class ContentEntityForm

class ContentEntityForm extends EntityForm implements ContentEntityFormInterface {
    
    /**
     * The entity being used by this form.
     *
     * @var \Drupal\Core\Entity\ContentEntityInterface|\Drupal\Core\Entity\RevisionLogInterface
     */
    protected $entity;
    
    /**
     * The entity type bundle info service.
     *
     * @var \Drupal\Core\Entity\EntityTypeBundleInfoInterface
     */
    protected $entityTypeBundleInfo;
    
    /**
     * The time service.
     *
     * @var \Drupal\Component\Datetime\TimeInterface
     */
    protected $time;
    
    /**
     * The entity repository service.
     *
     * @var \Drupal\Core\Entity\EntityRepositoryInterface
     */
    protected $entityRepository;
    
    /**
     * Constructs a ContentEntityForm object.
     *
     * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository
     *   The entity repository service.
     * @param \Drupal\Core\Entity\EntityTypeBundleInfoInterface $entity_type_bundle_info
     *   The entity type bundle service.
     * @param \Drupal\Component\Datetime\TimeInterface $time
     *   The time service.
     */
    public function __construct(EntityRepositoryInterface $entity_repository, EntityTypeBundleInfoInterface $entity_type_bundle_info, TimeInterface $time) {
        $this->entityRepository = $entity_repository;
        $this->entityTypeBundleInfo = $entity_type_bundle_info;
        $this->time = $time;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity.repository'), $container->get('entity_type.bundle.info'), $container->get('datetime.time'));
    }
    
    /**
     * {@inheritdoc}
     */
    protected function prepareEntity() {
        parent::prepareEntity();
        // Hide the current revision log message in UI.
        if ($this->showRevisionUi() && !$this->entity
            ->isNew() && $this->entity instanceof RevisionLogInterface) {
            $this->entity
                ->setRevisionLogMessage(NULL);
        }
    }
    
    /**
     * Returns the bundle entity of the entity, or NULL if there is none.
     *
     * @return \Drupal\Core\Entity\EntityInterface|null
     *   The bundle entity.
     */
    protected function getBundleEntity() {
        if ($bundle_entity_type = $this->entity
            ->getEntityType()
            ->getBundleEntityType()) {
            return $this->entityTypeManager
                ->getStorage($bundle_entity_type)
                ->load($this->entity
                ->bundle());
        }
        return NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function form(array $form, FormStateInterface $form_state) {
        if ($this->showRevisionUi()) {
            // Advanced tab must be the first, because other fields rely on that.
            if (!isset($form['advanced'])) {
                $form['advanced'] = [
                    '#type' => 'vertical_tabs',
                    '#weight' => 99,
                ];
            }
        }
        $form = parent::form($form, $form_state);
        // Content entity forms do not use the parent's #after_build callback
        // because they only need to rebuild the entity in the validation and the
        // submit handler because Field API uses its own #after_build callback for
        // its widgets.
        unset($form['#after_build']);
        $this->getFormDisplay($form_state)
            ->buildForm($this->entity, $form, $form_state);
        // Allow modules to act before and after form language is updated.
        $form['#entity_builders']['update_form_langcode'] = '::updateFormLangcode';
        if ($this->showRevisionUi()) {
            $this->addRevisionableFormFields($form);
        }
        $form['footer'] = [
            '#type' => 'container',
            '#weight' => 99,
            '#attributes' => [
                'class' => [
                    'entity-content-form-footer',
                ],
            ],
            '#optional' => TRUE,
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        parent::submitForm($form, $form_state);
        // Update the changed timestamp of the entity.
        $this->updateChangedTime($this->entity);
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildEntity(array $form, FormStateInterface $form_state) {
        
        /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
        $entity = parent::buildEntity($form, $form_state);
        // Mark the entity as requiring validation.
        $entity->setValidationRequired(!$form_state->getTemporaryValue('entity_validated'));
        // Save as a new revision if requested to do so.
        if ($this->showRevisionUi() && !$form_state->isValueEmpty('revision')) {
            $entity->setNewRevision();
            if ($entity instanceof RevisionLogInterface) {
                // If a new revision is created, save the current user as
                // revision author.
                $entity->setRevisionUserId($this->currentUser()
                    ->id());
                $entity->setRevisionCreationTime($this->time
                    ->getRequestTime());
            }
        }
        return $entity;
    }
    
    /**
     * {@inheritdoc}
     *
     * Button-level validation handlers are highly discouraged for entity forms,
     * as they will prevent entity validation from running. If the entity is going
     * to be saved during the form submission, this method should be manually
     * invoked from the button-level validation handler, otherwise an exception
     * will be thrown.
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        parent::validateForm($form, $form_state);
        
