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 custom 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 custom 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;
    }

}