<?php
namespace Advently\Calendar;

defined( 'ABSPATH' ) || exit;

/**
 * The order doors are laid out in: 1, 2, 3… or shuffled like a real advent
 * calendar. The shuffle is seeded by the start date, so the same calendar
 * always looks the same; assets/src/admin/layout.js mirrors it exactly.
 */
final class Layout {

	/**
	 * @return int[] Door numbers in grid order.
	 */
	public static function order( int $doors, string $start, bool $shuffle ): array {
		$order = range( 1, max( 1, $doors ) );
		if ( ! $shuffle ) {
			return $order;
		}
		// Park–Miller: small integers only, identical results in PHP and JavaScript.
		$x = ( (int) preg_replace( '/\D/', '', $start ) % 2147483646 ) + 1;
		// The first steps stay close to the seed; skip them.
		for ( $k = 0; $k < 8; $k++ ) {
			$x = ( $x * 48271 ) % 2147483647;
		}
		for ( $i = count( $order ) - 1; $i > 0; $i-- ) {
			$x           = ( $x * 48271 ) % 2147483647;
			$j           = $x % ( $i + 1 );
			$tmp         = $order[ $i ];
			$order[ $i ] = $order[ $j ];
			$order[ $j ] = $tmp;
		}
		return $order;
	}
}