CategoryAutocompleteController.php

<?php

namespace Drupal\block\Controller;

use Drupal\Component\Utility\Html;
use Drupal\Core\Block\BlockManagerInterface;
use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Symfony\Component\HttpFoundation\JsonResponse;
use Symfony\Component\HttpFoundation\Request;

/**
 * Returns autocomplete responses for block categories.
 */
class CategoryAutocompleteController implements ContainerInjectionInterface {

  /**
   * The block manager.
   *
   * @var \Drupal\Core\Block\BlockManagerInterface
   */
  protected $blockManager;

  /**
   * Constructs a new CategoryAutocompleteController.
   *
   * @param \Drupal\Core\Block\BlockManagerInterface $block_manager
   *   The block manager.
   */
  public function __construct(BlockManagerInterface $block_manager) {
    $this->blockManager = $block_manager;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container
      ->get('plugin.manager.block'));
  }

  /**
   * Retrieves suggestions for block category autocompletion.
   *
   * @param \Symfony\Component\HttpFoundation\Request $request
   *   The current request.
   *
   * @return \Symfony\Component\HttpFoundation\JsonResponse
   *   A JSON response containing autocomplete suggestions.
   */
  public function autocomplete(Request $request) {
    $typed_category = $request->query
      ->get('q');
    $matches = [];
    foreach ($this->blockManager
      ->getCategories() as $category) {
      if (stripos($category, $typed_category) === 0) {
        $matches[] = [
          'value' => $category,
          'label' => Html::escape($category),
        ];
      }
    }
    return new JsonResponse($matches);
  }

}