Link tasks to their restarts

Closes #1711 (closed)

arkindex/ponos/api.py

@@ -223,7 +223,7 @@ class TaskRestart(ProcessACLMixin, CreateAPIView):
             raise ValidationError(
                 detail="Task's state must be in a final state to be restarted."
             )
-        if len(Task.objects.filter(original_task=task)) > 0:
+        if task.restarts.exists():
             raise ValidationError(
                 detail="This task has already been restarted."
             )
@@ -236,6 +236,10 @@ class TaskRestart(ProcessACLMixin, CreateAPIView):
 
         # Rename the original task
         basename, *_ = copy.slug.rsplit("_old", 1)
+        if copy.original_task_id:
+            basename, *_ = copy.slug.rsplit("_old", 1)
+        else:
+            basename = copy.slug
         latest_task = Task.objects.filter(run=copy.run, slug__startswith=f"{basename}_old").order_by("-created").first()
         if not latest_task:
             # There is no previously restarted task: the original task will have the slug slug_old1