<?php
namespace Fisharebest\ExtCalendar;

use InvalidArgumentException;

/**
 * Class PersianCalendar - calculations for the Persian (Jalali) calendar.
 *
 * Algorithms for Julian days based on https://www.fourmilab.ch/documents/calendar/
 *
 * @author    Greg Roach <fisharebest@gmail.com>
 * @copyright (c) 2014-2017 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 PersianCalendar implements CalendarInterface
{
    /**
     * In each 128 year cycle, the following years are leap years.
     *
     * @var int[]
     */
    private static $LEAP_YEAR_CYCLE = array(
        0, 5, 9, 13, 17, 21, 25, 29, 34, 38, 42, 46, 50, 54, 58, 62, 67, 71, 75, 79, 83, 87, 91, 95, 100, 104, 108, 112, 116, 120, 124
    );

    /**
     * Determine the number of days in a specified month, allowing for leap years, etc.
     *
     * @param int $year
     * @param int $month
     *
     * @return int
     */
    public function daysInMonth($year, $month)
    {
        if ($month <= 6) {
            return 31;
        } elseif ($month <= 11 || $this->isLeapYear($year)) {
            return 30;
        } else {
            return 29;
        }
    }

    /**
     * Determine the number of days in a week.
     *
     * @return int
     */
    public function daysInWeek()
    {
        return 7;
    }

    /**
     * The escape sequence used to indicate this calendar in GEDCOM files.
     *
     * @return string
     */
    public function gedcomCalendarEscape()
    {
        return '@#DJALALI@';
    }

    /**
     * Determine whether or not a given year is a leap-year.
     *
     * @param int $year
     *
     * @return bool
     */
    public function isLeapYear($year)
    {
        return in_array((($year + 2346) % 2820) % 128, self::$LEAP_YEAR_CYCLE);
    }

    /**
     * What is the highest Julian day number that can be converted into this calendar.
     *
     * @return int
     */
    public function jdEnd()
    {
        return PHP_INT_MAX;
    }

    /**
     * What is the lowest Julian day number that can be converted into this calendar.
     *
     * @return int
     */
    public function jdStart()
    {
        return 1948321; // 1 Farvardīn 0001 AP, 19 MAR 0622 AD
    }

    /**
     * Convert a Julian day number into a year/month/day.
     *
     * @param int $julian_day
     *
     * @return int[]
     */
    public function jdToYmd($julian_day)
    {
        $depoch = $julian_day - 2121446; // 1 Farvardīn 475
        $cycle  = (int) floor($depoch / 1029983);
        $cyear  = $this->mod($depoch, 1029983);
        if ($cyear == 1029982) {
            $ycycle = 2820;
        } else {
            $aux1   = (int) ($cyear / 366);
            $aux2   = $cyear % 366;
            $ycycle = (int) (((2134 * $aux1) + (2816 * $aux2) + 2815) / 1028522) + $aux1 + 1;
        }
        $year = $ycycle + (2820 * $cycle) + 474;

        // If we allowed negative years, we would deal with them here.
        $yday  = $julian_day - $this->ymdToJd($year, 1, 1) + 1;
        $month = ($yday <= 186) ? ceil($yday / 31) : ceil(($yday - 6) / 30);
        $day   = $julian_day - $this->ymdToJd($year, $month, 1) + 1;

        return array((int) $year, (int) $month, (int) $day);
    }

    /**
     * Determine the number of months in a year (if given),
     * or the maximum number of months in any year.
     *
     * @param int|null $year
     *
     * @return int
     */
    public function monthsInYear($year = null)
    {
        return 12;
    }

    /**
     * Convert a year/month/day to a Julian day number.
     *
     * @param int $year
     * @param int $month
     * @param int $day
     *
     * @return int
     */
    public function ymdToJd($year, $month, $day)
    {
        if ($month < 1 || $month > $this->monthsInYear()) {
            throw new InvalidArgumentException('Month ' . $month . ' is invalid for this calendar');
        }

        $epbase = $year - (($year >= 0) ? 474 : 473);
        $epyear = 474 + $this->mod($epbase, 2820);

        return
            $day +
            (($month <= 7) ? (($month - 1) * 31) : ((($month - 1) * 30) + 6)) +
            (int) ((($epyear * 682) - 110) / 2816) +
            ($epyear - 1) * 365 +
            (int) (floor($epbase / 2820)) * 1029983 +
            $this->jdStart() - 1;
    }

    /**
     * The PHP modulus function returns a negative modulus for a negative dividend.
     * This algorithm requires a "traditional" modulus function where the modulus is
     * always positive.
     *
     * @param int $dividend
     * @param int $divisor
     *
     * @return int
     */
    public function mod($dividend, $divisor)
    {
        if ($divisor === 0) {
            return 0;
        }

        $modulus = $dividend % $divisor;
        if ($modulus < 0) {
            $modulus += $divisor;
        }

        return $modulus;
    }
}
