Watch.php

<?php // Full license: https://gist.github.com/xphere/710839fba51cdd582ebd4ddf635cc0c4

use DateTimeImmutable as Time;

final class Watch
{
    /** @var Time|null */
    private static $frozenTime = null;

    public static function fromFormat($dateString, $format = 'Y-m-d H:i:s'): Time
    {
        return Time::createFromFormat($format, $dateString);
    }

    public static function now(): Time
    {
        return self::$frozenTime ?: new Time();
    }

    public static function at($time): Time
    {
        return self::$frozenTime
                ? self::$frozenTime->modify($time)
                : new Time($time);
    }

    public static function freeze(Time $time = null)
    {
        assert(null === self::$frozenTime);

        self::$frozenTime = $time ?: new Time();
    }

    public static function unfreeze()
    {
        self::$frozenTime = null;
    }

    // Avoid construction by making this private
    private function __construct()
    {
    }
}