<?php
/**
 * Umm al-Qura Hijri calendar: a PHP port of adawat.org's public/assets/hijri.js.
 *
 * The browser library delegates to Intl's `islamic-umalqura` calendar (ICU).
 * This class reproduces the same calendar from a month-length table generated
 * out of that exact ICU data (includes/umalqura-data.php), so PHP and the live
 * site agree day-for-day for Hijri years 1300-1600 AH (1882-2174 CE).
 *
 * No WordPress dependency: the class is plain PHP so it can be unit-tested
 * from the command line (see wp-plugin/scripts/test-hijri-php.php).
 *
 * @package Adawat_Tools
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Hijri (Umm al-Qura) date conversion.
 */
class Adawat_Tools_Hijri {

	/**
	 * Arabic Hijri month names, same order/spelling as hijri.js MONTHS.
	 *
	 * @var string[]
	 */
	public static $months = array(
		'محرم',
		'صفر',
		'ربيع الأول',
		'ربيع الآخر',
		'جمادى الأولى',
		'جمادى الآخرة',
		'رجب',
		'شعبان',
		'رمضان',
		'شوال',
		'ذو القعدة',
		'ذو الحجة',
	);

	/**
	 * Arabic weekday names (Sunday first), same as hijri.js DAYS.
	 *
	 * @var string[]
	 */
	public static $days = array( 'الأحد', 'الاثنين', 'الثلاثاء', 'الأربعاء', 'الخميس', 'الجمعة', 'السبت' );

	/**
	 * Table data from umalqura-data.php.
	 *
	 * @var array|null
	 */
	private static $data = null;

	/**
	 * Epoch-day (days since 1970-01-01) of the start of each table month.
	 *
	 * @var int[]|null
	 */
	private static $month_starts = null;

	/**
	 * Loads the generated table and builds the cumulative month-start index.
	 *
	 * @return array{0:array,1:int[]} Data array and month-start days.
	 */
	private static function table() {
		if ( null === self::$month_starts ) {
			self::$data = include __DIR__ . '/umalqura-data.php';
			$starts     = array();
			$day        = self::$data['start_day'];
			foreach ( self::$data['months'] as $bits ) {
				for ( $m = 0; $m < 12; $m++ ) {
					$starts[] = $day;
					$day     += ( $bits >> $m ) & 1 ? 30 : 29;
				}
			}
			$starts[]           = $day; // == end_day, used as the exclusive upper bound.
			self::$month_starts = $starts;
		}
		return array( self::$data, self::$month_starts );
	}

	/**
	 * Days since 1970-01-01 for a proleptic-Gregorian Y-M-D (no DST/timezone).
	 *
	 * Same day arithmetic as hijri.js utc(): Date.UTC(y, m-1, d) / 86400000.
	 *
	 * @param int $y Gregorian year.
	 * @param int $m Gregorian month 1-12.
	 * @param int $d Gregorian day 1-31.
	 * @return int Epoch day.
	 */
	public static function epoch_day( $y, $m, $d ) {
		// Days from civil date, Howard Hinnant's algorithm (valid for all ints).
		$y -= $m <= 2 ? 1 : 0;
		$era = intdiv( $y >= 0 ? $y : $y - 399, 400 );
		$yoe = $y - $era * 400;                                  // [0, 399]
		$doy = intdiv( 153 * ( $m + ( $m > 2 ? -3 : 9 ) ) + 2, 5 ) + $d - 1; // [0, 365]
		$doe = $yoe * 365 + intdiv( $yoe, 4 ) - intdiv( $yoe, 100 ) + $doy;  // [0, 146096]
		return $era * 146097 + $doe - 719468;
	}

	/**
	 * Proleptic-Gregorian Y-M-D from days since 1970-01-01.
	 *
	 * @param int $day Epoch day.
	 * @return array{y:int,m:int,d:int}
	 */
	public static function from_epoch_day( $day ) {
		$day += 719468;
		$era  = intdiv( $day >= 0 ? $day : $day - 146096, 146097 );
		$doe  = $day - $era * 146097;                            // [0, 146096]
		$yoe  = intdiv( $doe - intdiv( $doe, 1460 ) + intdiv( $doe, 36524 ) - intdiv( $doe, 146096 ), 365 );
		$y    = $yoe + $era * 400;
		$doy  = $doe - ( 365 * $yoe + intdiv( $yoe, 4 ) - intdiv( $yoe, 100 ) );
		$mp   = intdiv( 5 * $doy + 2, 153 );
		$d    = $doy - intdiv( 153 * $mp + 2, 5 ) + 1;
		$m    = $mp + ( $mp < 10 ? 3 : -9 );
		return array(
			'y' => $y + ( $m <= 2 ? 1 : 0 ),
			'm' => $m,
			'd' => $d,
		);
	}

