class EntityFormDisplay

class EntityFormDisplay extends EntityDisplayBase implements EntityFormDisplayInterface {
    
    /**
     * {@inheritdoc}
     */
    protected $displayContext = 'form';
    
    /**
     * Returns the entity_form_display object used to build an entity form.
     *
     * Depending on the configuration of the form mode for the entity bundle, this
     * can be either the display object associated with the form mode, or the
     * 'default' display.
     *
     * This method should only be used internally when rendering an entity form.
     * When assigning suggested display options for a component in a given form
     * mode, EntityDisplayRepositoryInterface::getFormDisplay() should be used
     * instead, in order to avoid inadvertently modifying the output of other form
     * modes that might happen to use the 'default' display too. Those options
     * will then be effectively applied only if the form mode is configured to use
     * them.
     *
     * hook_entity_form_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 $entity
     *   The entity for which the form is being built.
     * @param string $form_mode
     *   The form mode.
     * @param bool $default_fallback
     *   (optional) Whether the default display should be used to initialize the
     *   form display in case the specified display does not exist. Defaults to
     *   TRUE.
     *
     * @return \Drupal\Core\Entity\Display\EntityFormDisplayInterface
     *   The display object that should be used to build the entity form.
     *
     * @see \Drupal\Core\Entity\EntityDisplayRepositoryInterface::getFormDisplay()
     * @see hook_entity_form_display_alter()
     */
    public static function collectRenderDisplay(FieldableEntityInterface $entity, $form_mode, $default_fallback = TRUE) {
        $entity_type = $entity->getEntityTypeId();
        $bundle = $entity->bundle();
        // Allow modules to change the form mode.
        \Drupal::moduleHandler()->alter('entity_form_mode', $form_mode, $entity);
        // Check the existence and status of:
        // - the display for the form mode,
        // - the 'default' display.
        if ($form_mode != 'default') {
            $candidate_ids[] = $entity_type . '.' . $bundle . '.' . $form_mode;
        }
        if ($default_fallback) {
            $candidate_ids[] = $entity_type . '.' . $bundle . '.default';
        }
        $results = \Drupal::entityQuery('entity_form_display')->condition('id', $candidate_ids)
            ->condition('status', TRUE)
            ->execute();
        // Load the first valid candidate display, if any.
        $storage = \Drupal::entityTypeManager()->getStorage('entity_form_display');
        foreach ($candidate_ids as $candidate_id) {
            if (isset($results[$candidate_id])) {
                $display = $storage->load($candidate_id);
                break;
            }
        }
        // Else create a fresh runtime object.
        if (empty($display)) {
            $display = $storage->create([
                'targetEntityType' => $entity_type,
                'bundle' => $bundle,
                'mode' => $default_fallback ? $form_mode : static::CUSTOM_MODE,
                'status' => TRUE,
            ]);
        }
        // Let the display know which form mode was originally requested.
        $display->originalMode = $form_mode;
        // Let modules alter the display.
        $display_context = [
            'entity_type' => $entity_type,
            'bundle' => $bundle,
            'form_mode' => $form_mode,
        ];
        \Drupal::moduleHandler()->alter('entity_form_display', $display, $display_context);
        return $display;
    }
    
    /**
     * {@inheritdoc}
     */
    public function __construct(array $values, $entity_type) {
        $this->pluginManager = \Drupal::service('plugin.manager.field.widget');
        parent::__construct($values, $entity_type);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRenderer($field_name) {
        if (isset($this->plugins[$field_name])) {
            return $this->plugins[$field_name];
        }
        // Instantiate the widget object from the stored display properties.
        if (($configuration = $this->getComponent($field_name)) && isset($configuration['type']) && ($definition = $this->getFieldDefinition($field_name))) {
            $widget = $this->pluginManager
                ->getInstance([
                'field_definition' => $definition,
                'form_mode' => $this->originalMode,
                // No need to prepare, defaults have been merged in setComponent().
'prepare' => FALSE,
                'configuration' => $configuration,
            ]);
        }
        else {
            $widget = NULL;
        }
        // Persist the widget object.
        $this->plugins[$field_name] = $widget;
        return $widget;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(FieldableEntityInterface $entity, array &$form, FormStateInterface $form_state) {
        // Set #parents to 'top-level' by default.
        $form += [
            '#parents' => [],
        ];
        // Let each widget generate the form elements.
        foreach ($this->getComponents() as $name => $options) {
            if ($widget = $this->getRenderer($name)) {
                $items = $entity->get($name);
                $items->filterEmptyItems();
                $form[$name] = $widget->form($items, $form, $form_state);
                $form[$name]['#access'] = $items->access('edit');
                // Assign the correct weight. This duplicates the reordering done in
                // processForm(), but is needed for other forms calling this method
                // directly.
                $form[$name]['#weight'] = $options['weight'];
                // Associate the cache tags for the field definition & field storage
                // definition.
                $field_definition = $this->getFieldDefinition($name);
                $this->renderer
                    ->addCacheableDependency($form[$name], $field_definition);
                $this->renderer
                    ->addCacheableDependency($form[$name], $field_definition->getFieldStorageDefinition());
            }
        }
        // Associate the cache tags for the form display.
        $this->renderer
            ->addCacheableDependency($form, $this);
        // Add a process callback so we can assign weights and hide extra fields.
        $form['#process'][] = [
            $this,
            'processForm',
        ];
    }
    
