feat: request.barmen

counter/middleware.py

@@ -0,0 +1,64 @@
+from typing import TYPE_CHECKING, Callable
+
+from django.db.models import Exists, OuterRef
+from django.http import HttpRequest, HttpResponse
+from django.utils.functional import SimpleLazyObject, empty
+
+from core.models import User
+from counter.models import Permanency
+
+if TYPE_CHECKING:
+    from django.contrib.sessions.backends.base import SessionBase
+
+
+SESSION_BARMEN_KEY = "barmen_ids"
+
+
+def get_cached_barmen(request: HttpRequest) -> set[User]:
+    if not hasattr(request, "_cached_barmen"):
+        session: SessionBase = request.session
+        barmen_ids = session.get(SESSION_BARMEN_KEY, [])
+        if barmen_ids:
+            request._cached_barmen = set(
+                User.objects.filter(
+                    Exists(Permanency.objects.filter(user=OuterRef("pk"), end=None)),
+                    id__in=barmen_ids,
+                )
+            )
+        else:
+            request._cached_barmen = set()
+
+    return request._cached_barmen
+
+
+class BarmenMiddleware:
+    """Inject barmen logged in the current session.
+
+    In a similar fashion as `request.user`, `request.barmen` contains
+    users that are barmen in the current session, and ONLY them ;
+    if a user is logged as a barman on another session,
+    it will not be in `request.barmen`.
+
+    Notes:
+        In case of ended permanence, users will be automatically
+        removed from `request.barmen`.
+        However, in case of newly started permanence, this middleware
+        cannot add new barmen in the session data, so that operation
+        must be explicitly done in the barman login view.
+    """
+
+    def __init__(self, get_response: Callable[[HttpRequest], HttpResponse]):
+        self.get_response = get_response
+
+    def __call__(self, request: HttpRequest):
+        request.barmen = SimpleLazyObject(lambda: get_cached_barmen(request))
+
+        response = self.get_response(request)
+
+        if request.barmen._wrapped is not empty and {
+            b.id for b in request.barmen
+        } != set(request.session.get(SESSION_BARMEN_KEY, [])):
+            # update the session data only if `session.barmen`
+            # has been accessed and modified.
+            request.session[SESSION_BARMEN_KEY] = [b.id for b in request.barmen]
+        return response