Move and rename roles_and_permissions.py

This file does not represent a model, but rather a set of utilities
that are specific to user permissions (vs. service permissions).

app/utils/user_permissions.py

@@ -0,0 +1,52 @@
+from itertools import chain
+
+roles = {
+    'send_messages': ['send_texts', 'send_emails', 'send_letters'],
+    'manage_templates': ['manage_templates'],
+    'manage_service': ['manage_users', 'manage_settings'],
+    'manage_api_keys': ['manage_api_keys'],
+    'view_activity': ['view_activity'],
+    'create_broadcasts': ['create_broadcasts', 'reject_broadcasts', 'cancel_broadcasts'],
+    'approve_broadcasts': ['approve_broadcasts', 'reject_broadcasts', 'cancel_broadcasts'],
+}
+
+all_permissions = set(roles.keys())
+all_database_permissions = set(chain(*roles.values()))
+
+permissions = (
+    ('view_activity', 'See dashboard'),
+    ('send_messages', 'Send messages'),
+    ('manage_templates', 'Add and edit templates'),
+    ('manage_service', 'Manage settings, team and usage'),
+    ('manage_api_keys', 'Manage API integration'),
+)
+
+broadcast_permissions = (
+    ('manage_templates', 'Add and edit templates'),
+    ('create_broadcasts', 'Create new alerts'),
+    ('approve_broadcasts', 'Approve alerts'),
+)
+
+
+def translate_permissions_from_db_to_admin_roles(permissions):
+    """
+    Given a list of database permissions, return a set of roles
+
+    A role is returned if all of its database permissions are in the permission list that is passed in.
+    Any permissions in the list that are not database permissions are also returned.
+    """
+    unknown_database_permissions = {p for p in permissions if p not in all_database_permissions}
+
+    return {
+        admin_role for admin_role, db_role_list in roles.items()
+        if set(db_role_list) <= set(permissions)
+    } | unknown_database_permissions
+
+
+def translate_permissions_from_admin_roles_to_db(permissions):
+    """
+    Given a list of admin roles (ie: checkboxes on a permissions edit page for example), return a set of db permissions
+
+    Looks them up in the roles dict, falling back to just passing through if they're not recognised.
+    """
+    return set(chain.from_iterable(roles.get(permission, [permission]) for permission in permissions))