add trigger subscription engine event bus

docs/pages/getting_started.md

@@ -275,6 +275,7 @@ use Patchlevel\EventSourcing\Repository\DefaultRepositoryManager;
 use Patchlevel\EventSourcing\Serializer\DefaultEventSerializer;
 use Patchlevel\EventSourcing\Store\DoctrineDbalStore;
 use Patchlevel\EventSourcing\Subscription\Engine\DefaultSubscriptionEngine;
+use Patchlevel\EventSourcing\Subscription\Engine\RunSubscriptionEngineEventBus;
 use Patchlevel\EventSourcing\Subscription\Store\DoctrineSubscriptionStore;
 use Patchlevel\EventSourcing\Subscription\Subscriber\MetadataSubscriberAccessorRepository;
 
@@ -311,6 +312,7 @@ $engine = new DefaultSubscriptionEngine(
 $repositoryManager = new DefaultRepositoryManager(
     $aggregateRegistry,
     $eventStore,
+    new RunSubscriptionEngineEventBus($engine),
 );
 
 $hotelRepository = $repositoryManager->get(Hotel::class);
@@ -375,15 +377,8 @@ $hotel2 = $hotelRepository->load(Uuid::fromString('d0d0d0d0-d0d0-d0d0-d0d0-d0d0d
 $hotel2->checkIn('David');
 $hotelRepository->save($hotel2);
 
-/** @var SubscriptionEngine $engine */
-$engine->run();
-
 $hotels = $hotelProjection->getHotels();
 ```
-!!! warning
-
-    You need to run the subscription engine to update the projections and execute the processors.
-
 !!! note
 
     You can also use other forms of IDs such as uuid version 6 or a custom format. 

src/EventBus/ChainEventBus.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\EventSourcing\EventBus;
+
+use Patchlevel\EventSourcing\Message\Message;
+
+use function array_values;
+
+final class ChainEventBus implements EventBus
+{
+    /** @var list<EventBus> */
+    private readonly array $eventBus;
+
+    public function __construct(
+        EventBus ...$eventBus,
+    ) {
+        $this->eventBus = array_values($eventBus);
+    }
+
+    public function dispatch(Message ...$messages): void
+    {
+        foreach ($this->eventBus as $eventBus) {
+            $eventBus->dispatch(...$messages);
+        }
+    }
+}

src/Subscription/Engine/AlreadyProcessing.php

@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\EventSourcing\Subscription\Engine;
+
+use RuntimeException;
+
+final class AlreadyProcessing extends RuntimeException
+{
+    public function __construct()
+    {
+        parent::__construct('Subscription engine is already processing');
+    }
+}