text: <?php
  
  namespace Drupal\content_moderation\Plugin\Validation\Constraint;
  
  use Drupal\content_moderation\StateTransitionValidationInterface;
  use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
  use Drupal\Core\Entity\EntityTypeManagerInterface;
  use Drupal\content_moderation\ModerationInformationInterface;
  use Drupal\Core\Session\AccountInterface;
  use Drupal\Core\Validation\Plugin\Validation\Constraint\NotNullConstraint;
  use Symfony\Component\DependencyInjection\ContainerInterface;
  use Symfony\Component\Validator\Constraint;
  use Symfony\Component\Validator\ConstraintValidator;
  
  /**
   * Checks if a moderation state transition is valid.
   */
  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) {
      /** @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(),
          ]);
        }
      }
    }
  
  }
  