added UI configuration for default start-time (#1506)

src/Validator/Constraints/DateTimeFormatValidator.php

@@ -0,0 +1,43 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Validator\Constraints;
+
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+use Symfony\Component\Validator\Exception\UnexpectedTypeException;
+
+class DateTimeFormatValidator extends ConstraintValidator
+{
+    /**
+     * @param string|mixed $value
+     * @param Constraint $constraint
+     */
+    public function validate($value, Constraint $constraint)
+    {
+        if (!($constraint instanceof DateTimeFormat)) {
+            throw new UnexpectedTypeException($constraint, __NAMESPACE__ . '\DateTimeFormat');
+        }
+
+        $valid = true;
+
+        try {
+            $test = new \DateTime($value);
+        } catch (\Exception $ex) {
+            $valid = false;
+        }
+
+        if (false === $valid) {
+            $this->context->buildViolation('The given value is not a valid datetime format.')
+                ->setTranslationDomain('validators')
+                ->setCode(DateTimeFormat::INVALID_FORMAT)
+                ->addViolation();
+        }
+    }
+}