class TaxonomyTermHierarchyConstraintValidator

class TaxonomyTermHierarchyConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    private $entityTypeManager;
    
    /**
     * Creates a new TaxonomyTermHierarchyConstraintValidator instance.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager) {
        $this->entityTypeManager = $entity_type_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function validate($entity, Constraint $constraint) {
        $term_storage = $this->entityTypeManager
            ->getStorage($entity->getEntityTypeId());
        assert($term_storage instanceof TermStorageInterface);
        // Newly created entities should be able to specify a parent.
        if ($entity && $entity->isNew()) {
            return;
        }
        $is_pending_revision = !$entity->isDefaultRevision();
        $pending_term_ids = $term_storage->getTermIdsWithPendingRevisions();
        $ancestors = $term_storage->loadAllParents($entity->id());
        $ancestor_is_pending_revision = (bool) array_intersect_key($ancestors, array_flip($pending_term_ids));
        $new_parents = array_column($entity->parent
            ->getValue(), 'target_id');
        $original_parents = array_keys($term_storage->loadParents($entity->id())) ?: [
            0,
        ];
        if (($is_pending_revision || $ancestor_is_pending_revision) && $new_parents != $original_parents) {
            $this->context
                ->buildViolation($constraint->message)
                ->atPath('parent')
                ->addViolation();
        }
        $original = $term_storage->loadUnchanged($entity->id());
        if (($is_pending_revision || $ancestor_is_pending_revision) && !$entity->weight
            ->equals($original->weight)) {
            $this->context
                ->buildViolation($constraint->message)
                ->atPath('weight')
                ->addViolation();
        }
    }

}