class FieldBlock

class FieldBlock extends BlockBase implements ContextAwarePluginInterface, ContainerFactoryPluginInterface {
  
  /**
   * The entity field manager.
   *
   * @var \Drupal\Core\Entity\EntityFieldManagerInterface
   */
  protected $entityFieldManager;
  
  /**
   * The formatter manager.
   *
   * @var \Drupal\Core\Field\FormatterPluginManager
   */
  protected $formatterManager;
  
  /**
   * The entity type ID.
   *
   * @var string
   */
  protected $entityTypeId;
  
  /**
   * The bundle ID.
   *
   * @var string
   */
  protected $bundle;
  
  /**
   * The field name.
   *
   * @var string
   */
  protected $fieldName;
  
  /**
   * The field definition.
   *
   * @var \Drupal\Core\Field\FieldDefinitionInterface
   */
  protected $fieldDefinition;
  
  /**
   * The module handler.
   *
   * @var \Drupal\Core\Extension\ModuleHandlerInterface
   */
  protected $moduleHandler;
  
  /**
   * The logger.
   *
   * @var \Psr\Log\LoggerInterface
   */
  protected $logger;
  
  /**
   * Constructs a new FieldBlock.
   *
   * @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\EntityFieldManagerInterface $entity_field_manager
   *   The entity field manager.
   * @param \Drupal\Core\Field\FormatterPluginManager $formatter_manager
   *   The formatter manager.
   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
   *   The module handler.
   * @param \Psr\Log\LoggerInterface $logger
   *   The logger.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityFieldManagerInterface $entity_field_manager, FormatterPluginManager $formatter_manager, ModuleHandlerInterface $module_handler, LoggerInterface $logger) {
    $this->entityFieldManager = $entity_field_manager;
    $this->formatterManager = $formatter_manager;
    $this->moduleHandler = $module_handler;
    $this->logger = $logger;
    // Get the entity type and field name from the plugin ID.
    list(, $entity_type_id, $bundle, $field_name) = explode(static::DERIVATIVE_SEPARATOR, $plugin_id, 4);
    $this->entityTypeId = $entity_type_id;
    $this->bundle = $bundle;
    $this->fieldName = $field_name;
    parent::__construct($configuration, $plugin_id, $plugin_definition);
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($configuration, $plugin_id, $plugin_definition, $container->get('entity_field.manager'), $container->get('plugin.manager.field.formatter'), $container->get('module_handler'), $container->get('logger.channel.layout_builder'));
  }
  
  /**
   * Gets the entity that has the field.
   *
   * @return \Drupal\Core\Entity\FieldableEntityInterface
   *   The entity.
   */
  protected function getEntity() {
    return $this->getContextValue('entity');
  }
  
  /**
   * {@inheritdoc}
   */
  public function build() {
    $display_settings = $this->getConfiguration()['formatter'];
    $display_settings['third_party_settings']['layout_builder']['view_mode'] = $this->getContextValue('view_mode');
    $entity = $this->getEntity();
    try {
      $build = $entity->get($this->fieldName)
        ->view($display_settings);
    } catch (EnforcedResponseException $e) {
      throw $e;
    } catch (\Exception $e) {
      $build = [];
      $this->logger
        ->warning('The field "%field" failed to render with the error of "%error".', [
        '%field' => $this->fieldName,
        '%error' => $e->getMessage(),
      ]);
    }
    CacheableMetadata::createFromRenderArray($build)->addCacheableDependency($this)
      ->applyTo($build);
    return $build;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getPreviewFallbackString() {
    return new TranslatableMarkup('"@field" field', [
      '@field' => $this->getFieldDefinition()
        ->getLabel(),
    ]);
  }
  
  /**
   * {@inheritdoc}
   */
  protected function blockAccess(AccountInterface $account) {
    $entity = $this->getEntity();
    // First consult the entity.
    $access = $entity->access('view', $account, TRUE);
    if (!$access->isAllowed()) {
      return $access;
    }
    // Check that the entity in question has this field.
    if (!$entity instanceof FieldableEntityInterface || !$entity->hasField($this->fieldName)) {
      return $access->andIf(AccessResult::forbidden());
    }
    // Check field access.
    $field = $entity->get($this->fieldName);
    $access = $access->andIf($field->access('view', $account, TRUE));
    if (!$access->isAllowed()) {
      return $access;
    }
    // Check to see if the field has any values.
    if ($field->isEmpty()) {
      return $access->andIf(AccessResult::forbidden());
    }
    return $access;
  }
  
  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    return [
      'label_display' => FALSE,
      'formatter' => [
        'label' => 'above',
        'type' => $this->pluginDefinition['default_formatter'],
        'settings' => [],
        'third_party_settings' => [],
      ],
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function blockForm($form, FormStateInterface $form_state) {
    $config = $this->getConfiguration();
    $form['formatter'] = [
      '#tree' => TRUE,
      '#process' => [
        [
          $this,
          'formatterSettingsProcessCallback',
        ],
      ],
    ];
    $form['formatter']['label'] = [
      '#type' => 'select',
      '#title' => $this->t('Label'),
      // @todo This is directly copied from
      //   \Drupal\field_ui\Form\EntityViewDisplayEditForm::getFieldLabelOptions(),
      //   resolve this in https://www.drupal.org/project/drupal/issues/2933924.
'#options' => [
        'above' => $this->t('Above'),
        'inline' => $this->t('Inline'),
        'hidden' => '- ' . $this->t('Hidden') . ' -',
        'visually_hidden' => '- ' . $this->t('Visually Hidden') . ' -',
      ],
      '#default_value' => $config['formatter']['label'],
    ];
    $form['formatter']['type'] = [
      '#type' => 'select',
      '#title' => $this->t('Formatter'),
      '#options' => $this->getApplicablePluginOptions($this->getFieldDefinition()),
      '#required' => TRUE,
      '#default_value' => $config['formatter']['type'],
      '#ajax' => [
        'callback' => [
          static::class,
          'formatterSettingsAjaxCallback',
        ],
        'wrapper' => 'formatter-settings-wrapper',
      ],
    ];
    // Add the formatter settings to the form via AJAX.
    $form['formatter']['settings_wrapper'] = [
      '#prefix' => '<div id="formatter-settings-wrapper">',
      '#suffix' => '</div>',
    ];
    return $form;
  }
  
