EDTF validation constraint

src/Plugin/Field/FieldType/ExtendedDateTimeFormat.php

@@ -14,6 +14,9 @@
  *   description = @Translation("Extended Date Time Format field"),
  *   default_formatter = "edtf_default",
  *   default_widget = "edtf_default",
+ *   constraints = {
+ *     "EDTF" = {},
+ *   },
  * )
  */
 class ExtendedDateTimeFormat extends StringItem {

src/Plugin/Validation/Constraint/EDTF.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Drupal\controlled_access_terms\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * EDTF constraint plugin.
+ *
+ * @Constraint(
+ *   id = "EDTF",
+ *   label = @Translation("EDTF", context = "Validation"),
+ *   type = "string",
+ * )
+ */
+class EDTF extends Constraint {
+
+  /**
+   * Invalid format message template.
+   *
+   * @var string
+   */
+  public $invalid = '%value is not valid EDTF: %verbose';
+
+}

src/Plugin/Validation/Constraint/EDTFValidator.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Drupal\controlled_access_terms\Plugin\Validation\Constraint;
+
+use Drupal\controlled_access_terms\EDTFUtils;
+
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+use Symfony\Component\Validator\Exception\UnexpectedTypeException;
+
+/**
+ * EDTF validation handler.
+ */
+class EDTFValidator extends ConstraintValidator {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validate($value, Constraint $constraint) {
+    if (!$constraint instanceof EDTF) {
+      throw new UnexpectedTypeException($constraint, EDTF::class);
+    }
+    if (NULL === $value) {
+      return;
+    }
+
+    foreach ($value->getValue() as $val) {
+      foreach (EDTFUtils::validate($val, TRUE, TRUE, FALSE) as $error) {
+        $this->context->buildViolation($constraint->invalid)
+          ->setParameter('%value', $val)
+          ->setParameter('%verbose', $error)
+          ->addViolation();
+      }
+    }
+
+  }
+
+}