Blocks/refactor twentytwentyone block processor (take 2)

src/wp-content/themes/twentytwentyone/inc/template-functions.php

@@ -361,44 +361,49 @@ function twenty_twenty_one_get_non_latin_css( $type = 'front-end' ) {
  * @return bool Returns true if a block was located & printed, otherwise false.
  */
 function twenty_twenty_one_print_first_instance_of_block( $block_name, $content = null, $instances = 1 ) {
-	$instances_count = 0;
-	$blocks_content  = '';
+	// Scan for blocks whose block type matches the prefix, if provided a wildcard.
+	$prefix         = rtrim( $block_name, '*' );
+	$match_fully    = $prefix === $block_name;
+	$blocks_content = '';
+	$instance_count = 0;
 
 	if ( ! $content ) {
 		$content = get_the_content();
 	}
 
-	// Parse blocks in the content.
-	$blocks = parse_blocks( $content );
-
-	// Loop blocks.
-	foreach ( $blocks as $block ) {
-
-		// Confidence check.
-		if ( ! isset( $block['blockName'] ) ) {
-			continue;
-		}
-
-		// Check if this the block matches the $block_name.
-		$is_matching_block = false;
-
-		// If the block ends with *, try to match the first portion.
-		if ( '*' === $block_name[-1] ) {
-			$is_matching_block = 0 === strpos( $block['blockName'], rtrim( $block_name, '*' ) );
-		} else {
-			$is_matching_block = $block_name === $block['blockName'];
+	// Loop over top-level blocks.
+	if ( class_exists( '\WP_Block_Processor' ) ) {
+		$processor = new WP_Block_Processor( $content );
+
+		while ( $instance_count < $instances && $processor->next_block() ) {
+			if (
+				1 === $processor->get_depth() &&
+				/*
+				 * Prefix matches with a wildcard require printing the block name,
+				 * while full block-type matching can be delegated to the processor.
+				 * In each case, the condition only holds when the match is successful.
+				 */
+				$match_fully
+					? $processor->is_block_type( $block_name )
+					: str_starts_with( $processor->get_printable_block_type(), $prefix )
+			) {
+				$blocks_content .= render_block( $processor->extract_full_block_and_advance() );
+				++$instance_count;
+			}
 		}
-
-		if ( $is_matching_block ) {
-			// Increment count.
-			++$instances_count;
-
-			// Add the block HTML.
-			$blocks_content .= render_block( $block );
-
-			// Break the loop if the $instances count was reached.
-			if ( $instances_count >= $instances ) {
-				break;
+	} else {
+		// Parse blocks in the content.
+		$blocks = parse_blocks( $content );
+
+		// Loop top-level blocks, releasing them from memory as soon as possible.
+		while ( $instance_count < $instances && null !== ( $block = array_shift( $blocks ) ) ) {
+			if (
+				$match_fully
+					? $block_name === $block['blockName']
+					: str_starts_with( $block['blockName'] ?? '', $prefix )
+			) {
+				$blocks_content .= render_block( $block );
+				++$instance_count;
 			}
 		}
 	}