Features: 1) Add AbstractGateway base class with process_transaction and process_callback methods.

Fixes: 1) Correct gateway status handling logic in `payments/signals.py`.

Extra: 1) Remove redundant condition checks in `payments/signals.py`.

payments/gateways/__init__.py

@@ -1,2 +1,12 @@
 class UnknownGatewayError(Exception):
     pass
+
+
+class AbstractGateway:
+    @staticmethod
+    def process_transaction(transaction):
+        raise NotImplementedError
+
+    @staticmethod
+    def process_callback(transaction):
+        raise NotImplementedError

payments/signals.py

@@ -21,7 +21,8 @@ def process_transaction_changes(instance, created, **_kwargs):
         except Exception as e:  # noqa:
             instance.process = {"status": "NOGATEWAY", "error": str(e)}
     if not created:
-        if "success" in str(instance.process).lower() and "notify" in str(instance.process).lower():
+        status = instance.process.get("status", "").lower()
+        success = instance.process.get("success", False)
+
+        if "success" in status or success:
             balance_deposit_email.delay(instance.uuid)
-        if "fail" in str(instance.process).lower() and "notify" in str(instance.process).lower():
-            pass