        /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
        $entity = $this->buildEntity($form, $form_state);
        $violations = $entity->validate();
        // Remove violations of inaccessible fields.
        $violations->filterByFieldAccess($this->currentUser());
        // In case a field-level submit button is clicked, for example the 'Add
        // another item' button for multi-value fields or the 'Upload' button for a
        // File or an Image field, make sure that we only keep violations for that
        // specific field.
        $edited_fields = [];
        if ($limit_validation_errors = $form_state->getLimitValidationErrors()) {
            foreach ($limit_validation_errors as $section) {
                $field_name = reset($section);
                if ($entity->hasField($field_name)) {
                    $edited_fields[] = $field_name;
                }
            }
            $edited_fields = array_unique($edited_fields);
        }
        else {
            $edited_fields = $this->getEditedFieldNames($form_state);
        }
        // Remove violations for fields that are not edited.
        $violations->filterByFields(array_diff(array_keys($entity->getFieldDefinitions()), $edited_fields));
        $this->flagViolations($violations, $form, $form_state);
        // The entity was validated.
        $entity->setValidationRequired(FALSE);
        $form_state->setTemporaryValue('entity_validated', TRUE);
        return $entity;
    }
    
    /**
     * Gets the names of all fields edited in the form.
     *
     * If a custom entity form adds some fields to the form (i.e. without using
     * the form display), it needs to add its fields here and override
     * flagViolations() for displaying the violations.
     *
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     *
     * @return string[]
     *   An array of field names.
     */
    protected function getEditedFieldNames(FormStateInterface $form_state) {
        return array_keys($this->getFormDisplay($form_state)
            ->getComponents());
    }
    
    /**
     * Flags violations for the current form.
     *
     * If a custom entity form adds some fields to the form (i.e. without using
     * the form display), it needs to add its fields to array returned by
     * getEditedFieldNames() and overwrite this method in order to show any
     * violations for those fields; e.g.:
     * @code
     * foreach ($violations->getByField('name') as $violation) {
     *   $form_state->setErrorByName('name', $violation->getMessage());
     * }
     * parent::flagViolations($violations, $form, $form_state);
     * @endcode
     *
     * @param \Drupal\Core\Entity\EntityConstraintViolationListInterface $violations
     *   The violations to flag.
     * @param array $form
     *   A nested array of form elements comprising the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     */
    protected function flagViolations(EntityConstraintViolationListInterface $violations, array $form, FormStateInterface $form_state) {
        // Flag entity level violations.
        foreach ($violations->getEntityViolations() as $violation) {
            
            /** @var \Symfony\Component\Validator\ConstraintViolationInterface $violation */
            $form_state->setErrorByName(str_replace('.', '][', $violation->getPropertyPath()), $violation->getMessage());
        }
        // Let the form display flag violations of its fields.
        $this->getFormDisplay($form_state)
            ->flagWidgetsErrorsFromViolations($violations, $form, $form_state);
    }
    
    /**
     * Initializes the form state and the entity before the first form build.
     *
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     */
    protected function init(FormStateInterface $form_state) {
        // Ensure we act on the translation object corresponding to the current form
        // language.
        $this->initFormLangcodes($form_state);
        $langcode = $this->getFormLangcode($form_state);
        $this->entity = $this->entity
            ->hasTranslation($langcode) ? $this->entity
            ->getTranslation($langcode) : $this->entity
            ->addTranslation($langcode);
        $form_display = EntityFormDisplay::collectRenderDisplay($this->entity, $this->getOperation());
        $this->setFormDisplay($form_display, $form_state);
        parent::init($form_state);
    }
    
    /**
     * Initializes form language code values.
     *
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     */
    protected function initFormLangcodes(FormStateInterface $form_state) {
        // Store the entity default language to allow checking whether the form is
        // dealing with the original entity or a translation.
        if (!$form_state->has('entity_default_langcode')) {
            $form_state->set('entity_default_langcode', $this->entity
                ->getUntranslated()
                ->language()
                ->getId());
        }
        // This value might have been explicitly populated to work with a particular
        // entity translation. If not we fall back to the most proper language based
        // on contextual information.
        if (!$form_state->has('langcode')) {
            // Imply a 'view' operation to ensure users edit entities in the same
            // language they are displayed. This allows to keep contextual editing
            // working also for multilingual entities.
            $form_state->set('langcode', $this->entityRepository
                ->getTranslationFromContext($this->entity)
                ->language()
                ->getId());
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormLangcode(FormStateInterface $form_state) {
        $this->initFormLangcodes($form_state);
        return $form_state->get('langcode');
    }
    
    /**
     * {@inheritdoc}
     */
    public function isDefaultFormLangcode(FormStateInterface $form_state) {
        $this->initFormLangcodes($form_state);
        return $form_state->get('langcode') == $form_state->get('entity_default_langcode');
    }
    
