class BlockContent

class BlockContent extends DeriverBase implements ContainerDeriverInterface {

  /**
   * The content block storage.
   *
   * @var \Drupal\Core\Entity\EntityStorageInterface
   */
  protected $blockContentStorage;

  /**
   * Constructs a BlockContent object.
   *
   * @param \Drupal\Core\Entity\EntityStorageInterface $block_content_storage
   *   The content block storage.
   */
  public function __construct(EntityStorageInterface $block_content_storage) {
    $this->blockContentStorage = $block_content_storage;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, $base_plugin_id) {
    $entity_type_manager = $container
      ->get('entity_type.manager');
    return new static($entity_type_manager
      ->getStorage('block_content'));
  }

  /**
   * {@inheritdoc}
   */
  public function getDerivativeDefinitions($base_plugin_definition) {
    $block_contents = $this->blockContentStorage
      ->loadByProperties([
      'reusable' => TRUE,
    ]);

    // Reset the discovered definitions.
    $this->derivatives = [];

    /** @var \Drupal\block_content\Entity\BlockContent $block_content */
    foreach ($block_contents as $block_content) {
      $this->derivatives[$block_content
        ->uuid()] = $base_plugin_definition;
      $this->derivatives[$block_content
        ->uuid()]['admin_label'] = $block_content
        ->label() ?? $block_content->type->entity
        ->label() . ': ' . $block_content
        ->id();
      $this->derivatives[$block_content
        ->uuid()]['config_dependencies']['content'] = [
        $block_content
          ->getConfigDependencyName(),
      ];
    }
    return parent::getDerivativeDefinitions($base_plugin_definition);
  }

}