class EntityViewDisplay

class EntityViewDisplay extends EntityDisplayBase implements EntityViewDisplayInterface {
    
    /**
     * {@inheritdoc}
     */
    protected $displayContext = 'view';
    
    /**
     * Returns the display objects used to render a set of entities.
     *
     * Depending on the configuration of the view mode for each bundle, this can
     * be either the display object associated with the view mode, or the
     * 'default' display.
     *
     * This method should only be used internally when rendering an entity. When
     * assigning suggested display options for a component in a given view mode,
     * EntityDisplayRepositoryInterface::getViewDisplay() should be used instead,
     * in order to avoid inadvertently modifying the output of other view modes
     * that might happen to use the 'default' display too. Those options will then
     * be effectively applied only if the view mode is configured to use them.
     *
     * hook_entity_view_display_alter() is invoked on each display, allowing 3rd
     * party code to alter the display options held in the display before they are
     * used to generate render arrays.
     *
     * @param \Drupal\Core\Entity\FieldableEntityInterface[] $entities
     *   The entities being rendered. They should all be of the same entity type.
     * @param string $view_mode
     *   The view mode being rendered.
     *
     * @return \Drupal\Core\Entity\Display\EntityViewDisplayInterface[]
     *   The display objects to use to render the entities, keyed by entity
     *   bundle.
     *
     * @see \Drupal\Core\Entity\EntityDisplayRepositoryInterface::getViewDisplay()
     * @see hook_entity_view_display_alter()
     */
    public static function collectRenderDisplays($entities, $view_mode) {
        if (empty($entities)) {
            return [];
        }
        // Collect entity type and bundles.
        $entity_type = current($entities)->getEntityTypeId();
        $bundles = [];
        foreach ($entities as $entity) {
            $bundles[$entity->bundle()] = TRUE;
        }
        $bundles = array_keys($bundles);
        // For each bundle, check the existence and status of:
        // - the display for the view mode,
        // - the 'default' display.
        $candidate_ids = [];
        foreach ($bundles as $bundle) {
            if ($view_mode != 'default') {
                $candidate_ids[$bundle][] = $entity_type . '.' . $bundle . '.' . $view_mode;
            }
            $candidate_ids[$bundle][] = $entity_type . '.' . $bundle . '.default';
        }
        $results = \Drupal::entityQuery('entity_view_display')->condition('id', NestedArray::mergeDeepArray($candidate_ids))
            ->condition('status', TRUE)
            ->execute();
        // For each bundle, select the first valid candidate display, if any.
        $load_ids = [];
        foreach ($bundles as $bundle) {
            foreach ($candidate_ids[$bundle] as $candidate_id) {
                if (isset($results[$candidate_id])) {
                    $load_ids[$bundle] = $candidate_id;
                    break;
                }
            }
        }
        // Load the selected displays.
        $storage = \Drupal::entityTypeManager()->getStorage('entity_view_display');
        $displays = $storage->loadMultiple($load_ids);
        $displays_by_bundle = [];
        foreach ($bundles as $bundle) {
            // Use the selected display if any, or create a fresh runtime object.
            if (isset($load_ids[$bundle])) {
                $display = $displays[$load_ids[$bundle]];
            }
            else {
                $display = $storage->create([
                    'targetEntityType' => $entity_type,
                    'bundle' => $bundle,
                    'mode' => $view_mode,
                    'status' => TRUE,
                ]);
            }
            // Let the display know which view mode was originally requested.
            $display->originalMode = $view_mode;
            // Let modules alter the display.
            $display_context = [
                'entity_type' => $entity_type,
                'bundle' => $bundle,
                'view_mode' => $view_mode,
            ];
            \Drupal::moduleHandler()->alter('entity_view_display', $display, $display_context);
            $displays_by_bundle[$bundle] = $display;
        }
        return $displays_by_bundle;
    }
    
    /**
     * Returns the display object used to render an entity.
     *
     * See the collectRenderDisplays() method for details.
     *
     * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
     *   The entity being rendered.
     * @param string $view_mode
     *   The view mode.
     *
     * @return \Drupal\Core\Entity\Display\EntityViewDisplayInterface
     *   The display object that should be used to render the entity.
     *
     * @see \Drupal\Core\Entity\Entity\EntityViewDisplay::collectRenderDisplays()
     */
    public static function collectRenderDisplay(FieldableEntityInterface $entity, $view_mode) {
        $displays = static::collectRenderDisplays([
            $entity,
        ], $view_mode);
        return $displays[$entity->bundle()];
    }
    
