Clock

We are using the clock to get the current datetime. This is needed to create the recorded_on datetime for the event stream. We have two implementations of the clock, one for the production and one for the tests. But you can also create your own implementation that is compatible with the PSR-20 clock specification.

SystemClock

This uses the native system clock to return the DateTimeImmutable instance.

use Patchlevel\EventSourcing\Clock\SystemClock;

$clock = new SystemClock();
$date = $clock->now(); // get the actual datetime
$date2 = $clock->now();

// $date == $date2 => false
// $date === $date2 => false

FrozenClock

This implementation should only be used for the tests. This enables you to freeze the time and with that to have deterministic tests.

use Patchlevel\EventSourcing\Clock\FrozenClock;

$date = new DateTimeImmutable();

$clock = new FrozenClock($date);
$frozenDate = $clock->now(); // gets the date provided before

// $date == $frozenDate => true
// $date === $frozenDate => false

The FrozenClock can also be updated with a new date, so you can test a jump in time.

use Patchlevel\EventSourcing\Clock\FrozenClock;

$firstDate = new DateTimeImmutable();
$clock = new FrozenClock($firstDate);

$secondDate = new DateTimeImmutable();
$clock->update($secondDate);

$frozenDate = $clock->now();

// $firstDate == $frozenDate => false
// $secondDate == $frozenDate => true

Or you can use the sleep method to simulate a time jump.

use Patchlevel\EventSourcing\Clock\FrozenClock;

$firstDate = new DateTimeImmutable();
$clock = new FrozenClock($firstDate);

$clock->sleep(10); // sleep 10 seconds

The instance of the frozen datetime will be cloned internally, so it's not the same instance but equal.

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