Cds 265 url area selector too small selection (#194)

* handle too small area selection

cads_adaptors/tools/area_selector.py

@@ -7,6 +7,7 @@
 from earthkit.transforms import tools as eka_tools
 
 from cads_adaptors.adaptors import Context
+from cads_adaptors.exceptions import InvalidRequest
 
 
 def incompatible_area_error(
@@ -182,6 +183,17 @@ def area_selector(
 
         ds_area = xr.concat(sub_selections, dim=lon_key)
         context.logger.debug(f"ds_area: {ds_area}")
+
+        # Ensure that there are no length zero dimensions
+        for dim in [lat_key, lon_key]:
+            if len(ds_area[dim]) == 0:
+                message = (
+                    f"Area selection resulted in a dataset with zero length dimension for: {dim}.\n"
+                    "Please ensure that your area selection covers at least one point in the data."
+                )
+                context.add_user_visible_error(message)
+                raise InvalidRequest(message)
+
         return ds_area
 
     else:

tests/test_30_area_selector.py

@@ -5,6 +5,7 @@
 import numpy as np
 import xarray as xr
 
+from cads_adaptors.exceptions import InvalidRequest
 from cads_adaptors.tools.area_selector import (
     area_selector,
     get_dim_slices,
@@ -215,6 +216,14 @@ def test_area_selector_regular_partially_oob_lats(self):
                 np.allclose(result.longitude.values, test_result.longitude.values)
             )
 
+    # Test that InvalidRequest exception raised when a dimension has zero length
+    def test_area_selector_zero_length_dim(self):
+        with tempfile.TemporaryDirectory() as temp_dir:
+            test_file = os.path.join(temp_dir, self.input_file)
+            self.ds.to_netcdf(test_file)
+            with self.assertRaises(InvalidRequest):
+                area_selector(test_file, area=[50.4, -10.6, 50.3, -10.5])
+
 
 if __name__ == "__main__":
     unittest.main()