has_block()

function has_block( $block_name, $post = null ) {
	if ( ! has_blocks( $post ) ) {
		return false;
	}

	if ( ! is_string( $post ) ) {
		$gc_post = get_post( $post );
		if ( $gc_post instanceof GC_Post ) {
			$post = $gc_post->post_content;
		}
	}

	/*
	 * Normalize block name to include namespace, if provided as non-namespaced.
	 * This matches behavior for GeChiUI 5.0.0 - 5.3.0 in matching blocks by
	 * their serialized names.
	 */
	if ( false === strpos( $block_name, '/' ) ) {
		$block_name = 'core/' . $block_name;
	}

	// Test for existence of block by its fully qualified name.
	$has_block = false !== strpos( $post, '<!-- gc:' . $block_name . ' ' );

	if ( ! $has_block ) {
		/*
		 * If the given block name would serialize to a different name, test for
		 * existence by the serialized form.
		 */
		$serialized_block_name = strip_core_block_namespace( $block_name );
		if ( $serialized_block_name !== $block_name ) {
			$has_block = false !== strpos( $post, '<!-- gc:' . $serialized_block_name . ' ' );
		}
	}

	return $has_block;
}

/**
 * Has block function which searches as well in reusable blocks.
 *
 * @param mixed $block_name Full Block type to look for.
 * @return bool
 */
function gcdocs_enhanced_has_block( $block_name ) {
	if ( has_block( $block_name ) ) {
		return true;
	}

	if ( has_block( 'core/block' ) ) {
		$content = get_post_field( 'post_content' );
		$blocks = parse_blocks( $content );
		return gcdocs_search_reusable_blocks_within_innerblocks( $blocks, $block_name );
	}

	return false;
}

/**
 * Search for the selected block within inner blocks.
 *
 * The helper function for gcdocs_enhanced_has_block() function.
 *
 * @param array $blocks Blocks to loop through.
 * @param string $block_name Full Block type to look for.
 * @return bool
 */
function gcdocs_search_reusable_blocks_within_innerblocks( $blocks, $block_name ) {
	foreach ( $blocks as $block ) {
		if ( isset( $block['innerBlocks'] ) && ! empty( $block['innerBlocks'] ) ) {
			gcdocs_search_reusable_blocks_within_innerblocks( $block['innerBlocks'], $block_name );
		} elseif ( 'core/block' === $block['blockName'] && ! empty( $block['attrs']['ref'] ) && has_block( $block_name, $block['attrs']['ref'] ) ) {
			return true;
		}
	}

	return false;
}