Add a handy CallbackWriter to write with a Closure (#120)

* Add a handy CallbackWriter to write with a Closure

* Fixed missing comment on CallbackWriter

src/batch/docs/domain/item-job/item-writer.md

@@ -27,6 +27,8 @@ It can be any class implementing [ItemWriterInterface](../../../src/Job/Item/Ite
   write items to a job summary value.
 - [TransformingWriter](../../../src/Job/Item/Writer/TransformingWriter.php):
   perform items transformation before delegating to another writer.
+- [CallbackWriter](../../../src/Job/Item/Writer/CallbackWriter.php):
+  delegate items write operations to a closure passed at construction.
 
 **Item writers from bridges:**
 - [DispatchEachItemAsMessageWriter (`symfony/messenger`)](https://github.com/yokai-php/batch-symfony-messenger/blob/0.x/src/Writer/DispatchEachItemAsMessageWriter.php):

src/batch/src/Job/Item/Writer/CallbackWriter.php

@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yokai\Batch\Job\Item\Writer;
+
+use Yokai\Batch\Job\Item\ItemWriterInterface;
+
+/**
+ * An {@see ItemWriterInterface} that write items with a {@see Closure} provided at construction.
+ *
+ * Provided {@see Closure} must accept items to write and must return nothing.
+ */
+final class CallbackWriter implements ItemWriterInterface
+{
+    public function __construct(
+        private \Closure $callback,
+    ) {
+    }
+
+    public function write(iterable $items): void
+    {
+        ($this->callback)($items);
+    }
+}

src/batch/tests/Job/Item/Writer/CallbackWriterTest.php

@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yokai\Batch\Tests\Job\Item\Writer;
+
+use PHPUnit\Framework\TestCase;
+use Yokai\Batch\Job\Item\Writer\CallbackWriter;
+
+class CallbackWriterTest extends TestCase
+{
+    public function testWrite(): void
+    {
+        $saveditems = [];
+        $writer = new CallbackWriter(function (array $items) use (&$saveditems) {
+            $saveditems = [...$saveditems, ...$items];
+        });
+        $writer->write([1, 2, 3]);
+        $writer->write([4, 5, 6]);
+
+        self::assertSame([1, 2, 3, 4, 5, 6], $saveditems);
+    }
+}