<?php
/**
 * Notification retry / backoff policy.
 *
 * @package Bookline
 */

declare( strict_types=1 );

namespace Bookline\Domain\Notification;

use DateInterval;
use DateTimeImmutable;

/**
 * Exponential backoff: 1m, 5m, 30m, 2h, 12h — max five attempts.
 *
 * @since 0.1.0
 */
final class RetryPolicy {

	public const MAX_ATTEMPTS = 5;

	/**
	 * Backoff delays in seconds indexed by attempt number (1-based after failure).
	 */
	private const DELAYS = [ 60, 300, 1800, 7200, 43200 ];

	/**
	 * Whether another attempt is allowed after the given attempt count.
	 *
	 * @param int $attempts Attempts already made.
	 *
	 * @since 0.1.0
	 */
	public function can_retry( int $attempts ): bool {
		return $attempts < self::MAX_ATTEMPTS;
	}

	/**
	 * Seconds to wait before the next attempt after `$attempts` failures.
	 *
	 * @param int $attempts Attempts so far (1 after first failure).
	 *
	 * @since 0.1.0
	 */
	public function delay_seconds( int $attempts ): int {
		$index = max( 0, min( $attempts - 1, count( self::DELAYS ) - 1 ) );
		return self::DELAYS[ $index ];
	}

	/**
	 * Next run instant.
	 *
	 * @param DateTimeImmutable $now      Now.
	 * @param int               $attempts Attempts so far.
	 *
	 * @since 0.1.0
	 */
	public function next_attempt_at( DateTimeImmutable $now, int $attempts ): DateTimeImmutable {
		return $now->add( new DateInterval( 'PT' . $this->delay_seconds( $attempts ) . 'S' ) );
	}
}