WP_HTML_Tag_Processor

Adds a custom class to the block wrapper DIV

<?php

namespace SayHello\Theme\Blocks\CoreGroup;

use WP_HTML_Tag_Processor;

class Block
{

	/**
	 * Initialize the controller by registering actions and filters.
	 *
	 * @return void
	 */
	public function run(): void
	{
		add_filter('render_block_core/group', [$this, 'blockGapClass'], 10, 2);
	}

	/**
	 * Adds a custom class to the group block if a custom block gap is set.
	 *
	 * @param string $html The HTML of the block.
	 * @param array $block The block data.
	 * @return string The modified HTML of the block.
	 */
	public function blockGapClass(string $html, array $block): string
	{

		$blockGap = false;

		if (
			isset($block['attrs']) && is_array($block['attrs']) &&
			isset($block['attrs']['style']) && is_array($block['attrs']['style']) &&
			isset($block['attrs']['style']['spacing']) && is_array($block['attrs']['style']['spacing']) &&
			isset($block['attrs']['style']['spacing']['blockGap'])
		) {
			$blockGap = $block['attrs']['style']['spacing']['blockGap'];
		}

		if (!$blockGap) {
			return $html;
		}

		$processor = new WP_HTML_Tag_Processor($html);
		if ($processor->next_tag(['class_name' => 'wp-block-group'])) {
			$processor->add_class('wp-block-group--sht-custom-block-gap');
			return $processor->get_updated_html();
		}

		return $html;
	}
}