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<?php
namespace Fisharebest\ExtCalendar;
/**
* class JulianCalendar - calculations for the Julian calendar.
*
* @author Greg Roach <fisharebest@gmail.com>
* @copyright (c) 2014 Greg Roach
* @license This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* 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, see <http://www.gnu.org/licenses/>.
*/
class JulianCalendar extends Calendar implements CalendarInterface {
/** Same as PHP’s ext/calendar extension */
const PHP_CALENDAR_NAME = 'Julian';
/** Same as PHP’s ext/calendar extension */
const PHP_CALENDAR_NUMBER = 1;
/** Same as PHP’s ext/calendar extension */
const PHP_CALENDAR_SYMBOL = 'CAL_JULIAN';
/** See the GEDCOM specification */
const GEDCOM_CALENDAR_ESCAPE = '@#DJULIAN@';
/**
* Month lengths for regular years and leap-years.
*
* @var int[][]
*/
protected static $DAYS_IN_MONTH = array(
0 => array(1 => 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31),
1 => array(1 => 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31),
);
/**
* English month names.
*
* @return string[]
*/
public function monthNames() {
return array(
1 => 'January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December',
);
}
/**
* Abbreviated English month names.
*
* @return string[]
*/
public function monthNamesAbbreviated() {
return array(
1 => 'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec',
);
}
/**
* Determine whether a year is a leap year.
*
* @param int $year
* @return bool
*/
public function leapYear($year) {
if ($year < 0) {
$year++;
}
return $year % 4 == 0;
}
/**
* Convert a Julian day number into a year/month/day.
*
* @param $jd
*
* @return int[];
*/
public function jdToYmd($jd) {
$c = $jd + 32082;
$d = (int)((4 * $c + 3) / 1461);
$e = $c - (int)(1461 * $d / 4);
$m = (int)((5 * $e + 2) / 153);
$day = $e - (int)((153 * $m + 2) / 5) + 1;
$month = $m + 3 - 12 * (int)($m / 10);
$year = $d - 4800 + (int)($m / 10);
if ($year < 1) {
// 0=1BC, -1=2BC, etc.
$year--;
}
return array($year, $month, $day);
}
/**
* Convert a year/month/day into a Julian day number
*
* @param int $year
* @param int $month
* @param int $day
*
* @return int
*/
public function ymdToJd($year, $month, $day) {
if ($year < 0) {
// 1 B.C.E. => 0, 2 B.C.E> => 1, etc.
++$year;
}
$a = (int)((14 - $month) / 12);
$year = $year + 4800 - $a;
$month = $month + 12 * $a - 3;
return $day + (int)((153 * $month + 2) / 5) + 365 * $year + (int)($year / 4) - 32083;
}
/**
* Calculate the number of days in a month.
*
* @param int $year
* @param int $month
*
* @return int
*/
public function daysInMonth($year, $month) {
if ($year == 0 || $month < 1 || $month > 12) {
return trigger_error('invalid date.', E_USER_WARNING);
} else {
return static::$DAYS_IN_MONTH[$this->leapYear($year)][$month];
}
}
/**
* Get the number of days after March 21 that easter falls, for a given year.
*
* Uses the algorithm found in PHP’s ext/calendar/easter.c
*
* @param int $year
*
* @return int
*/
public function easterDays($year) {
// The “golden” number
$golden = 1 + $year % 19;
// The “dominical” number (finding a Sunday)
$dom = ($year + (int)($year / 4) + 5) % 7;
if ($dom < 0) {
$dom += 7;
}
// The uncorrected “Paschal full moon” date
$pfm = (3 - 11 * $golden - 7) % 30;
if ($pfm < 0) {
$pfm += 30;
}
// The corrected “Paschal full moon” date
if ($pfm == 29 || $pfm == 28 && $golden > 11) {
$pfm--;
}
$tmp = (4 - $pfm - $dom) % 7;
if ($tmp < 0) {
$tmp += 7;
}
return $pfm + $tmp + 1;
}
}
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