UniqueLabelInListConstraintValidator.php

<?php

declare (strict_types=1);
namespace Drupal\ckeditor5\Plugin\Validation\Constraint;

use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;
use Symfony\Component\Validator\Exception\UnexpectedTypeException;

/**
 * Uniquely labeled list item constraint validator.
 *
 * @internal
 */
class UniqueLabelInListConstraintValidator extends ConstraintValidator {
  
  /**
   * {@inheritdoc}
   *
   * @throws \Symfony\Component\Validator\Exception\UnexpectedTypeException
   *   Thrown when the given constraint is not supported by this validator.
   */
  public function validate($list, Constraint $constraint) : void {
    if (!$constraint instanceof UniqueLabelInListConstraint) {
      throw new UnexpectedTypeException($constraint, UniqueLabelInListConstraint::class);
    }
    // This validation constraint supports nullable sequences.
    if (!is_array($list)) {
      return;
    }
    $labels = array_column($list, $constraint->labelKey);
    $label_frequencies = array_count_values($labels);
    foreach ($label_frequencies as $label => $frequency) {
      if ($frequency > 1) {
        $this->context
          ->buildViolation($constraint->message)
          ->setParameter('%label', $label)
          ->addViolation();
      }
    }
  }

}