Use JSONModel for user model

Our other models inherit from `JSONModel`, rather than manually doing
lookups of the JSON in the `__init__` method. This commit changes the
user model to work in the same way.

I had to add a new concept (`DEFAULTS`) to account for some properties
not always being present in the (mocked) JSON. In reality it might be
that the API does always return these values. This should be looked at
in future work, to see which defaults can be safely removed. At least
now they:
- do not mean any changes are needed to the existing tests
- are explicitly separated from the attributes that we do expect to
  always be in the JSON response

app/models/__init__.py

@@ -4,10 +4,13 @@ from flask import abort
 class JSONModel():
 
     ALLOWED_PROPERTIES = set()
+    DEFAULTS = dict()
 
     def __init__(self, _dict):
         # in the case of a bad request _dict may be `None`
         self._dict = _dict or {}
+        for attribute, default_value in self.DEFAULTS.items():
+            self._dict[attribute] = self._dict.get(attribute, default_value)
 
     def __bool__(self):
         return self._dict != {}

app/models/user.py

@@ -3,6 +3,7 @@ from flask_login import AnonymousUserMixin, UserMixin, login_user
 from notifications_python_client.errors import HTTPError
 from werkzeug.utils import cached_property
 
+from app.models import JSONModel
 from app.models.organisation import Organisation
 from app.models.roles_and_permissions import (
     all_permissions,
@@ -24,23 +25,36 @@ def _get_org_id_from_view_args():
     return str(request.view_args.get('org_id', '')) or None
 
 
-class User(UserMixin):
-    def __init__(self, fields):
-        self.id = fields.get('id')
-        self.name = fields.get('name')
-        self.email_address = fields.get('email_address')
-        self.mobile_number = fields.get('mobile_number')
-        self.password_changed_at = fields.get('password_changed_at')
-        self._set_permissions(fields.get('permissions', {}))
-        self.auth_type = fields.get('auth_type')
-        self.failed_login_count = fields.get('failed_login_count')
-        self.state = fields.get('state')
-        self.max_failed_login_count = current_app.config["MAX_FAILED_LOGIN_COUNT"]
-        self.logged_in_at = fields.get('logged_in_at')
-        self.platform_admin = fields.get('platform_admin')
-        self.current_session_id = fields.get('current_session_id')
-        self.services = fields.get('services', [])
-        self.organisations = fields.get('organisations', [])
+class User(JSONModel, UserMixin):
+
+    ALLOWED_PROPERTIES = {
+        'id',
+        'name',
+        'email_address',
+        'mobile_number',
+        'password_changed_at',
+        'auth_type',
+        'failed_login_count',
+        'state',
+        'logged_in_at',
+        'platform_admin',
+        'current_session_id',
+        'services',
+        'organisations',
+    }
+
+    DEFAULTS = {
+        'current_session_id': None,
+        'services': [],
+        'organisations': [],
+        'logged_in_at': None,
+        'platform_admin': False,
+    }
+
+    def __init__(self, _dict):
+        super().__init__(_dict)
+        self._set_permissions(_dict.get('permissions', {}))
+        self.max_failed_login_count = current_app.config['MAX_FAILED_LOGIN_COUNT']
 
     @classmethod
     def from_id(cls, user_id):