FEATURE: Add ClosureProjection

src/Projection/ClosureProjection.php

@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Wwwision\DCBLibrary\Projection;
+
+use Wwwision\DCBEventStore\Types\EventEnvelope;
+use Wwwision\DCBEventStore\Types\EventTypes;
+use Wwwision\DCBLibrary\DomainEvent;
+use Wwwision\DCBLibrary\EventTypesAware;
+
+/**
+ * @template S
+ * @implements Projection<S>
+ */
+final class ClosureProjection implements Projection, EventTypesAware
+{
+    /**
+     * @param S $initialState
+     * @param array<class-string, callable> $handlers
+     */
+    private function __construct(
+        private readonly mixed $initialState,
+        public readonly array $handlers,
+    ) {
+    }
+
+    /**
+     * @template PS
+     * @param PS $initialState
+     * @return self<PS>
+     */
+    public static function create(mixed $initialState): self
+    {
+        return new self($initialState, []);
+    }
+
+    /**
+     * @template E of DomainEvent
+     * @param class-string<E> $class
+     * @param callable(S, E): S $cb
+     * @return self<S>
+     */
+    public function when(string $class, callable $cb): self
+    {
+        return new self($this->initialState, [...$this->handlers, $class => $cb]);
+    }
+
+    public function eventTypes(): EventTypes
+    {
+        return EventTypes::fromStrings(...array_map(static fn($domainEventClassName) => substr($domainEventClassName, strrpos($domainEventClassName, '\\') + 1), array_keys($this->handlers)));
+    }
+
+    /**
+     * @return S
+     */
+    public function initialState(): mixed
+    {
+        return $this->initialState;
+    }
+
+    /**
+     * @param S $state
+     * @return S
+     */
+    public function apply(mixed $state, DomainEvent $domainEvent, EventEnvelope $eventEnvelope): mixed
+    {
+        if (!array_key_exists($domainEvent::class, $this->handlers)) {
+            return $state;
+        }
+        return $this->handlers[$domainEvent::class]($state, $domainEvent, $eventEnvelope);
+    }
+}