    /**
     * {@inheritdoc}
     */
    protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
        // First, extract values from widgets.
        $extracted = $this->getFormDisplay($form_state)
            ->extractFormValues($entity, $form, $form_state);
        // Then extract the values of fields that are not rendered through widgets,
        // by simply copying from top-level form values. This leaves the fields
        // that are not being edited within this form untouched.
        foreach ($form_state->getValues() as $name => $values) {
            if ($entity->hasField($name) && !isset($extracted[$name])) {
                $entity->set($name, $values);
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormDisplay(FormStateInterface $form_state) {
        return $form_state->get('form_display');
    }
    
    /**
     * {@inheritdoc}
     */
    public function setFormDisplay(EntityFormDisplayInterface $form_display, FormStateInterface $form_state) {
        $form_state->set('form_display', $form_display);
        return $this;
    }
    
    /**
     * Updates the form language to reflect any change to the entity language.
     *
     * There are use cases for modules to act both before and after form language
     * being updated, thus the update is performed through an entity builder
     * callback, which allows to support both cases.
     *
     * @param string $entity_type_id
     *   The entity type identifier.
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity updated with the submitted values.
     * @param array $form
     *   The complete form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     *
     * @see \Drupal\Core\Entity\ContentEntityForm::form()
     */
    public function updateFormLangcode($entity_type_id, EntityInterface $entity, array $form, FormStateInterface $form_state) {
        $langcode = $entity->language()
            ->getId();
        $form_state->set('langcode', $langcode);
        // If this is the original entity language, also update the default
        // langcode.
        if ($langcode == $entity->getUntranslated()
            ->language()
            ->getId()) {
            $form_state->set('entity_default_langcode', $langcode);
        }
    }
    
    /**
     * Updates the changed time of the entity.
     *
     * Applies only if the entity implements the EntityChangedInterface.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity updated with the submitted values.
     */
    public function updateChangedTime(EntityInterface $entity) {
        if ($entity instanceof EntityChangedInterface) {
            $entity->setChangedTime($this->time
                ->getRequestTime());
        }
    }
    
    /**
     * Add revision form fields if the entity enabled the UI.
     *
     * @param array $form
     *   An associative array containing the structure of the form.
     */
    protected function addRevisionableFormFields(array &$form) {
        
        /** @var ContentEntityTypeInterface $entity_type */
        $entity_type = $this->entity
            ->getEntityType();
        $new_revision_default = $this->getNewRevisionDefault();
        // Add a log field if the "Create new revision" option is checked, or if the
        // current user has the ability to check that option.
        $form['revision_information'] = [
            '#type' => 'details',
            '#title' => $this->t('Revision information'),
            // Open by default when "Create new revision" is checked.
'#open' => $new_revision_default,
            '#group' => 'advanced',
            '#weight' => 20,
            '#access' => $new_revision_default || $this->entity
                ->get($entity_type->getKey('revision'))
                ->access('update'),
            '#optional' => TRUE,
            '#attributes' => [
                'class' => [
                    'entity-content-form-revision-information',
                ],
            ],
            '#attached' => [
                'library' => [
                    'core/drupal.entity-form',
                ],
            ],
        ];
        $form['revision'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Create new revision'),
            '#default_value' => $new_revision_default,
            '#access' => !$this->entity
                ->isNew() && $this->entity
                ->get($entity_type->getKey('revision'))
                ->access('update'),
            '#group' => 'revision_information',
        ];
        // Get log message field's key from definition.
        $log_message_field = $entity_type->getRevisionMetadataKey('revision_log_message');
        if ($log_message_field && isset($form[$log_message_field])) {
            $form[$log_message_field] += [
                '#group' => 'revision_information',
                '#states' => [
                    'visible' => [
                        ':input[name="revision"]' => [
                            'checked' => TRUE,
                        ],
                    ],
                ],
            ];
        }
    }
    
    /**
     * Should new revisions created on default.
     *
     * @return bool
     *   New revision on default.
     */
    protected function getNewRevisionDefault() {
        $new_revision_default = FALSE;
        $bundle_entity = $this->getBundleEntity();
        if ($bundle_entity instanceof RevisionableEntityBundleInterface) {
            // Always use the default revision setting.
            $new_revision_default = $bundle_entity->shouldCreateNewRevision();
        }
        return $new_revision_default;
    }
    
    /**
     * Checks whether the revision form fields should be added to the form.
     *
     * @return bool
     *   TRUE if the form field should be added, FALSE otherwise.
     */
    protected function showRevisionUi() {
        return $this->entity
            ->getEntityType()
            ->showRevisionUi();
    }

}