class ModerationStateConstraintValidator

class ModerationStateConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    private $entityTypeManager;
    
    /**
     * The moderation info.
     *
     * @var \Drupal\content_moderation\ModerationInformationInterface
     */
    protected $moderationInformation;
    
    /**
     * The current user.
     *
     * @var \Drupal\Core\Session\AccountInterface
     */
    protected $currentUser;
    
    /**
     * The state transition validation service.
     *
     * @var \Drupal\content_moderation\StateTransitionValidationInterface
     */
    protected $stateTransitionValidation;
    
    /**
     * Creates a new ModerationStateConstraintValidator instance.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\content_moderation\ModerationInformationInterface $moderation_information
     *   The moderation information.
     * @param \Drupal\Core\Session\AccountInterface $current_user
     *   The current user.
     * @param \Drupal\content_moderation\StateTransitionValidationInterface $state_transition_validation
     *   The state transition validation service.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, ModerationInformationInterface $moderation_information, AccountInterface $current_user, StateTransitionValidationInterface $state_transition_validation) {
        $this->entityTypeManager = $entity_type_manager;
        $this->moderationInformation = $moderation_information;
        $this->currentUser = $current_user;
        $this->stateTransitionValidation = $state_transition_validation;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'), $container->get('content_moderation.moderation_information'), $container->get('current_user'), $container->get('content_moderation.state_transition_validation'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function validate($value, Constraint $constraint) : void {
        
        /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
        $entity = $value->getEntity();
        // Ignore entities that are not subject to moderation anyway.
        if (!$this->moderationInformation
            ->isModeratedEntity($entity)) {
            return;
        }
        // If the entity is moderated and the item list is empty, ensure users see
        // the same required message as typical NotNull constraints.
        if ($value->isEmpty()) {
            $this->context
                ->addViolation((new NotNullConstraint())->message);
            return;
        }
        $workflow = $this->moderationInformation
            ->getWorkflowForEntity($entity);
        if (!$workflow->getTypePlugin()
            ->hasState($entity->moderation_state->value)) {
            // If the state we are transitioning to doesn't exist, we can't validate
            // the transitions for this entity further.
            $this->context
                ->addViolation($constraint->invalidStateMessage, [
                '%state' => $entity->moderation_state->value,
                '%workflow' => $workflow->label(),
            ]);
            return;
        }
        $new_state = $workflow->getTypePlugin()
            ->getState($entity->moderation_state->value);
        $original_state = $this->moderationInformation
            ->getOriginalState($entity);
        // If a new state is being set and there is an existing state, validate
        // there is a valid transition between them.
        if (!$original_state->canTransitionTo($new_state->id())) {
            $this->context
                ->addViolation($constraint->message, [
                '%from' => $original_state->label(),
                '%to' => $new_state->label(),
            ]);
        }
        else {
            // If we're sure the transition exists, make sure the user has permission
            // to use it.
            if (!$this->stateTransitionValidation
                ->isTransitionValid($workflow, $original_state, $new_state, $this->currentUser, $entity)) {
                $this->context
                    ->addViolation($constraint->invalidTransitionAccess, [
                    '%original_state' => $original_state->label(),
                    '%new_state' => $new_state->label(),
                ]);
            }
        }
    }

}