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<?php
/* vim: set expandtab tabstop=4 shiftwidth=4: */
// +----------------------------------------------------------------------+
// | PHP Version 4                                                        |
// +----------------------------------------------------------------------+
// | Copyright (c) 1997-2002 The PHP Group                                |
// +----------------------------------------------------------------------+
// | This source file is subject to version 2.0 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.               |
// +----------------------------------------------------------------------+
// | Authors: Ondrej Jombik <nepto@pobox.sk>                              |
// +----------------------------------------------------------------------+
//
// $Id: Week_Magic.php,v 1.1 2005/06/05 12:14:13 nepto Exp $

/**
 * Date_Week_Magic - ISO 8601 implemetation
 *
 * This package implements ISO 8601 specification. It can count week and day
 * number for specified date. It can also count date of Monday for
 * specified week in year.
 *
 * Usage:
 * <?php
 *         require_once 'Date/Week_Magic.php';
 * 
 *         // First example
 *         $day   = 1;
 *         $month = 6;
 *         $year  = 1981;
 *         $ar    = Date_Week_Magic::week($year, $month, $day);
 * 
 *         echo "Date $day/$month/$year was day $ar[weekday] in week $ar[week].";
 * 
 *         // Second example
 *         $week = 50;
 *         $year = 1998;
 *         $ar   = Date_Week_Magic::monday($year, $week);
 * 
 *         echo "Monday of week $week in year $year was $ar[day]/$ar[month].";
 * ?>
 *
 * @author  Ondrej Jombik <nepto@pobox.sk>
 * @package Date_Week_Magic
 * @version 0.1
 * @access  public
 */
class Date_Week_Magic
{
    /**
     * Validate date
     *
     * Validate passed date.
     *
     * @access    public
     * @param    int $year    year (allowed forms: YYYY, YY)
     * @param    int $month    month (from 1 to 12)
     * @param    int $day    day (from 1 to 31)
     * @return    bool        true if is valid date, false otherwise
     */
    function validate($year, $month, $day)
    {
        $timeNowInSeconds = mktime(0, 0, 0, $month, $day, $year);
        $timeNow = localtime($timeNowInSeconds, 1 /* associative */);

        if ((($timeNow['tm_year'] >= 100 && $timeNow['tm_year'] - 100 == $year)
                    || ($timeNow['tm_year'] < 100 && $timeNow['tm_year'] == $year)
                    || (1900 + $timeNow['tm_year'] == $year))
                && $timeNow['tm_mon'] + 1 == $month
                && $timeNow['tm_mday'] == $day)
        {
            return true;
        }

        return false;
    }

    /**
     * Get week information for date
     *
     * Method returns associative array with two keys: week and weekday.
     * Key week contain week number (from 1 to 53) and weekday contain week
     * day number.  First day of week is Monday with value of 1. Sunday
     * have value 7. 0 is undefined. On error, false is returned.
     *
     * @access    public
     * @param    int $year    year (allowed forms: YYYY, YY)
     * @param    int $month    month (from 1 to 12)
     * @param    int $day    day (from 1 to 31)
     * @return    array        'week' => week number
     *                         'weekday' => week day (1 - Mon, 7 - Sun)
     *                        on error false is returned
     */
    function week($year, $month, $day)
    {
        if (Date_Week_Magic::validate($year, $month, $day) == false) {
            return false;
        }

        $timeNow = localtime(mktime(0, 0, 0, $month, $day, $year),
                1 /* associative */);

        // Function localtime() 'tm_yday' 0 based, we need it 1 based.
        $YearDay_I = $timeNow['tm_yday'] + 1;
        $yearNow   = $timeNow['tm_year'];

        // American weeks begin on Sundays. ISO doesn't.
        $WeekDay_I = $timeNow['tm_wday'];
        if (0 == $WeekDay_I) {        // if it's Sunday
            $WeekDay_I = 7;            // make it Sunday
        }

        $WeekNo_I    = intval($YearDay_I / 7);
        $FirstWeek_I = $YearDay_I % 7;

        $FirstWeek_I -= $WeekDay_I;
        if (($FirstWeek_I <= 0) && ($WeekNo_I > 0)) {
            // Break up one week and add the days to FirstWeek_I.
            $WeekNo_I--;
            $FirstWeek_I += 7;
        }

        if ($FirstWeek_I > (-4)) {
            $WeekNo_I += 1;
        }

        if ($FirstWeek_I > 3) {
            $WeekNo_I += 1;
        }

        if ($WeekNo_I == 0) {
            // Same as previous year's last day.

            $ar = Date_Week_Magic::week($year - 1, 12 /* December is 12 */, 31);
            $WeekNo_I = $ar['week'];
        }
        else if($WeekNo_I > 52) {
            // The last days of the year.
            if($WeekDay_I < 4 && $day > 28) {
                // Three or less days of this year in 53 makes it week 1 instead!
                $WeekNo_I = 1;
            }
        }

        return array(
                'week'    => $WeekNo_I,
                'weekday' => $WeekDay_I
                );
    }

    /**
     * Get day information for week
     *
     * Returns asssociative array with two keys: day and month. It is day and
     * month of Monday of passed week and year. Note, that the first week can
     * begin in the previous year.
     *
     * @access    public
     * @param    int $year    year (allowed forms: YYYY, YY)
     * @param    int $week    week (from 1 to 53)
     * @return    array        'day' => day of Monday
     *                         'month' => month of Monday
     *                        on error false is returned
     */
    function monday($year, $week)
    {
        $day = 15;

        while ($week > 53) {
            $week -= 53;
        }

        $month = intval((11 * $week) / 53); // assume 53 weeks a year

        while (1) {
            $ar = Date_Week_Magic::week($year, $month + 1, $day);
            if ($ar == false) {
                $month++;
                $day = 1;
                continue;
            }

            $getweek = $ar['week'];
            $getday  = $ar['weekday'];

            if (($getweek > $week - 3) && ($getweek < $week + 3)) {
                if (($getweek == $week) && ($getday == 1)) {
                    break;
                }
                else {
                    if ($day == 1 && $month == 0) {
                        return false;
                    }

                    if ($getweek < $week) {
                        if ($week - $getweek > 1) {
                            $day += 7;
                        }
                        else {
                            $day += (8 - $getday);
                        }
                    }
                    else {
                        if ($getweek - $week > 1) {
                            $day -= 7;
                        }
                        else if ($getweek == $week) {
                            $day -= ($getday - 1);
                        }
                        else {
                            $day -= ($getday + 6);
                        }

                        if ($day <= 0) {
                            $day = 28;
                            $month--;
                        }
                    }
                }
            }
            else {
                if(++$month > 11) {
                    return false;
                }
            }
        }

        return array(
                'day'   => $day,
                'month' => $month + 1
                );
    }

}

?>