class ContentTranslationSynchronizedFieldsConstraintValidator

class ContentTranslationSynchronizedFieldsConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * The content translation manager.
     *
     * @var \Drupal\content_translation\ContentTranslationManagerInterface
     */
    protected $contentTranslationManager;
    
    /**
     * The field translation synchronizer.
     *
     * @var \Drupal\content_translation\FieldTranslationSynchronizerInterface
     */
    protected $synchronizer;
    
    /**
     * ContentTranslationSynchronizedFieldsConstraintValidator constructor.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\content_translation\ContentTranslationManagerInterface $content_translation_manager
     *   The content translation manager.
     * @param \Drupal\content_translation\FieldTranslationSynchronizerInterface $synchronizer
     *   The field translation synchronizer.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, ContentTranslationManagerInterface $content_translation_manager, FieldTranslationSynchronizerInterface $synchronizer) {
        $this->entityTypeManager = $entity_type_manager;
        $this->contentTranslationManager = $content_translation_manager;
        $this->synchronizer = $synchronizer;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'), $container->get('content_translation.manager'), $container->get('content_translation.synchronizer'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function validate($value, Constraint $constraint) : void {
        
        /** @var \Drupal\content_translation\Plugin\Validation\Constraint\ContentTranslationSynchronizedFieldsConstraint $constraint */
        
        /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
        $entity = $value;
        if ($entity->isNew() || !$entity->getEntityType()
            ->isRevisionable()) {
            return;
        }
        // When changes to untranslatable fields are configured to affect all
        // revision translations, we always allow changes in default revisions.
        if ($entity->isDefaultRevision() && !$entity->isDefaultTranslationAffectedOnly()) {
            return;
        }
        $entity_type_id = $entity->getEntityTypeId();
        if (!$this->contentTranslationManager
            ->isEnabled($entity_type_id, $entity->bundle())) {
            return;
        }
        $synchronized_properties = $this->getSynchronizedPropertiesByField($entity->getFieldDefinitions());
        if (!$synchronized_properties) {
            return;
        }
        
        /** @var \Drupal\Core\Entity\ContentEntityInterface $original */
        $original = $this->getOriginalEntity($entity);
        $original_translation = $this->getOriginalTranslation($entity, $original);
        if ($this->hasSynchronizedPropertyChanges($entity, $original_translation, $synchronized_properties)) {
            if ($entity->isDefaultTranslationAffectedOnly()) {
                foreach ($entity->getTranslationLanguages(FALSE) as $langcode => $language) {
                    if ($entity->getTranslation($langcode)
                        ->hasTranslationChanges()) {
                        $this->context
                            ->addViolation($constraint->defaultTranslationMessage);
                        break;
                    }
                }
            }
            else {
                $this->context
                    ->addViolation($constraint->defaultRevisionMessage);
            }
        }
    }
    
    /**
     * Checks whether any synchronized property has changes.
     *
     * @param \Drupal\Core\Entity\ContentEntityInterface $entity
     *   The entity being validated.
     * @param \Drupal\Core\Entity\ContentEntityInterface $original
     *   The original unchanged entity.
     * @param string[][] $synchronized_properties
     *   An associative array of arrays of synchronized field properties keyed by
     *   field name.
     *
     * @return bool
     *   TRUE if changes in synchronized properties were detected, FALSE
     *   otherwise.
     */
    protected function hasSynchronizedPropertyChanges(ContentEntityInterface $entity, ContentEntityInterface $original, array $synchronized_properties) {
        foreach ($synchronized_properties as $field_name => $properties) {
            foreach ($properties as $property) {
                $items = $entity->get($field_name)
                    ->getValue();
                $original_items = $original->get($field_name)
                    ->getValue();
                if (count($items) !== count($original_items)) {
                    return TRUE;
                }
                foreach ($items as $delta => $item) {
                    // @todo This loose comparison is not fully reliable. Revisit this
                    //   after https://www.drupal.org/project/drupal/issues/2941092.
                    if ($items[$delta][$property] != $original_items[$delta][$property]) {
                        return TRUE;
                    }
                }
            }
        }
        return FALSE;
    }
    
    /**
     * Returns the original unchanged entity to be used to detect changes.
     *
     * @param \Drupal\Core\Entity\ContentEntityInterface $entity
     *   The entity being changed.
     *
     * @return \Drupal\Core\Entity\ContentEntityInterface
     *   The unchanged entity.
     */
    protected function getOriginalEntity(ContentEntityInterface $entity) {
        if (!isset($entity->original)) {
            
            /** @var \Drupal\Core\Entity\RevisionableStorageInterface $storage */
            $storage = $this->entityTypeManager
                ->getStorage($entity->getEntityTypeId());
            $original = $entity->isDefaultRevision() ? $storage->loadUnchanged($entity->id()) : $storage->loadRevision($entity->getLoadedRevisionId());
        }
        else {
            $original = $entity->original;
        }
        return $original;
    }
    
    /**
     * Returns the original translation.
     *
     * @param \Drupal\Core\Entity\ContentEntityInterface $entity
     *   The entity being validated.
     * @param \Drupal\Core\Entity\ContentEntityInterface $original
     *   The original entity.
     *
     * @return \Drupal\Core\Entity\ContentEntityInterface
     *   The original entity translation object.
     */
    protected function getOriginalTranslation(ContentEntityInterface $entity, ContentEntityInterface $original) {
        // If the language of the default translation is changing, the original
        // translation will be the same as the original entity, but they won't
        // necessarily have the same langcode.
        if ($entity->isDefaultTranslation() && $original->language()
            ->getId() !== $entity->language()
            ->getId()) {
            return $original;
        }
        $langcode = $entity->language()
            ->getId();
        if ($original->hasTranslation($langcode)) {
            $original_langcode = $langcode;
        }
        else {
            $metadata = $this->contentTranslationManager
                ->getTranslationMetadata($entity);
            $original_langcode = $metadata->getSource();
        }
        return $original->getTranslation($original_langcode);
    }
    
    /**
     * Returns the synchronized properties for every specified field.
     *
     * @param \Drupal\Core\Field\FieldDefinitionInterface[] $field_definitions
     *   An array of field definitions.
     *
     * @return string[][]
     *   An associative array of arrays of field property names keyed by field
     *   name.
     */
    public function getSynchronizedPropertiesByField(array $field_definitions) {
        $synchronizer = $this->synchronizer;
        $synchronized_properties = array_filter(array_map(function (FieldDefinitionInterface $field_definition) use ($synchronizer) {
            return $synchronizer->getFieldSynchronizedProperties($field_definition);
        }, $field_definitions));
        return $synchronized_properties;
    }

}