feat: add content handler registry

tests/Unit/Content/ContentHandlerRegistryTest.php

@@ -0,0 +1,54 @@
+<?php
+/**
+ * Tests for content handler registry.
+ *
+ * @package WPContentSync
+ */
+
+namespace WPContentSync\Tests\Unit\Content;
+
+use PHPUnit\Framework\TestCase;
+use WPContentSync\Content\ContentHandlerInterface;
+use WPContentSync\Content\ContentHandlerRegistry;
+use WPContentSync\Sync\SyncContext;
+use WPContentSync\Sync\SyncResult;
+
+class ContentHandlerRegistryTest extends TestCase {
+	public function test_it_returns_handlers_in_package_order(): void {
+		$posts = $this->handler( 'posts' );
+		$terms = $this->handler( 'terms' );
+		$media = $this->handler( 'media' );
+
+		$registry = new ContentHandlerRegistry( array( $media, $posts, $terms ) );
+
+		self::assertSame( array( $terms, $posts, $media ), $registry->ordered() );
+	}
+
+	public function test_it_rejects_duplicate_buckets(): void {
+		$this->expectException( \InvalidArgumentException::class );
+		$this->expectExceptionMessage( 'Handler bucket "posts" is already registered.' );
+
+		new ContentHandlerRegistry( array( $this->handler( 'posts' ), $this->handler( 'posts' ) ) );
+	}
+
+	private function handler( string $bucket ): ContentHandlerInterface {
+		return new class( $bucket ) implements ContentHandlerInterface {
+			private string $bucket;
+
+			public function __construct( string $bucket ) {
+				$this->bucket = $bucket;
+			}
+
+			public function bucket(): string {
+				return $this->bucket;
+			}
+
+			/**
+			 * @param array<int, array<string, mixed>> $records Package records.
+			 */
+			public function importRecords( array $records, SyncContext $context ): SyncResult {
+				return SyncResult::success( array( 'skipped' => count( $records ) ) );
+			}
+		};
+	}
+}