  /**
   * Render API callback: builds the formatter settings elements.
   */
  public function formatterSettingsProcessCallback(array &$element, FormStateInterface $form_state, array &$complete_form) {
    if ($formatter = $this->getFormatter($element['#parents'], $form_state)) {
      $element['settings_wrapper']['settings'] = $formatter->settingsForm($complete_form, $form_state);
      $element['settings_wrapper']['settings']['#parents'] = array_merge($element['#parents'], [
        'settings',
      ]);
      $element['settings_wrapper']['third_party_settings'] = $this->thirdPartySettingsForm($formatter, $this->getFieldDefinition(), $complete_form, $form_state);
      $element['settings_wrapper']['third_party_settings']['#parents'] = array_merge($element['#parents'], [
        'third_party_settings',
      ]);
      FormHelper::rewriteStatesSelector($element['settings_wrapper'], "fields[{$this->fieldName}][settings_edit_form]", 'settings[formatter]');
      // Store the array parents for our element so that we can retrieve the
      // formatter settings in our AJAX callback.
      $form_state->set('field_block_array_parents', $element['#array_parents']);
    }
    return $element;
  }
  
  /**
   * Adds the formatter third party settings forms.
   *
   * @param \Drupal\Core\Field\FormatterInterface $plugin
   *   The formatter.
   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
   *   The field definition.
   * @param array $form
   *   The (entire) configuration form array.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The form state.
   *
   * @return array
   *   The formatter third party settings form.
   */
  protected function thirdPartySettingsForm(FormatterInterface $plugin, FieldDefinitionInterface $field_definition, array $form, FormStateInterface $form_state) {
    $settings_form = [];
    // Invoke hook_field_formatter_third_party_settings_form(), keying resulting
    // subforms by module name.
    foreach ($this->moduleHandler
      ->getImplementations('field_formatter_third_party_settings_form') as $module) {
      $settings_form[$module] = $this->moduleHandler
        ->invoke($module, 'field_formatter_third_party_settings_form', [
        $plugin,
        $field_definition,
        EntityDisplayBase::CUSTOM_MODE,
        $form,
        $form_state,
      ]);
    }
    return $settings_form;
  }
  
  /**
   * Render API callback: gets the layout settings elements.
   */
  public static function formatterSettingsAjaxCallback(array $form, FormStateInterface $form_state) {
    $formatter_array_parents = $form_state->get('field_block_array_parents');
    return NestedArray::getValue($form, array_merge($formatter_array_parents, [
      'settings_wrapper',
    ]));
  }
  
  /**
   * {@inheritdoc}
   */
  public function blockSubmit($form, FormStateInterface $form_state) {
    $this->configuration['formatter'] = $form_state->getValue('formatter');
  }
  
  /**
   * Gets the field definition.
   *
   * @return \Drupal\Core\Field\FieldDefinitionInterface
   *   The field definition.
   */
  protected function getFieldDefinition() {
    if (empty($this->fieldDefinition)) {
      $field_definitions = $this->entityFieldManager
        ->getFieldDefinitions($this->entityTypeId, $this->bundle);
      $this->fieldDefinition = $field_definitions[$this->fieldName];
    }
    return $this->fieldDefinition;
  }
  
  /**
   * Returns an array of applicable formatter options for a field.
   *
   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
   *   The field definition.
   *
   * @return array
   *   An array of applicable formatter options.
   *
   * @see \Drupal\field_ui\Form\EntityDisplayFormBase::getApplicablePluginOptions()
   */
  protected function getApplicablePluginOptions(FieldDefinitionInterface $field_definition) {
    $options = $this->formatterManager
      ->getOptions($field_definition->getType());
    $applicable_options = [];
    foreach ($options as $option => $label) {
      $plugin_class = DefaultFactory::getPluginClass($option, $this->formatterManager
        ->getDefinition($option));
      if ($plugin_class::isApplicable($field_definition)) {
        $applicable_options[$option] = $label;
      }
    }
    return $applicable_options;
  }
  
  /**
   * Gets the formatter object.
   *
   * @param array $parents
   *   The #parents of the element representing the formatter.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @return \Drupal\Core\Field\FormatterInterface
   *   The formatter object.
   */
  protected function getFormatter(array $parents, FormStateInterface $form_state) {
    // Use the processed values, if available.
    $configuration = NestedArray::getValue($form_state->getValues(), $parents);
    if (!$configuration) {
      // Next check the raw user input.
      $configuration = NestedArray::getValue($form_state->getUserInput(), $parents);
      if (!$configuration) {
        // If no user input exists, use the default values.
        $configuration = $this->getConfiguration()['formatter'];
      }
    }
    return $this->formatterManager
      ->getInstance([
      'configuration' => $configuration,
      'field_definition' => $this->getFieldDefinition(),
      'view_mode' => EntityDisplayBase::CUSTOM_MODE,
      'prepare' => TRUE,
    ]);
  }

}