How to extend date picker viewhelper of EXT:powermail? - typo3

Question

I need to add a custom validator to the datepicker field. By default, this field comes without any validators.
I've already made the validator settings visible in the TCA of tx_powermail_domain_model_field and added my custom validator as usual.
Now I need the attributes data-parsley-customXXX and data-parsley-error-message added to the HTML input field which is usually done via the the viewhelper in ValidationDataAttributeViewHelper.php:
https://github.com/einpraegsam/powermail/blob/develop/Classes/ViewHelpers/Validation/ValidationDataAttributeViewHelper.php#L342
https://github.com/einpraegsam/powermail/blob/develop/Classes/ViewHelpers/Validation/ValidationDataAttributeViewHelper.php#L348
This is the code I need to extend:
https://github.com/einpraegsam/powermail/blob/develop/Classes/ViewHelpers/Validation/DatepickerDataAttributeViewHelper.php#L32

Answer 1

I found a solution for my problem. As suggested in the comment it's possible to extend the Viewhelper:
ext_localconf.php:
$GLOBALS['TYPO3_CONF_VARS']['SYS']['Objects'][\In2code\Powermail\ViewHelpers\Validation\DatepickerDataAttributeViewHelper::class] = [
'className' => \Vendor\MyExt\Powermail\ViewHelpers\Validation\DatepickerDataAttributeViewHelper::class
];
myext/Classes/Powermail/ViewHelpers/Validation/DatepickerDataAttributeViewHelper.php
<?php
declare(strict_types=1);
namespace Vendor\MyExt\Powermail\ViewHelpers\Validation;
use In2code\Powermail\Domain\Model\Field;
use In2code\Powermail\Utility\LocalizationUtility;
class DatepickerDataAttributeViewHelper extends \In2code\Powermail\ViewHelpers\Validation\DatepickerDataAttributeViewHelper
{
/**
* Returns Data Attribute Array Datepicker settings (FE + BE)
*
* #return array for data attributes
*/
public function render(): array
{
/** #var Field $field */
$field = $this->arguments['field'];
$additionalAttributes = $this->arguments['additionalAttributes'];
$value = $this->arguments['value'];
$additionalAttributes['data-datepicker-force'] =
$this->settings['misc']['datepicker']['forceJavaScriptDatePicker'];
$additionalAttributes['data-datepicker-settings'] = $this->getDatepickerSettings($field);
$additionalAttributes['data-datepicker-months'] = $this->getMonthNames();
$additionalAttributes['data-datepicker-days'] = $this->getDayNames();
$additionalAttributes['data-datepicker-format'] = $this->getFormat($field);
if ($value) {
$additionalAttributes['data-date-value'] = $value;
}
if ($field->getValidation() && $this->isClientValidationEnabled()) {
$value = 1;
if ($field->getValidationConfiguration()) {
$value = $field->getValidationConfiguration();
}
$additionalAttributes['data-parsley-custom' . $field->getValidation()] = $value;
$additionalAttributes['data-parsley-error-message'] =
LocalizationUtility::translate('validationerror_validation.' . $field->getValidation());
}
$this->addMandatoryAttributes($additionalAttributes, $field);
return $additionalAttributes;
}
}