Add ValidGPC formencode validator

tailbone/forms/validators.py

@@ -26,8 +26,11 @@ Custom Form Validators
 
 from __future__ import unicode_literals, absolute_import
 
+import re
+
 from rattail.db import model
 from rattail.db.util import validate_email_address, validate_phone_number
+from rattail.gpc import GPC
 
 import formencode as fe
 import formalchemy as fa
@@ -35,6 +38,26 @@ import formalchemy as fa
 from tailbone.db import Session
 
 
+class ValidGPC(fe.validators.FancyValidator):
+    """
+    Validator for fields which should contain GPC value.
+    """
+
+    def _to_python(self, value, state):
+        if value is not None:
+            digits = re.sub(r'\D', '', value)
+            if digits:
+                try:
+                    return GPC(digits)
+                except ValueError as error:
+                    raise fe.Invalid("Invalid UPC: {}".format(error), value, state)
+
+    def _from_python(self, upc, state):
+        if upc is None:
+            return ''
+        return upc.pretty()
+
+
 class ModelValidator(fe.validators.FancyValidator):
     """
     Generic validator for data model reference fields.