Issue #3269359 by RenatoG: Store the block class in a config to be used in the auto-complete

use Drupal\block\Entity\Block;

use Drupal\Component\Utility\Html;

use Drupal\block_class\Constants\BlockClassConstants;

use Drupal\Component\Serialization\Json;

/**

 * Block Class Service Class.

    // Set the Third Party Settings.

    $entity->setThirdPartySetting('block_class', 'classes', $block_classes);

    // Get the config object.

    $config = $this->configFactory->getEditable('block_class.settings');

    // Get the current classes stored.

    $block_classes_stored = $config->get('block_classes_stored');

    // Get the array from JSON.

    $block_classes_stored = Json::decode($block_classes_stored);

    // Verify if is empty.

    if (empty($block_classes_stored)) {

      $block_classes_stored = [];

    }

    // Get the current class and export to array.

    $current_block_classes = explode(' ', $block_classes);

    // Use the key the same as value.

    $current_block_classes = array_combine($current_block_classes, $current_block_classes);

    // Merge with the current one.

    $block_classes_to_store = array_merge($current_block_classes, $current_block_classes);

    // Get as JSON.

    $block_classes_to_store = Json::encode($block_classes_to_store);

    // Store in the config.

    $config->set('block_classes_stored', $block_classes_to_store);

    // Save.

    $config->save();

  }

  /**