DateTimeFormatConstraintValidator.php

<?php

namespace Drupal\datetime\Plugin\Validation\Constraint;

use Drupal\Component\Datetime\DateTimePlus;
use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
use Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface;
use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;

/**
 * Constraint validator for DateTime items to ensure the format is correct.
 */
class DateTimeFormatConstraintValidator extends ConstraintValidator {
    
    /**
     * {@inheritdoc}
     */
    public function validate($item, Constraint $constraint) {
        
        /* @var $item \Drupal\datetime\Plugin\Field\FieldType\DateTimeItem */
        if (isset($item)) {
            $value = $item->getValue()['value'];
            if (!is_string($value)) {
                $this->context
                    ->addViolation($constraint->badType);
            }
            else {
                $datetime_type = $item->getFieldDefinition()
                    ->getSetting('datetime_type');
                $format = $datetime_type === DateTimeItem::DATETIME_TYPE_DATE ? DateTimeItemInterface::DATE_STORAGE_FORMAT : DateTimeItemInterface::DATETIME_STORAGE_FORMAT;
                $date = NULL;
                try {
                    $date = DateTimePlus::createFromFormat($format, $value, new \DateTimeZone(DateTimeItemInterface::STORAGE_TIMEZONE));
                } catch (\InvalidArgumentException $e) {
                    $this->context
                        ->addViolation($constraint->badFormat, [
                        '@value' => $value,
                        '@format' => $format,
                    ]);
                    return;
                } catch (\UnexpectedValueException $e) {
                    $this->context
                        ->addViolation($constraint->badValue, [
                        '@value' => $value,
                        '@format' => $format,
                    ]);
                    return;
                }
                if ($date === NULL || $date->hasErrors()) {
                    $this->context
                        ->addViolation($constraint->badFormat, [
                        '@value' => $value,
                        '@format' => $format,
                    ]);
                }
            }
        }
    }

}