class BlockContentBlock

class BlockContentBlock extends BlockBase implements ContainerFactoryPluginInterface {
  
  /**
   * The Plugin Block Manager.
   *
   * @var \Drupal\Core\Block\BlockManagerInterface
   */
  protected $blockManager;
  
  /**
   * The entity type manager service.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;
  
  /**
   * The Drupal account to use for checking for access to block.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $account;
  
  /**
   * The block content entity.
   *
   * @var \Drupal\block_content\BlockContentInterface
   */
  protected $blockContent;
  
  /**
   * The URL generator.
   *
   * @var \Drupal\Core\Routing\UrlGeneratorInterface
   */
  protected $urlGenerator;
  
  /**
   * The block content UUID lookup service.
   *
   * @var \Drupal\block_content\BlockContentUuidLookup
   */
  protected $uuidLookup;
  
  /**
   * The entity display repository.
   *
   * @var \Drupal\Core\Entity\EntityDisplayRepositoryInterface
   */
  protected $entityDisplayRepository;
  
  /**
   * Constructs a new BlockContentBlock.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin ID for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Block\BlockManagerInterface $block_manager
   *   The Plugin Block Manager.
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager service.
   * @param \Drupal\Core\Session\AccountInterface $account
   *   The account for which view access should be checked.
   * @param \Drupal\Core\Routing\UrlGeneratorInterface $url_generator
   *   The URL generator.
   * @param \Drupal\block_content\BlockContentUuidLookup $uuid_lookup
   *   The block content UUID lookup service.
   * @param \Drupal\Core\Entity\EntityDisplayRepositoryInterface $entity_display_repository
   *   The entity display repository.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, BlockManagerInterface $block_manager, EntityTypeManagerInterface $entity_type_manager, AccountInterface $account, UrlGeneratorInterface $url_generator, BlockContentUuidLookup $uuid_lookup, EntityDisplayRepositoryInterface $entity_display_repository) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->blockManager = $block_manager;
    $this->entityTypeManager = $entity_type_manager;
    $this->account = $account;
    $this->urlGenerator = $url_generator;
    $this->uuidLookup = $uuid_lookup;
    $this->entityDisplayRepository = $entity_display_repository;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($configuration, $plugin_id, $plugin_definition, $container->get('plugin.manager.block'), $container->get('entity_type.manager'), $container->get('current_user'), $container->get('url_generator'), $container->get('block_content.uuid_lookup'), $container->get('entity_display.repository'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    return [
      'status' => TRUE,
      'info' => '',
      'view_mode' => 'full',
    ];
  }
  
  /**
   * Overrides \Drupal\Core\Block\BlockBase::blockForm().
   *
   * Adds body and description fields to the block configuration form.
   */
  public function blockForm($form, FormStateInterface $form_state) {
    $block = $this->getEntity();
    if (!$block) {
      return $form;
    }
    $options = $this->entityDisplayRepository
      ->getViewModeOptionsByBundle('block_content', $block->bundle());
    $form['view_mode'] = [
      '#type' => 'select',
      '#options' => $options,
      '#title' => $this->t('View mode'),
      '#description' => $this->t('Output the block in this view mode.'),
      '#default_value' => $this->configuration['view_mode'],
      '#access' => count($options) > 1,
    ];
    $form['title']['#description'] = $this->t('The title of the block as shown to the user.');
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function blockSubmit($form, FormStateInterface $form_state) {
    // Invalidate the block cache to update content block-based derivatives.
    $this->configuration['view_mode'] = $form_state->getValue('view_mode');
    $this->blockManager
      ->clearCachedDefinitions();
  }
  
  /**
   * {@inheritdoc}
   */
  protected function blockAccess(AccountInterface $account) {
    if ($this->getEntity()) {
      return $this->getEntity()
        ->access('view', $account, TRUE);
    }
    return AccessResult::forbidden();
  }
  
  /**
   * {@inheritdoc}
   */
  public function build() {
    if ($block = $this->getEntity()) {
      return $this->entityTypeManager
        ->getViewBuilder($block->getEntityTypeId())
        ->view($block, $this->configuration['view_mode']);
    }
    else {
      return [
        '#markup' => $this->t('Block with uuid %uuid does not exist. <a href=":url">Add content block</a>.', [
          '%uuid' => $this->getDerivativeId(),
          ':url' => $this->urlGenerator
            ->generate('block_content.add_page'),
        ]),
        '#access' => $this->account
          ->hasPermission('administer blocks'),
      ];
    }
  }
  
  /**
   * Loads the block content entity of the block.
   *
   * @return \Drupal\block_content\BlockContentInterface|null
   *   The block content entity.
   */
  protected function getEntity() {
    if (!isset($this->blockContent)) {
      $uuid = $this->getDerivativeId();
      if ($id = $this->uuidLookup
        ->get($uuid)) {
        $this->blockContent = $this->entityTypeManager
          ->getStorage('block_content')
          ->load($id);
      }
    }
    return $this->blockContent;
  }

}