feat: statement for supplier and customer

api_v1/views/business/balance/views.py

@@ -34,3 +34,29 @@ class CustomerBalanceView(StockChangeViewMixin, views.APIView):
             }
         )
 
+
+class SupplierBalanceView(StockChangeViewMixin, views.APIView):
+    permission_classes = [IsAuthenticated]
+
+    def get(self, request, supplier_id: int):
+        if not self.check_employee_permission(request):
+            return self.permission_error_response('无权限访问')
+
+        merchant = request.user.employee.merchant
+        try:
+            supplier = basic_models.Supplier.objects.get(id=supplier_id, merchant=merchant)
+        except basic_models.Supplier.DoesNotExist:
+            return self.not_found_response('供应商不存在')
+
+        balance: Decimal = business_services.BalanceService.get_supplier_balance(
+            merchant=merchant,
+            supplier=supplier,
+        )
+        return Response(
+            {
+                'supplier': supplier.id,
+                'supplier_name': supplier.name,
+                'balance': str(balance),
+            }
+        )
+