second Saturday of January 2000.
     *
     * @param string occurance: 1=first, 2=second, 3=third, etc.
     * @param string dayOfWeek: 0=Sunday, 1=Monday, etc.
     * @param string year in format CCYY
     * @param string month in format MM
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function NWeekdayOfMonth($occurance,$dayOfWeek,$month,$year,$format="%Y%m%d")    {

        $year = sprintf("%04d",$year);
        $month = sprintf("%02d",$month);

        $DOW1day = sprintf("%02d",(($occurance - 1) * 7 + 1));
        $DOW1 = Date_Calc::dayOfWeek($DOW1day,$month,$year);

        $wdate = ($occurance - 1) * 7 + 1 +
                (7 + $dayOfWeek - $DOW1) % 7;

        if( $wdate > Date_Calc::daysInMonth($month,$year))
                return -1;
        else
                return(Date_Calc::dateFormat($wdate,$month,$year,$format));

    } // end func NWeekdayOfMonth

    /**
     *  Formats the date in the given format, much like
     *  strfmt(). This function is used to alleviate the
     *  problem with 32-bit numbers for dates pre 1970
     *  or post 2038, as strfmt() has on most systems.
     *  Most of the formatting options are compatible.
     *
     *  formatting options:
     *
     *  %a        abbreviated weekday name (Sun, Mon, Tue)
     *  %A        full weekday name (Sunday, Monday, Tuesday)
     *  %b        abbreviated month name (Jan, Feb, Mar)
     *  %B        full month name (January, February, March)
     *  %d        day of month (range 00 to 31)
     *  %e        day of month, single digit (range 0 to 31)
     *  %E        number of days since unspecified epoch (integer)
     *             (%E is useful for passing a date in a URL as
     *             an integer value. Then simply use
     *             daysToDate() to convert back to a date.)
     *  %j        day of year (range 001 to 366)
     *  %m        month as decimal number (range 1 to 12)
     *  %n        newline character (\n)
     *  %t        tab character (\t)
     *  %w        weekday as decimal (0 = Sunday)
     *  %U        week number of current year, first sunday as first week
     *  %y        year as decimal (range 00 to 99)
     *  %Y        year as decimal including century (range 0000 to 9999)
     *  %%        literal '%'
     *
     * @param string year in format CCYY
     * @param string month in format MM
     * @param string day in format DD
     * @param string format for returned date
     *
     * @access public
     *
     * @return string date in given format
     */

    static function dateFormat($day,$month,$year,$format)
    {
        if(!Date_Calc::isValidDate($day,$month,$year))
        {
            $year = Date_Calc::dateNow("%Y");
            $month = Date_Calc::dateNow("%m");
            $day = Date_Calc::dateNow("%d");
        }

        $output = "";

        for($strpos = 0; $strpos < strlen($format); $strpos++)
        {
            $char = substr($format,$strpos,1);
            if($char == "%")
            {
                $nextchar = substr($format,$strpos + 1,1);
                switch($nextchar)
                {
                    case "a":
                        $output .= Date_Calc::getWeekdayAbbrname($day,$month,$year);
                        break;
                    case "A":
                        $output .= Date_Calc::getWeekdayFullname($day,$month,$year);
                        break;
                    case "b":
                        $output .= Date_Calc::getMonthAbbrname($month);
                        break;
                    case "B":
                        $output .= Date_Calc::getMonthFullname($month);
                        break;
                    case "d":
                        $output .= sprintf("%02d",$day);
                        break;
                    case "e":
                        $output .= $day;
                        break;
                    case "E":
                        $output .= Date_Calc::dateToDays($day,$month,$year);
                        break;
                    case "j":
                        $output .= Date_Calc::julianDate($day,$month,$year);
                        break;
                    case "m":
                        $output .= sprintf("%02d",$month);
                        break;
                    case "n":
                        $output .= "\n";
                        break;
                    case "t":
                        $output .= "\t";
                        break;
                    case "w":
                        $output .= Date_Calc::dayOfWeek($day,$month,$year);
                        break;
                    case "U":
                        $output .= Date_Calc::weekOfYear($day,$month,$year);
                        break;
                    case "y":
                        $output .= substr($year,2,2);
                        break;
                    case "Y":
                        $output .= $year;
                        break;
                    case "%":
                        $output .= "%";
                        break;
                    default:
                        $output .= $char.$nextchar;
                }
                $strpos++;
            }
            else
            {
                $output .= $char;
            }
        }
        return $output;

