Add-on: refactor job submission in preparation for 'execute' support

Refactor the job submission operator, to make it easier to allow executing
the operator (that is, running in the foreground, blocking execution until
submission is done).

No functional changes.

addon/flamenco/operators.py

@@ -129,30 +129,14 @@ class FLAMENCO_OT_submit_job(FlamencoOpMixin, bpy.types.Operator):
         return job_type is not None
 
     def invoke(self, context: bpy.types.Context, event: bpy.types.Event) -> set[str]:
-        # Before doing anything, make sure the info we cached about the Manager
-        # is up to date. A change in job storage directory on the Manager can
-        # cause nasty error messages when we submit, and it's better to just be
-        # ahead of the curve and refresh first. This also allows for checking
-        # the actual Manager version before submitting.
-        err = self._check_manager(context)
-        if err:
-            self.report({"WARNING"}, err)
+        filepath, ok = self._presubmit_check(context)
+        if not ok:
             return {"CANCELLED"}
 
-        if not context.blend_data.filepath:
-            # The file path needs to be known before the file can be submitted.
-            self.report(
-                {"ERROR"}, "Please save your .blend file before submitting to Flamenco"
-            )
+        is_running = self._submit_files(context, filepath)
+        if not is_running:
             return {"CANCELLED"}
-
-        filepath = self._save_blendfile(context)
-
-        # Check the job with the Manager, to see if it would be accepted.
-        if not self._check_job(context):
-            return {"CANCELLED"}
-
-        return self._submit_files(context, filepath)
+        return {"RUNNING_MODAL"}
 
     def modal(self, context: bpy.types.Context, event: bpy.types.Event) -> set[str]:
         # This function is called for TIMER events to poll the BAT pack thread.
@@ -244,6 +228,39 @@ class FLAMENCO_OT_submit_job(FlamencoOpMixin, bpy.types.Operator):
             return None
         return manager
 
+    def _presubmit_check(self, context: bpy.types.Context) -> tuple[Path, bool]:
+        """Do a pre-submission check, returning whether submission can continue.
+
+        Reports warnings when returning False, so the caller can just abort.
+
+        Returns a tuple (can_submit, filepath_to_submit)
+        """
+
+        # Before doing anything, make sure the info we cached about the Manager
+        # is up to date. A change in job storage directory on the Manager can
+        # cause nasty error messages when we submit, and it's better to just be
+        # ahead of the curve and refresh first. This also allows for checking
+        # the actual Manager version before submitting.
+        err = self._check_manager(context)
+        if err:
+            self.report({"WARNING"}, err)
+            return Path(), False
+
+        if not context.blend_data.filepath:
+            # The file path needs to be known before the file can be submitted.
+            self.report(
+                {"ERROR"}, "Please save your .blend file before submitting to Flamenco"
+            )
+            return Path(), False
+
+        filepath = self._save_blendfile(context)
+
+        # Check the job with the Manager, to see if it would be accepted.
+        if not self._check_job(context):
+            return Path(), False
+
+        return filepath, True
+
     def _save_blendfile(self, context):
         """Save to a different file, specifically for Flamenco.
 
@@ -303,19 +320,22 @@ class FLAMENCO_OT_submit_job(FlamencoOpMixin, bpy.types.Operator):
 
         return filepath
 
-    def _submit_files(self, context: bpy.types.Context, blendfile: Path) -> set[str]:
-        """Ensure that the files are somewhere in the shared storage."""
+    def _submit_files(self, context: bpy.types.Context, blendfile: Path) -> bool:
+        """Ensure that the files are somewhere in the shared storage.
+
+        Returns True if a packing thread has been started, and False otherwise.
+        """
 
         from .bat import interface as bat_interface
 
         if bat_interface.is_packing():
             self.report({"ERROR"}, "Another packing operation is running")
             self._quit(context)
-            return {"CANCELLED"}
+            return False
 
         manager = self._manager_info(context)
         if not manager:
-            return {"CANCELLED"}
+            return False
 
         if manager.shared_storage.shaman_enabled:
             # self.blendfile_on_farm will be set when BAT created the checkout,
@@ -335,13 +355,13 @@ class FLAMENCO_OT_submit_job(FlamencoOpMixin, bpy.types.Operator):
                 self.blendfile_on_farm = self._bat_pack_filesystem(context, blendfile)
             except FileNotFoundError:
                 self._quit(context)
-                return {"CANCELLED"}
+                return False
 
         context.window_manager.modal_handler_add(self)
         wm = context.window_manager
         self.timer = wm.event_timer_add(self.TIMER_PERIOD, window=context.window)
 
-        return {"RUNNING_MODAL"}
+        return True
 
     def _bat_pack_filesystem(
         self, context: bpy.types.Context, blendfile: Path