wcfm-booking-avialability-date-format-validity-check

add_action('after_wcfm_products_manage', function() {
    ?>
    <script>
        jQuery(function($) {
            $( document.body ).on( 'wcfm_form_validate', function(event, elem) {
                let $elem = $(elem);
                let $datePickers = $elem.find('input.wcfm_datepicker.hasDatepicker');
                if($datePickers.length) {
                    $datePickers.each( function() {
                        let $datePicker = $(this);
                        if($datePicker.attr('placeholder')!=='YYYY-MM-DD' || !$datePicker.val()) return;
                        if(!isValidDate($datePicker.val())) {
                            if( $wcfm_is_valid_form )
                            $('#' + $elem.attr('id') + ' .wcfm-message').html( '<span class="wcicon-status-cancelled"></span>Invalid date. Use YYYY-MM-DD format.').addClass('wcfm-error').slideDown();
                            else
                            $('#' + $elem.attr('id') + ' .wcfm-message').append( '<br /><span class="wcicon-status-cancelled"></span>Invalid date. Use YYYY-MM-DD format.' );

                            $wcfm_is_valid_form = false;
                            $datePicker.removeClass('wcfm_validation_success').addClass('wcfm_validation_failed');
                            return;
                        }
                    });
                }
            });
            function isValidDate(dateString) {
                const dateFormatRegex = /^\d{4}-\d{2}-\d{2}$/;
                if (!dateFormatRegex.test(dateString)) {
                    return false;
                }

                const parts = dateString.split("-");
                const year = parseInt(parts[0], 10);
                const month = parseInt(parts[1], 10);
                const day = parseInt(parts[2], 10);

                const date = new Date(year, month - 1, day);

                return !isNaN(date.getTime()) &&
                    date.getFullYear() === year &&
                    date.getMonth() === month - 1 &&
                    date.getDate() === day;
            }
        });
    </script>
    <?php
});