Add rattail provider for NationBuilder integration

and use it to generate NB URLs

rattail_nationbuilder/app.py

@@ -0,0 +1,56 @@
+# -*- coding: utf-8; -*-
+################################################################################
+#
+#  Rattail -- Retail Software Framework
+#  Copyright © 2010-2023 Lance Edgar
+#
+#  This file is part of Rattail.
+#
+#  Rattail is free software: you can redistribute it and/or modify it under the
+#  terms of the GNU General Public License as published by the Free Software
+#  Foundation, either version 3 of the License, or (at your option) any later
+#  version.
+#
+#  Rattail is distributed in the hope that it will be useful, but WITHOUT ANY
+#  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+#  FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+#  details.
+#
+#  You should have received a copy of the GNU General Public License along with
+#  Rattail.  If not, see <http://www.gnu.org/licenses/>.
+#
+################################################################################
+"""
+App Handler supplement
+"""
+
+from rattail.app import RattailProvider, GenericHandler
+
+
+class NationBuilderProvider(RattailProvider):
+    """
+    App provider for NationBuilder integration.
+    """
+
+    def get_nationbuilder_handler(self, **kwargs):
+        if 'nationbuilder' not in self.handlers:
+            spec = self.config.get('rattail', 'nationbuilder.handler',
+                                   default='rattail_nationbuilder.app:NationBuilderHandler')
+            factory = self.load_object(spec)
+            self.handlers['nationbuilder'] = factory(self.config, **kwargs)
+        return self.handlers['nationbuilder']
+
+
+class NationBuilderHandler(GenericHandler):
+    """
+    Handler for NationBuilder integration.
+    """
+
+    def get_url(self, require=False, **kwargs):
+        """
+        Returns the base URL for the NationBuilder web app.
+        """
+        getter = self.config.require if require else self.config.get
+        url = getter('nationbuilder', 'url')
+        if url:
+            return url.rstrip('/')

rattail_nationbuilder/nationbuilder/util.py

@@ -24,8 +24,14 @@
 NationBuilder utils
 """
 
+import warnings
+
 
 def get_nationbuilder_url(config):
-    url = config.get('nationbuilder', 'url')
-    if url:
-        return url.rstrip('/')
+    warnings.warn("get_nationbuilder_url() function is deprecated; "
+                  "please use nationbuilder_handler.get_url() instead",
+                  DeprecationWarning, stacklevel=2)
+
+    app = config.get_app()
+    nationbuilder = app.get_nationbuilder_handler()
+    return nationbuilder.get_url()