<?php
/**
 * Deterministic clock for tests.
 *
 * @package Bookline
 */

declare( strict_types=1 );

namespace Bookline\Domain\Shared;

use DateTimeImmutable;
use DateTimeZone;

/**
 * Returns a fixed instant; advance() moves it forward without sleeping.
 *
 * @since 0.1.0
 */
final class FrozenClock implements Clock {

	/**
	 * Frozen instant (always stored as UTC).
	 *
	 * @var DateTimeImmutable
	 */
	private DateTimeImmutable $now;

	/**
	 * Constructor.
	 *
	 * @param DateTimeImmutable $now Instant to freeze (converted to UTC).
	 *
	 * @throws \Bookline\Domain\Shared\DomainException When invariants fail.
	 */
	public function __construct( DateTimeImmutable $now ) {
		$this->now = $now->setTimezone( new DateTimeZone( 'UTC' ) );
	}

	/**
	 * Current instant in UTC.
	 *
	 * {@inheritDoc}
	 *
	 * @since 0.1.0
	 */
	public function now(): DateTimeImmutable {
		return $this->now;
	}

	/**
	 * Move the frozen clock forward (or backward with a negative modifier).
	 *
	 * @param string $modifier DateInterval-compatible relative string, e.g. '+1 hour'.
	 *
	 * @since 0.1.0
	 */
	public function advance( string $modifier ): void {
		$this->now = $this->now->modify( $modifier )->setTimezone( new DateTimeZone( 'UTC' ) );
	}

	/**
	 * Replace the frozen instant.
	 *
	 * @param DateTimeImmutable $now New instant.
	 *
	 * @since 0.1.0
	 */
	public function set( DateTimeImmutable $now ): void {
		$this->now = $now->setTimezone( new DateTimeZone( 'UTC' ) );
	}
}