add proper ToolConfigurationError if chunk size is too large

src/ctapipe/tools/calculate_pixel_stats.py

@@ -121,6 +121,15 @@ def start(self):
                 instrument=False,
                 pointing=False,
             )[tel_id]
+            # Check if the chunk size does not exceed the table length of the input data
+            if self.stats_calculator.stats_aggregators[
+                self.stats_calculator.stats_aggregator_type.tel[tel_id]
+            ].chunk_size > len(dl1_table):
+                raise ToolConfigurationError(
+                    f"Change --StatisticsAggregator.chunk_size to decrease the chunk size "
+                    f"of the aggregation to at least '{len(dl1_table)}' (table length of the "
+                    f"input data for telescope 'tel_id={tel_id}')."
+                )
             # Check if the input column name is in the table
             if self.input_column_name not in dl1_table.colnames:
                 raise ToolConfigurationError(

src/ctapipe/tools/tests/test_calculate_pixel_stats.py

@@ -100,3 +100,18 @@ def test_tool_config_error(tmp_path, dl1_image_file):
             cwd=tmp_path,
             raises=True,
         )
+    # Check if ToolConfigurationError is raised
+    # when the chunk size is larger than the number of events in the input file
+    with pytest.raises(ToolConfigurationError):
+        run_tool(
+            StatisticsCalculatorTool(),
+            argv=[
+                f"--input_url={dl1_image_file}",
+                f"--output_path={monitoring_file}",
+                "--StatisticsCalculatorTool.allowed_tels=3",
+                "--StatisticsAggregator.chunk_size=2500",
+                "--overwrite",
+            ],
+            cwd=tmp_path,
+            raises=True,
+        )