feat: advanced catches at payment processing to prevent the payment loss

routes/payments/pally.py

@@ -6,7 +6,11 @@ from fastapi.routing import APIRouter
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from core.deps import get_db
+from db.models.transactions import BalanceTransaction, BalanceTxType
 from external.pally import BillStatus
+from repositories.invoices import InvoiceRepository
+from repositories.users import UserRepository
+from schemas.invoices import InvoiceStatus
 from services.payments import process_subscription_purchase, validate_pally_signature
 
 router = APIRouter(prefix="/payments/pally")
@@ -82,11 +86,69 @@ async def pally_callback(
 
     amount = int(float(BalanceAmount)) if BalanceAmount is not None else int(float(OutSum))
 
+    try:
         await process_subscription_purchase(
             session,
             invoice_id=int(invoice_id_str),
             trs_id=TrsId,
             amount=amount,
         )
+    except Exception:
+        # The payment is confirmed, so never leave the user without the money
+        # if order/subscription provisioning fails.
+        logger.exception(
+            "Subscription provisioning failed for bill %s (TrsId: %s); "
+            "crediting the user's bonus balance",
+            invoice_id_str,
+            TrsId,
+        )
+        await session.rollback()
+
+        invoice_repo = InvoiceRepository(session)
+        invoice = await invoice_repo.get_by_id(int(invoice_id_str))
+        if invoice is None:
+            logger.critical(
+                "Cannot credit fallback balance: bill %s was not found (TrsId: %s)",
+                invoice_id_str,
+                TrsId,
+            )
+            raise
+
+        if invoice.status == InvoiceStatus.PAID:
+            return "OK"
+
+        user = await UserRepository(session).get_user_by_id(invoice.creator_id)
+        if user is None:
+            logger.critical(
+                "Cannot credit fallback balance: user %s was not found " "for bill %s (TrsId: %s)",
+                invoice.creator_id,
+                invoice_id_str,
+                TrsId,
+            )
+            raise
+
+        balance_before = user.balance
+        user.balance += amount
+        invoice.status = InvoiceStatus.PAID
+        session.add(
+            BalanceTransaction(
+                user_id=user.id,
+                amount=amount,
+                tx_type=BalanceTxType.DEPOSIT,
+                balance_before=balance_before,
+                balance_after=user.balance,
+                description=(
+                    f"fallback payment credit for invoice {invoice.id} " f"(TrsId: {TrsId})"
+                ),
+            )
+        )
+        await session.commit()
+        logger.info(
+            "Fallback payment credit processed: user_id=%s, amount=%s, " "invoice_id=%s, TrsId=%s",
+            user.id,
+            amount,
+            invoice.id,
+            TrsId,
+        )
 
     return "OK"