Add support to update the document indexes from workflow state changes.

Add a new workflow field called internal_name for easier workflow
reference in document index templates.
Generalize the PropertyHelper class.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/common/validators.py

@@ -0,0 +1,32 @@
+from __future__ import unicode_literals
+
+import re
+
+from django.core.validators import RegexValidator
+from django.utils import six
+from django.utils.functional import SimpleLazyObject
+from django.utils.translation import ugettext_lazy as _
+
+# These values, if given to validate(), will trigger the self.required check.
+EMPTY_VALUES = (None, '', [], (), {})
+
+
+def _lazy_re_compile(regex, flags=0):
+    """Lazily compile a regex with flags."""
+    def _compile():
+        # Compile the regex if it was not passed pre-compiled.
+        if isinstance(regex, six.string_types):
+            return re.compile(regex, flags)
+        else:
+            assert not flags, 'flags must be empty if regex is passed pre-compiled'
+            return regex
+    return SimpleLazyObject(_compile)
+
+
+internal_name_re = _lazy_re_compile(r'^[a-zA-Z0-9_]+\Z')
+validate_internal_name = RegexValidator(
+    internal_name_re, _(
+        "Enter a valid 'internal name' consisting of letters, numbers, and "
+        "underscores."
+    ), 'invalid'
+)