Features: 1) Add GatewayManager and GatewayQuerySet to handle advanced gateway filtering and usage checks; 2) Integrate GatewayManager with Gateway model for automatic query filtering; 3) Introduce can_be_used query annotation for gateway availability.

Fixes: 1) Default to a usable `Gateway` when processing new transactions if none is specified.

Extra: 1) Add missing import for `GatewayManager` in `payments.models`; 2) Refactor gateway availability logic into the manager and query set for cleaner code organization.

payments/managers.py

@@ -0,0 +1,44 @@
+from django.db.models import BooleanField, Case, F, Manager, Q, QuerySet, Sum, Value, When
+from django.db.models.functions import Coalesce
+from django.utils.timezone import now
+
+
+class GatewayQuerySet(QuerySet):
+    def with_usage_sums(self) -> QuerySet:
+        today = now().date()
+        current_month_start = today.replace(day=1)
+        return self.annotate(
+            daily_sum=Coalesce(Sum("transactions__amount", filter=Q(transactions__created__date=today)), Value(0.0)),
+            monthly_sum=Coalesce(
+                Sum("transactions__amount", filter=Q(transactions__created__gte=current_month_start)), Value(0.0)
+            ),
+        )
+
+    def can_be_used(self) -> QuerySet:
+        qs = self.with_usage_sums()
+        qs = qs.annotate(
+            daily_ok=Case(
+                When(daily_limit=0, then=Value(True)),
+                When(daily_sum__lt=F("daily_limit"), then=Value(True)),
+                default=Value(False),
+                output_field=BooleanField(),
+            ),
+            monthly_ok=Case(
+                When(monthly_limit=0, then=Value(True)),
+                When(monthly_sum__lt=F("monthly_limit"), then=Value(True)),
+                default=Value(False),
+                output_field=BooleanField(),
+            ),
+        )
+        return qs.annotate(
+            can_be_used=Case(
+                When(daily_ok=True, monthly_ok=True, is_active=True, then=Value(True)),
+                default=Value(False),
+                output_field=BooleanField(),
+            )
+        ).order_by("-priority")
+
+
+class GatewayManager(Manager.from_queryset(GatewayQuerySet)):
+    def get_queryset(self) -> QuerySet:
+        return super().get_queryset().can_be_used()

payments/models.py

@@ -20,6 +20,7 @@ from django.utils.translation import gettext_lazy as _
 from core.abstract import NiceModel
 from evibes.utils.misc import create_object
 from payments.gateways import AbstractGateway
+from payments.managers import GatewayManager
 
 
 class Transaction(NiceModel):
@@ -87,6 +88,7 @@ class Balance(NiceModel):
 
 
 class Gateway(NiceModel):
+    objects = GatewayManager()
     name = CharField(max_length=20, null=False, blank=False, verbose_name=_("name"))
     default_currency = CharField(
         max_length=4,
@@ -138,6 +140,9 @@ class Gateway(NiceModel):
 
     @property
     def can_be_used(self) -> bool:
+        if not self.is_active:
+            return False
+
         today = now().date()
         current_month_start = today.replace(day=1)
 

payments/signals.py

@@ -5,7 +5,7 @@ from typing import Any
 from django.db.models.signals import post_save
 from django.dispatch import receiver
 
-from payments.models import Balance, Transaction
+from payments.models import Balance, Transaction, Gateway
 from payments.utils.emailing import balance_deposit_email
 from vibes_auth.models import User
 
@@ -24,7 +24,7 @@ def create_balance_on_user_creation_signal(instance: User, created: bool, **kwar
 def process_transaction_changes(instance: Transaction, created: bool, **kwargs: dict[Any, Any]) -> None:
     if created:
         if not instance.gateway:
-            raise ValueError("gateway is required to process a transaction")
+            instance.gateway = Gateway.objects.can_be_used().first()
         try:
             gateway = instance.gateway.get_integration_class_object()
             gateway.process_transaction(instance)