    } // end func dateFormat

    /**
     * Returns the current local year in format CCYY
     *
     * @access public
     *
     * @return string year in format CCYY
     */

    static function getYear()
    {
        return Date_Calc::dateNow("%Y");

    } // end func getYear

    /**
     * Returns the current local month in format MM
     *
     * @access public
     *
     * @return string month in format MM
     */

    static function getMonth()
    {
        return Date_Calc::dateNow("%m");

    } // end func getMonth

    /**
     * Returns the current local day in format DD
     *
     * @access public
     *
     * @return string day in format DD
     */

    static function getDay()
    {
        return Date_Calc::dateNow("%d");

    } // end func getDay

    /**
     * Returns the full month name for the given month
     *
     * @param string month in format MM
     *
     * @access public
     *
     * @return string full month name
     */

    static function getMonthFullname($month)
    {
        $month = (int)$month;

        if(empty($month))
            $month = Date_Calc::dateNow("%m");

        $month_names = Date_Calc::getMonthNames();
        return $month_names[$month];
        // getMonthNames returns months with correct indexes
        //return $month_names[($month - 1)];

    } // end func getMonthFullname

    /**
     * Returns the abbreviated month name for the given month
     *
     * @param string month in format MM
     * @param int optional length of abbreviation, default is 3
     *
     * @access public
     *
     * @return string abbreviated month name
     * @see Date_Calc::getMonthFullname
     */

    static function getMonthAbbrname($month,$length=3)
    {
        $month = (int)$month;

        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        return substr(Date_Calc::getMonthFullname($month), 0, $length);
    } // end func getMonthAbbrname

    /**
     * Returns the full weekday name for the given date
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     *
     * @access public
     *
     * @return string full month name
     */

    static function getWeekdayFullname($day="",$month="",$year="")
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");

        $weekday_names = Date_Calc::getWeekDays();
        $weekday = Date_Calc::dayOfWeek($day,$month,$year);

        return $weekday_names[$weekday];

    } // end func getWeekdayFullname

    /**
     * Returns the abbreviated weekday name for the given date
     *
     * @param string year in format CCYY, default current local year
     * @param string month in format MM, default current local month
     * @param string day in format DD, default current local day
     * @param int optional length of abbreviation, default is 3
     *
     * @access public
     *
     * @return string full month name
     * @see Date_Calc::getWeekdayFullname
     */

    static function getWeekdayAbbrname($day="",$month="",$year="",$length=3)
    {
        if(empty($year))
            $year = Date_Calc::dateNow("%Y");
        if(empty($month))
            $month = Date_Calc::dateNow("%m");
        if(empty($day))
            $day = Date_Calc::dateNow("%d");
        return substr(Date_Calc::getWeekdayFullname($day,$month,$year),0,$length);
    } // end func getWeekdayFullname

    /**
    * Returns the numeric month from the month name or an abreviation
    *
    * Both August and Aug would return 8.
    * Month name is case insensitive.
    *
    * @param    string  month name
    * @return   integer month number
    */
    static function getMonthFromFullName($month){
        $month = strtolower($month);
        $months = Date_Calc::getMonthNames();
        while(list($id, $name) = each($months)){
            if(preg_match("/" . addcslashes($month, '/') . "/", strtolower($name))){
                return($id);
            }
        }
        return(0);
    }

    /**
    * Retunrs an array of month names
    *
    * Used to take advantage of the setlocale function to return
    * language specific month names.
    * XXX cache values to some global array to avoid preformace hits when called more than once.
    *
    * @returns array An array of month names
    */
    static function getMonthNames(){
        for($i=1;$i<13;$i++){
            $months[$i] = strftime('%B', mktime(0, 0, 0, $i, 1, 2001));
        }
        return($months);
    }

    /**
    * Returns an array of week days
    *
    * Used to take advantage of the setlocale function to
    * return language specific week days
    * XXX cache values to some global array to avoid preformace hits when called more than once.
    *
    * @returns array An array of week day names
    */
    static function getWeekDays(){
        for($i=0;$i<7;$i++){
            $weekdays[$i] = strftime('%A', mktime(0, 0, 0, 1, $i, 2001));
        }
        return($weekdays);
    }

} // end class Date_calendar

?>