	/**
	 * Gregorian -> Hijri (Umm al-Qura). Port of hijri.js toHijri().
	 *
	 * @param int $gy Gregorian year.
	 * @param int $gm Gregorian month 1-12.
	 * @param int $gd Gregorian day.
	 * @return array{y:int,m:int,d:int}|false Hijri date, or false outside 1300-1600 AH.
	 */
	public static function to_hijri( $gy, $gm, $gd ) {
		list( $data, $starts ) = self::table();
		$day                   = self::epoch_day( $gy, $gm, $gd );
		if ( $day < $data['start_day'] || $day >= $data['end_day'] ) {
			return false;
		}
		// Binary search: greatest i with starts[i] <= day.
		$lo = 0;
		$hi = count( $starts ) - 1;
		while ( $lo + 1 < $hi ) {
			$mid = intdiv( $lo + $hi, 2 );
			if ( $starts[ $mid ] <= $day ) {
				$lo = $mid;
			} else {
				$hi = $mid;
			}
		}
		return array(
			'y' => $data['start_year'] + intdiv( $lo, 12 ),
			'm' => ( $lo % 12 ) + 1,
			'd' => $day - $starts[ $lo ] + 1,
		);
	}

	/**
	 * Hijri (Umm al-Qura) -> Gregorian. Port of hijri.js toGregorian().
	 *
	 * @param int $hy Hijri year.
	 * @param int $hm Hijri month 1-12.
	 * @param int $hd Hijri day 1-30.
	 * @return array{y:int,m:int,d:int}|false Gregorian date, or false when the
	 *                                        date does not exist (e.g. day 30 of
	 *                                        a 29-day month) or is out of range.
	 */
	public static function to_gregorian( $hy, $hm, $hd ) {
		list( $data, $starts ) = self::table();
		if ( $hy < $data['start_year'] || $hy > $data['end_year'] || $hm < 1 || $hm > 12 || $hd < 1 ) {
			return false;
		}
		$i   = ( $hy - $data['start_year'] ) * 12 + ( $hm - 1 );
		$len = $starts[ $i + 1 ] - $starts[ $i ];
		if ( $hd > $len ) {
			return false; // تاريخ غير موجود (مثلاً يوم 30 بشهر 29 يوم) — same contract as hijri.js.
		}
		return self::from_epoch_day( $starts[ $i ] + $hd - 1 );
	}

	/**
	 * Number of days in a Hijri month.
	 *
	 * @param int $hy Hijri year.
	 * @param int $hm Hijri month 1-12.
	 * @return int|false 29 or 30, false out of range.
	 */
	public static function month_length( $hy, $hm ) {
		list( $data, $starts ) = self::table();
		if ( $hy < $data['start_year'] || $hy > $data['end_year'] || $hm < 1 || $hm > 12 ) {
			return false;
		}
		$i = ( $hy - $data['start_year'] ) * 12 + ( $hm - 1 );
		return $starts[ $i + 1 ] - $starts[ $i ];
	}

	/**
	 * Today's Hijri date in a given timezone. Port of Hijri.toHijri(Hijri.today()).
	 *
	 * @param DateTimeZone|null $tz  Timezone (site timezone in WP); UTC when null.
	 * @param int|null          $now Unix timestamp, defaults to now.
	 * @return array{y:int,m:int,d:int,wd:int}|false Hijri date plus weekday 0=Sunday.
	 */
	public static function today( $tz = null, $now = null ) {
		$ts = null === $now ? time() : (int) $now;
		$dt = new DateTime( '@' . $ts );
		if ( $tz instanceof DateTimeZone ) {
			$dt->setTimezone( $tz );
		}
		$h = self::to_hijri( (int) $dt->format( 'Y' ), (int) $dt->format( 'n' ), (int) $dt->format( 'j' ) );
		if ( false === $h ) {
			return false;
		}
		$h['wd'] = (int) $dt->format( 'w' ); // 0 = Sunday, matches self::$days.
		return $h;
	}

	/**
	 * "14 ربيع الآخر 1448 هـ" — port of hijri.js formatHijri().
	 *
	 * @param array $h Hijri array {y,m,d}.
	 * @return string
	 */
	public static function format_hijri( $h ) {
		return $h['d'] . ' ' . self::$months[ $h['m'] - 1 ] . ' ' . $h['y'] . ' هـ';
	}
}