From 18e6e6dcdab0e3e41a233cb4d9dc626f99bb0644 Mon Sep 17 00:00:00 2001
From: Mainak Kundu <mainak.kundu@ansys.com>
Date: Mon, 2 Dec 2024 22:54:40 -0500
Subject: [PATCH] feat: optional last

---
 doc/source/user_guide/events.rst              |  6 ++---
 .../streaming_services/events_streaming.py    | 25 +++++++++++--------
 tests/test_events_manager.py                  | 13 +++++++++-
 3 files changed, 29 insertions(+), 15 deletions(-)

diff --git a/doc/source/user_guide/events.rst b/doc/source/user_guide/events.rst
index a8afb9b835d..1bd18e53a0b 100644
--- a/doc/source/user_guide/events.rst
+++ b/doc/source/user_guide/events.rst
@@ -25,10 +25,10 @@ The following code triggers a callback at the end of every iteration.
   >>>
   >>> callback_id = solver.events.register_callback(SolverEvent.ITERATION_ENDED, on_iteration_ended)
 
-The general signature of the callback function is ``cb(<optional arguments>, session, event_info)``, where ``session`` is the session instance
+The general signature of the callback function is ``cb(session, event_info, <additional arguments>)``, where ``session`` is the session instance
 and ``event_info`` instance holds information about the event. The event information classes for each event are documented in the
 API reference of the :obj:`~ansys.fluent.core.streaming_services.events_streaming` module. See the callback function
-``on_case_loaded_with_args()`` in the below examples for an example of how to pass optional arguments to the callback
+``on_case_loaded_with_args()`` in the below examples for an example of how to pass additional arguments to the callback
 function.
 
 
@@ -74,7 +74,7 @@ Examples
   >>> def on_case_loaded(session, event_info: CaseLoadedEventInfo):
   >>>     print("Case loaded. Index = ", event_info.index)
   >>>
-  >>> def on_case_loaded_with_args(x, y, session, event_info: CaseLoadedEventInfo):
+  >>> def on_case_loaded_with_args(session, event_info: CaseLoadedEventInfo, x, y):
   >>>     print(f"Case loaded with {x}, {y}. Index = ", event_info.index)
   >>>
   >>> callback = meshing.events.register_callback(MeshingEvent.CASE_LOADED, on_case_loaded)
diff --git a/src/ansys/fluent/core/streaming_services/events_streaming.py b/src/ansys/fluent/core/streaming_services/events_streaming.py
index b5ce2637e77..0c48c15511f 100644
--- a/src/ansys/fluent/core/streaming_services/events_streaming.py
+++ b/src/ansys/fluent/core/streaming_services/events_streaming.py
@@ -442,23 +442,26 @@ def _process_streaming(
 
     @staticmethod
     def _make_callback_to_call(callback: Callable, args, kwargs):
-        old_style = "session_id" in inspect.signature(callback).parameters
-        if old_style:
+        params = inspect.signature(callback).parameters
+        if "session_id" in params:
             warnings.warn(
                 "Update event callback function signatures"
                 " substituting 'session' for 'session_id'.",
                 PyFluentDeprecationWarning,
             )
-        fn = partial(callback, *args, **kwargs)
-        return (
-            (
-                lambda session, event_info: fn(
-                    session_id=session.id, event_info=event_info
-                )
+            return lambda session, event_info: callback(
+                *args, session_id=session.id, event_info=event_info, **kwargs
+            )
+        else:
+            positional_args = [
+                p
+                for p in params
+                if p not in kwargs and p not in ("session", "event_info")
+            ]
+            kwargs.update(dict(zip(positional_args, args)))
+            return lambda session, event_info: callback(
+                session=session, event_info=event_info, **kwargs
             )
-            if old_style
-            else fn
-        )
 
     def register_callback(
         self,
diff --git a/tests/test_events_manager.py b/tests/test_events_manager.py
index 925ed39de3e..fea1b35b067 100644
--- a/tests/test_events_manager.py
+++ b/tests/test_events_manager.py
@@ -28,7 +28,12 @@ def on_case_loaded(session, event_info):
 
     on_case_loaded.loaded = False
 
-    def on_case_loaded_with_args(x, y, session, event_info):
+    def on_case_loaded_with_args_optional_first(x, y, session, event_info):
+        on_case_loaded_with_args_optional_first.state = dict(x=x, y=y)
+
+    on_case_loaded_with_args_optional_first.state = None
+
+    def on_case_loaded_with_args(session, event_info, x, y):
         on_case_loaded_with_args.state = dict(x=x, y=y)
 
     on_case_loaded_with_args.state = None
@@ -43,6 +48,10 @@ def on_case_loaded_with_args(x, y, session, event_info):
 
     solver.events.register_callback(SolverEvent.CASE_LOADED, on_case_loaded)
 
+    solver.events.register_callback(
+        SolverEvent.CASE_LOADED, on_case_loaded_with_args_optional_first, 12, y=42
+    )
+
     solver.events.register_callback(
         SolverEvent.CASE_LOADED, on_case_loaded_with_args, 12, y=42
     )
@@ -54,6 +63,7 @@ def on_case_loaded_with_args(x, y, session, event_info):
     assert not on_case_loaded_old.loaded
     assert not on_case_loaded.loaded
     assert not on_case_loaded_old_with_args.state
+    assert not on_case_loaded_with_args_optional_first.state
     assert not on_case_loaded_with_args.state
 
     try:
@@ -64,6 +74,7 @@ def on_case_loaded_with_args(x, y, session, event_info):
     assert on_case_loaded_old.loaded
     assert on_case_loaded.loaded
     assert on_case_loaded_old_with_args.state == dict(x=12, y=42)
+    assert on_case_loaded_with_args_optional_first.state == dict(x=12, y=42)
     assert on_case_loaded_with_args.state == dict(x=12, y=42)