Add Block_Content_Filter library feature

src/features/library/class-block-content-filter.php

@@ -0,0 +1,61 @@
+<?php
+/**
+ * Block_Content_Filter class file
+ *
+ * @package wp-type-extensions
+ */
+
+namespace Alley\WP\Features\Library;
+
+use Alley\WP\Blocks\Block_Content;
+use Alley\WP\Types\Feature;
+use Alley\WP\Types\Serialized_Blocks;
+
+/**
+ * Filter block markup in 'the_content' for the post being viewed.
+ */
+final class Block_Content_Filter implements Feature {
+	/**
+	 * Callback to merge blocks.
+	 *
+	 * @var callable
+	 */
+	private $block_merge;
+
+	/**
+	 * Constructor.
+	 *
+	 * @phpstan-param callable(Serialized_Blocks $post_content): Serialized_Blocks $block_merge
+	 *
+	 * @param callable $block_merge Callback to merge blocks.
+	 */
+	public function __construct(
+		callable $block_merge,
+	) {
+		$this->block_merge = $block_merge;
+	}
+
+	/**
+	 * Boot the feature.
+	 */
+	public function boot(): void {
+		add_filter( 'the_content', [ $this, 'filter_the_content' ], 8 );
+	}
+
+	/**
+	 * Filters the post content.
+	 *
+	 * @param string $content Content of the current post.
+	 * @return string Updated content.
+	 */
+	public function filter_the_content( $content ) {
+		$post = get_post();
+
+		// Skip if 'the_content' is running on non-block content or on content other than the post being viewed.
+		if ( $post && is_single( $post->ID ) && has_blocks( $content ) ) {
+			$content = ( $this->block_merge )( new Block_Content( $content ) )->serialized_blocks();
+		}
+
+		return $content;
+	}
+}