    /**
     * {@inheritdoc}
     */
    public function __construct(array $values, $entity_type) {
        $this->pluginManager = \Drupal::service('plugin.manager.field.formatter');
        parent::__construct($values, $entity_type);
    }
    
    /**
     * {@inheritdoc}
     */
    public function postSave(EntityStorageInterface $storage, $update = TRUE) {
        // Reset the render cache for the target entity type.
        parent::postSave($storage, $update);
        if (\Drupal::entityTypeManager()->hasHandler($this->targetEntityType, 'view_builder')) {
            \Drupal::entityTypeManager()->getViewBuilder($this->targetEntityType)
                ->resetCache();
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRenderer($field_name) {
        if (isset($this->plugins[$field_name])) {
            return $this->plugins[$field_name];
        }
        // Instantiate the formatter object from the stored display properties.
        if (($configuration = $this->getComponent($field_name)) && isset($configuration['type']) && ($definition = $this->getFieldDefinition($field_name))) {
            $formatter = $this->pluginManager
                ->getInstance([
                'field_definition' => $definition,
                'view_mode' => $this->originalMode,
                // No need to prepare, defaults have been merged in setComponent().
'prepare' => FALSE,
                'configuration' => $configuration,
            ]);
        }
        else {
            $formatter = NULL;
        }
        // Persist the formatter object.
        $this->plugins[$field_name] = $formatter;
        return $formatter;
    }
    
    /**
     * {@inheritdoc}
     */
    public function build(FieldableEntityInterface $entity) {
        $build = $this->buildMultiple([
            $entity,
        ]);
        return $build[0];
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildMultiple(array $entities) {
        $build_list = [];
        foreach ($entities as $key => $entity) {
            $build_list[$key] = [];
        }
        // Run field formatters.
        foreach ($this->getComponents() as $name => $options) {
            if ($formatter = $this->getRenderer($name)) {
                // Group items across all entities and pass them to the formatter's
                // prepareView() method.
                $grouped_items = [];
                foreach ($entities as $id => $entity) {
                    $items = $entity->get($name);
                    $items->filterEmptyItems();
                    $grouped_items[$id] = $items;
                }
                $formatter->prepareView($grouped_items);
                // Then let the formatter build the output for each entity.
                foreach ($entities as $id => $entity) {
                    $items = $grouped_items[$id];
                    
                    /** @var \Drupal\Core\Access\AccessResultInterface $field_access */
                    $field_access = $items->access('view', NULL, TRUE);
                    // The language of the field values to display is already determined
                    // in the incoming $entity. The formatter should build its output of
                    // those values using:
                    // - the entity language if the entity is translatable,
                    // - the current "content language" otherwise.
                    if ($entity instanceof TranslatableDataInterface && $entity->isTranslatable()) {
                        $view_langcode = $entity->language()
                            ->getId();
                    }
                    else {
                        $view_langcode = NULL;
                    }
                    $build_list[$id][$name] = $field_access->isAllowed() ? $formatter->view($items, $view_langcode) : [];
                    // Apply the field access cacheability metadata to the render array.
                    $this->renderer
                        ->addCacheableDependency($build_list[$id][$name], $field_access);
                }
            }
        }
        foreach ($entities as $id => $entity) {
            // Assign the configured weights.
            foreach ($this->getComponents() as $name => $options) {
                if (isset($build_list[$id][$name]) && !Element::isEmpty($build_list[$id][$name])) {
                    $build_list[$id][$name]['#weight'] = $options['weight'];
                }
            }
            // Let other modules alter the renderable array.
            $context = [
                'entity' => $entity,
                'view_mode' => $this->originalMode,
                'display' => $this,
            ];
            \Drupal::moduleHandler()->alter('entity_display_build', $build_list[$id], $context);
        }
        return $build_list;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getPluginCollections() {
        $configurations = [];
        foreach ($this->getComponents() as $field_name => $configuration) {
            if (!empty($configuration['type']) && ($field_definition = $this->getFieldDefinition($field_name))) {
                $configurations[$configuration['type']] = $configuration + [
                    'field_definition' => $field_definition,
                    'view_mode' => $this->originalMode,
                ];
            }
        }
        return [
            'formatters' => new EntityDisplayPluginCollection($this->pluginManager, $configurations),
        ];
    }

}