class EntityView

class EntityView extends BlockBase implements ContextAwarePluginInterface, ContainerFactoryPluginInterface {
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * The entity display repository.
     *
     * @var \Drupal\Core\Entity\EntityDisplayRepositoryInterface
     */
    protected $entityDisplayRepository;
    
    /**
     * Constructs a new EntityView.
     *
     * @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\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\Core\Entity\EntityDisplayRepositoryInterface $entity_display_repository
     *   The entity display repository.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager, EntityDisplayRepositoryInterface $entity_display_repository) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->entityTypeManager = $entity_type_manager;
        $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('entity_type.manager'), $container->get('entity_display.repository'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return [
            'view_mode' => 'default',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function blockForm($form, FormStateInterface $form_state) {
        $form['view_mode'] = [
            '#type' => 'select',
            '#options' => $this->entityDisplayRepository
                ->getViewModeOptions($this->getDerivativeId()),
            '#title' => $this->t('View mode'),
            '#default_value' => $this->configuration['view_mode'],
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function blockSubmit($form, FormStateInterface $form_state) {
        $this->configuration['view_mode'] = $form_state->getValue('view_mode');
    }
    
    /**
     * {@inheritdoc}
     */
    public function access(AccountInterface $account, $return_as_object = FALSE) {
        // Check the parent's access.
        $parent_access = parent::access($account, TRUE);
        if (!$parent_access->isAllowed()) {
            return $return_as_object ? $parent_access : $parent_access->isAllowed();
        }
        
        /** @var \Drupal\Core\Entity\EntityInterface $entity */
        $entity = $this->getContextValue('entity');
        return $entity->access('view', $account, $return_as_object);
    }
    
    /**
     * {@inheritdoc}
     */
    public function build() {
        
        /** @var \Drupal\Core\Entity\EntityInterface $entity */
        $entity = $this->getContextValue('entity');
        $view_builder = $this->entityTypeManager
            ->getViewBuilder($entity->getEntityTypeId());
        $build = $view_builder->view($entity, $this->configuration['view_mode']);
        CacheableMetadata::createFromObject($entity)->merge(CacheableMetadata::createFromRenderArray($build))
            ->applyTo($build);
        return $build;
    }

}