[ModelicaSystem] update plot() function - include checks

* check if OMCProcessLocal is used
* check for available resultfile

Author: syntron

OMPython/ModelicaSystem.py

@@ -1135,21 +1135,28 @@ def simulate(
     def plot(
             self,
             plotdata: str,
-            resultfile: Optional[str] = None,
+            resultfile: Optional[str | os.PathLike] = None,
     ) -> None:
         """
-        Plot via OMC.
+        Plot a variable using OMC; this will work for local OMC usage only (OMCProcessLocal).
         """
 
-        if resultfile is None:
-            # default result file generated by OM
-            plot_result_file = self.getWorkDirectory() / f"{self._model_name}_res.mat"
-        elif os.path.exists(resultfile):
+        if not isinstance(self._getconn.omc_process, OMCProcessLocal):
+            raise ModelicaSystemError("Plot is using the OMC plot functionality; "
+                                      "thus, it is only working if OMC is running locally!")
+
+        plot_result_file = None
+        if resultfile is not None:
             plot_result_file = pathlib.Path(resultfile)
+        elif self._result_file is not None:
+            plot_result_file = pathlib.Path(self._result_file)
         else:
             ModelicaSystemError("No resultfile available - either run simulate() before plotting "
                                 "or provide a result file!")
 
+        if not plot_result_file.is_file():
+            ModelicaSystemError(f"Provided resultfile {repr(plot_result_file.as_posix())} does not exists!")
+
         expr = f'plot({plotdata}, fileName="{plot_result_file.as_posix()}")'
 
         self.sendExpression(expr=expr)