Fix #448 -- Add PlaceholderValidator (#465)

* Integrated PlaceholderValidator to MailForm at plugins/sendmail

* Integrated PlaceholderValidator to MailForm and MailSettingsForm

* Typo

src/pretix/base/forms/__init__.py

@@ -6,6 +6,7 @@ from django.utils import six
 from django.utils.crypto import get_random_string
 from hierarkey.forms import HierarkeyForm
 
+from .validators import PlaceholderValidator
 from pretix.base.models import Event
 
 logger = logging.getLogger('pretix.plugins.ticketoutputpdf')

src/pretix/base/forms/validators.py

@@ -0,0 +1,31 @@
+import re
+from django.core.exceptions import ValidationError
+from django.core.validators import BaseValidator
+from django.utils.translation import ugettext_lazy as _
+
+
+class PlaceholderValidator(BaseValidator):
+    """
+    Takes list of allowed placeholders,
+    validates form field by checking for placeholders,
+    which are not presented in taken list.
+    """
+
+    def __init__(self, limit_value):
+        super().__init__(limit_value)
+        self.limit_value = limit_value
+
+    def __call__(self, value):
+        data_placeholders = list(re.findall(r'({[\w\s]*})', value, re.X))
+        invalid_placeholders = []
+        for placeholder in data_placeholders:
+            if placeholder not in self.limit_value:
+                invalid_placeholders.append(placeholder)
+        if invalid_placeholders:
+            raise ValidationError(
+                _('Invalid placeholder(s): %(value)s'),
+                code='invalid',
+                params={'value': ", ".join(invalid_placeholders,)})
+
+    def clean(self, x):
+        return x