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<?php
namespace MediaWiki\DomainEvent;
use LogicException;
use MediaWiki\Utils\MWTimestamp;
use Wikimedia\Timestamp\ConvertibleTimestamp;
/**
* Base class for domain event objects to be used with DomainEventDispatcher.
*
* Domain events are used to notify other parts of the code (oder "domains")
* about a change to the persistent state of the local wiki.
*
* The idea of domain events is borrowed from the Domain Driven Design paradigm.
* For a thorough explanation, see
* <https://learn.microsoft.com/en-us/dotnet/architecture/microservices/microservice-ddd-cqrs-patterns/domain-events-design-implementation>.
* Also compare <https://martinfowler.com/eaaDev/DomainEvent.html>.
*
* Domain event objects must be immutable.
*
* An event object should contain all information that was used to affect that
* change (the command parameters) as well as information representing the
* outcome of the change.
*
* @note Subclasses must call declareEventType() in their constructor!
*
* @since 1.44
* @unstable until 1.45, should become stable to extend
*/
abstract class DomainEvent {
public const ANY = '*';
private string $eventType = self::ANY;
private array $compatibleWithTypes = [ self::ANY ];
private ConvertibleTimestamp $timestamp;
private bool $isReconciliationRequest;
/**
* @stable to call
*
* @param string|ConvertibleTimestamp|false $timestamp
* @param bool $isReconciliationRequest see isReconciliationRequest()
*/
public function __construct( $timestamp = false, bool $isReconciliationRequest = false ) {
$this->timestamp = $timestamp instanceof ConvertibleTimestamp
? $timestamp
: MWTimestamp::getInstance( $timestamp );
$this->isReconciliationRequest = $isReconciliationRequest;
}
/**
* Determines whether this is a reconciliation event, triggered artificially
* in order to give listeners an opportunity to catch up on missed events or
* recreate corrupted data.
*
* Reconciliation requests are typically issued by maintenance scripts,
* but can also be caused by user actions such as null-edits.
*/
public function isReconciliationRequest(): bool {
return $this->isReconciliationRequest;
}
/**
* Declares the event type. Must be called from the constructors of
* all subclasses of DomainEvent!
*
* @param string $eventType
*/
protected function declareEventType( string $eventType ) {
$this->eventType = $eventType;
$this->compatibleWithTypes[] = $eventType;
}
/**
* Returns this event's type.
*/
public function getEventType(): string {
if ( $this->eventType === self::ANY ) {
throw new LogicException(
'Constructor did not call the declareEventType() method!'
);
}
return $this->eventType;
}
/**
* Returns the event types this event is compatible with.
*
* @internal for use in EventDispatchEngine.
*
* @return array An array containing the event's type and all parent types.
*/
public function getEventTypeChain(): array {
if ( count( $this->compatibleWithTypes ) < 2 ) {
throw new LogicException(
'Constructor did not call the declareEventType() method!'
);
}
return $this->compatibleWithTypes;
}
/**
* Returns the time at which the event was emitted.
*/
public function getEventTimestamp(): ConvertibleTimestamp {
return $this->timestamp;
}
}
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