Add a domain event dispatcher service to decouple publishing from dis…

…patching (#15)

README.md

@@ -102,6 +102,51 @@ date/time, the reminder must also be modified. By implementing
 providing that the previous _ReminderDue_ event had not been published, it will
 be removed and superseded by the new _ReminderDue_ event.
 
+### Event dispatching
+
+By default only the DomainEvent is dispatched to the configured event bus.
+
+You can overwrite the default event dispatcher with your own implementation to 
+annotate the message before dispatching it, e.g. to add an envelope with custom stamps.
+
+Example:
+
+```yaml
+services:
+    headsnet_domain_events.domain_event_dispatcher_service:
+        class: App\Infrastructure\DomainEventDispatcher
+```
+
+```php
+class PersonCreated implements DomainEvent, AuditableEvent
+{
+    …
+}
+```
+
+```php
+class DomainEventDispatcher implements \Headsnet\DomainEventsBundle\EventSubscriber\DomainEventDispatcher
+{
+    private MessageBusInterface  $eventBus;
+
+    public function __construct(MessageBusInterface $eventBus)
+    {
+        $this->eventBus = $eventBus;
+    }
+
+    public function dispatch(DomainEvent $event): void
+    {
+        if ($event instanceof AuditableEvent) {
+            $this->eventBus->dispatch(
+                new Envelope($event, [new AuditStamp()])
+            );
+        } else {
+            $this->eventBus->dispatch($event);
+        }
+    }
+}
+```
+
 ### Messenger Component
 
 By default, the bundle expects a message bus called `messenger.bus.event` to be

src/DependencyInjection/HeadsnetDomainEventsExtension.php

@@ -42,7 +42,7 @@ public function load(array $configs, ContainerBuilder $container): void
     private function useCustomMessageBusIfSpecified(array $config, ContainerBuilder $container): void
     {
         if (isset($config['message_bus']['name'])) {
-            $definition = $container->getDefinition('headsnet_domain_events.event_subscriber.publisher');
+            $definition = $container->getDefinition('headsnet_domain_events.domain_event_dispatcher_service');
             $definition->replaceArgument(0, new Reference($config['message_bus']['name']));
         }
     }

src/EventSubscriber/DomainEventDispatcher.php

@@ -0,0 +1,20 @@
+<?php
+/*
+ * This file is part of the Symfony HeadsnetDomainEventsBundle.
+ *
+ * (c) Headstrong Internet Services Ltd 2020
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Headsnet\DomainEventsBundle\EventSubscriber;
+
+use Headsnet\DomainEventsBundle\Domain\Model\DomainEvent;
+
+interface DomainEventDispatcher
+{
+    public function dispatch(DomainEvent $event): void;
+}

src/EventSubscriber/NoEnvelopeDomainEventDispatcher.php

@@ -0,0 +1,34 @@
+<?php
+/*
+ * This file is part of the Symfony HeadsnetDomainEventsBundle.
+ *
+ * (c) Headstrong Internet Services Ltd 2020
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Headsnet\DomainEventsBundle\EventSubscriber;
+
+use Headsnet\DomainEventsBundle\Domain\Model\DomainEvent;
+use Symfony\Component\Messenger\MessageBusInterface;
+
+class NoEnvelopeDomainEventDispatcher implements DomainEventDispatcher
+{
+    /**
+     * @var MessageBusInterface
+     */
+    private $eventBus;
+
+    public function __construct(MessageBusInterface $eventBus)
+    {
+        $this->eventBus = $eventBus;
+    }
+
+    public function dispatch(DomainEvent $event): void
+    {
+        $this->eventBus->dispatch($event);
+    }
+}

src/EventSubscriber/PublishDomainEventSubscriber.php

@@ -21,15 +21,14 @@
 use Symfony\Component\HttpKernel\Event\TerminateEvent;
 use Symfony\Component\HttpKernel\KernelEvents;
 use Symfony\Component\Lock\LockFactory;
-use Symfony\Component\Messenger\MessageBusInterface;
 use Symfony\Component\Serializer\SerializerInterface;
 
 final class PublishDomainEventSubscriber implements EventSubscriberInterface
 {
     /**
-     * @var MessageBusInterface
+     * @var DomainEventDispatcher
      */
-    private $eventBus;
+    private $domainEventDispatcher;
 
     /**
      * @var EventStore
@@ -47,12 +46,12 @@ final class PublishDomainEventSubscriber implements EventSubscriberInterface
     private $lockFactory;
 
     public function __construct(
-        MessageBusInterface $eventBus,
+        DomainEventDispatcher $domainEventDispatcher,
         EventStore $eventStore,
         SerializerInterface $serializer,
         LockFactory $lockFactory
     ) {
-        $this->eventBus = $eventBus;
+        $this->domainEventDispatcher = $domainEventDispatcher;
         $this->eventStore = $eventStore;
         $this->serializer = $serializer;
         $this->lockFactory = $lockFactory;
@@ -102,7 +101,7 @@ private function publishEvent(StoredEvent $storedEvent): void
             );
             assert($domainEvent instanceof DomainEvent);
 
-            $this->eventBus->dispatch($domainEvent);
+            $this->domainEventDispatcher->dispatch($domainEvent);
             $this->eventStore->publish($storedEvent);
 
             $lock->release();

src/Resources/config/services.xml

@@ -20,10 +20,17 @@
         just configure the default lock using the framework bundle configuration -->
         <service id="headsnet_domain_events.lock_factory_service" alias="lock.factory"/>
 
+        <!-- Clients can override this to change the default domain event dispatcher -->
+        <service id="headsnet_domain_events.domain_event_dispatcher_service"
+                 class="Headsnet\DomainEventsBundle\EventSubscriber\NoEnvelopeDomainEventDispatcher"
+                 public="false">
+            <argument type="service" id="messenger.bus.event"/>
+        </service>
+
         <service id="headsnet_domain_events.event_subscriber.publisher"
                  class="Headsnet\DomainEventsBundle\EventSubscriber\PublishDomainEventSubscriber"
                  public="false">
-            <argument type="service" id="messenger.bus.event"/>
+            <argument type="service" id="headsnet_domain_events.domain_event_dispatcher_service"/>
             <argument type="service" id="headsnet_domain_events.repository.event_store_doctrine"/>
             <argument type="service" id="serializer"/>
             <argument type="service" id="headsnet_domain_events.lock_factory_service"/>