    /**
     * Process callback: assigns weights and hides extra fields.
     *
     * @see \Drupal\Core\Entity\Entity\EntityFormDisplay::buildForm()
     */
    public function processForm($element, FormStateInterface $form_state, $form) {
        // Assign the weights configured in the form display.
        foreach ($this->getComponents() as $name => $options) {
            if (isset($element[$name])) {
                $element[$name]['#weight'] = $options['weight'];
            }
        }
        // Hide extra fields.
        $extra_fields = \Drupal::service('entity_field.manager')->getExtraFields($this->targetEntityType, $this->bundle);
        $extra_fields = $extra_fields['form'] ?? [];
        foreach ($extra_fields as $extra_field => $info) {
            if (!$this->getComponent($extra_field)) {
                $element[$extra_field]['#access'] = FALSE;
            }
        }
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public function extractFormValues(FieldableEntityInterface $entity, array &$form, FormStateInterface $form_state) {
        $extracted = [];
        foreach ($entity as $name => $items) {
            if ($widget = $this->getRenderer($name)) {
                $widget->extractFormValues($items, $form, $form_state);
                $extracted[$name] = $name;
            }
        }
        return $extracted;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateFormValues(FieldableEntityInterface $entity, array &$form, FormStateInterface $form_state) {
        $violations = $entity->validate();
        $violations->filterByFieldAccess();
        // Flag entity level violations.
        foreach ($violations->getEntityViolations() as $violation) {
            
            /** @var \Symfony\Component\Validator\ConstraintViolationInterface $violation */
            $form_state->setError($form, $violation->getMessage());
        }
        $this->flagWidgetsErrorsFromViolations($violations, $form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function flagWidgetsErrorsFromViolations(EntityConstraintViolationListInterface $violations, array &$form, FormStateInterface $form_state) {
        $entity = $violations->getEntity();
        foreach ($violations->getFieldNames() as $field_name) {
            // Only show violations for fields that actually appear in the form, and
            // let the widget assign the violations to the correct form elements.
            if ($widget = $this->getRenderer($field_name)) {
                $field_violations = $this->movePropertyPathViolationsRelativeToField($field_name, $violations->getByField($field_name));
                $widget->flagErrors($entity->get($field_name), $field_violations, $form, $form_state);
            }
        }
    }
    
    /**
     * Moves the property path to be relative to field level.
     *
     * @param string $field_name
     *   The field name.
     * @param \Symfony\Component\Validator\ConstraintViolationListInterface $violations
     *   The violations.
     *
     * @return \Symfony\Component\Validator\ConstraintViolationList
     *   A new constraint violation list with the changed property path.
     */
    protected function movePropertyPathViolationsRelativeToField($field_name, ConstraintViolationListInterface $violations) {
        $new_violations = new ConstraintViolationList();
        foreach ($violations as $violation) {
            // All the logic below is necessary to change the property path of the
            // violations to be relative to the item list, so like title.0.value gets
            // changed to 0.value. Sadly constraints in Symfony don't have setters so
            // we have to create new objects.
            
            /** @var \Symfony\Component\Validator\ConstraintViolationInterface $violation */
            // Create a new violation object with just a different property path.
            $violation_path = $violation->getPropertyPath();
            $path_parts = explode('.', $violation_path);
            if ($path_parts[0] === $field_name) {
                unset($path_parts[0]);
            }
            $new_path = implode('.', $path_parts);
            $constraint = NULL;
            $cause = NULL;
            $parameters = [];
            $plural = NULL;
            if ($violation instanceof ConstraintViolation) {
                $constraint = $violation->getConstraint();
                $cause = $violation->getCause();
                $parameters = $violation->getParameters();
                $plural = $violation->getPlural();
            }
            $new_violation = new ConstraintViolation($violation->getMessage(), $violation->getMessageTemplate(), $parameters, $violation->getRoot(), $new_path, $violation->getInvalidValue(), $plural, $violation->getCode(), $constraint, $cause);
            $new_violations->add($new_violation);
        }
        return $new_violations;
    }
    
    /**
     * {@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,
                    'form_mode' => $this->mode,
                ];
            }
        }
        return [
            'widgets' => new EntityDisplayPluginCollection($this->pluginManager, $configurations),
        ];
    }

}