Add the AppState model

This allows setting application state during run time

calsocial/app_state.py

@@ -0,0 +1,60 @@
+# Calendar.social
+# Copyright (C) 2018  Gergely Polonkai
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+"""Metaclass for storing and accessing app state
+"""
+
+def get_state_base(self, key):
+    """Method to get a key from the state store
+    """
+
+    return self.__get_state__(key)
+
+def set_state_base(self, key, value):
+    """Method to set a key/value in the state store
+    """
+
+    self.__set_state__(key, str(value))
+
+def set_default_base(self, key, value):
+    """Method to set the default value of a key in the state store
+
+    If key is already in the state store, this method is a no-op.
+    """
+
+    self.__set_state_default__(key, str(value))
+
+
+def app_state_base(klass):
+    """Base class creator for AppStateMeta types
+
+    :param klass: the class to extend
+    :type klass: type
+    :returns: a new class extending ``klass``
+    :rtype: type
+    """
+
+    # Construct the meta class based on the metaclass of ``klass``
+    metaclass = type(
+        klass.__name__ + 'BaseMeta',
+        (type(klass),),
+        {
+            '__getitem__': get_state_base,
+            '__setitem__': set_state_base,
+            'setdefault': set_default_base,
+        })
+
+    return metaclass(klass.__name__ + 'Base', (klass,), {'__abstract__': True})