PI-2472: Refactor AreaWeightedRegridder

lib/iris/analysis/_area_weighted.py

@@ -61,6 +61,10 @@ def __init__(self, src_grid_cube, target_grid_cube, mdtol=1):
         # current usage of the experimental regrid function.
         self._target_grid_cube_cache = None
 
+        self._regrid_info = eregrid._regrid_area_weighted_rectilinear_src_and_grid__prepare(
+            src_grid_cube, self._target_grid_cube
+        )
+
     @property
     def _target_grid_cube(self):
         if self._target_grid_cube_cache is None:
@@ -97,6 +101,6 @@ def __call__(self, cube):
                 "The given cube is not defined on the same "
                 "source grid as this regridder."
             )
-        return eregrid.regrid_area_weighted_rectilinear_src_and_grid(
-            cube, self._target_grid_cube, mdtol=self._mdtol
+        return eregrid._regrid_area_weighted_rectilinear_src_and_grid__perform(
+            cube, self._regrid_info, mdtol=self._mdtol
         )

lib/iris/tests/unit/analysis/area_weighted/test_AreaWeightedRegridder.py

@@ -42,13 +42,17 @@ def extract_grid(self, cube):
 
     def check_mdtol(self, mdtol=None):
         src_grid, target_grid = self.grids()
-        if mdtol is None:
-            regridder = AreaWeightedRegridder(src_grid, target_grid)
-            mdtol = 1
-        else:
-            regridder = AreaWeightedRegridder(
-                src_grid, target_grid, mdtol=mdtol
-            )
+        with mock.patch(
+            "iris.experimental.regrid."
+            "_regrid_area_weighted_rectilinear_src_and_grid__prepare"
+        ) as prepare:
+            if mdtol is None:
+                regridder = AreaWeightedRegridder(src_grid, target_grid)
+                mdtol = 1
+            else:
+                regridder = AreaWeightedRegridder(
+                    src_grid, target_grid, mdtol=mdtol
+                )
 
         # Make a new cube to regrid with different data so we can
         # distinguish between regridding the original src grid
@@ -58,18 +62,22 @@ def check_mdtol(self, mdtol=None):
 
         with mock.patch(
             "iris.experimental.regrid."
-            "regrid_area_weighted_rectilinear_src_and_grid",
+            "_regrid_area_weighted_rectilinear_src_and_grid__perform",
             return_value=mock.sentinel.result,
-        ) as regrid:
+        ) as perform:
             result = regridder(src)
 
-        self.assertEqual(regrid.call_count, 1)
-        _, args, kwargs = regrid.mock_calls[0]
-
-        self.assertEqual(args[0], src)
+        # Prepare:
+        self.assertEqual(prepare.call_count, 1)
+        _, args, kwargs = prepare.mock_calls[0]
         self.assertEqual(
             self.extract_grid(args[1]), self.extract_grid(target_grid)
         )
+
+        # Perform:
+        self.assertEqual(perform.call_count, 1)
+        _, args, kwargs = perform.mock_calls[0]
+        self.assertEqual(args[0], src)
         self.assertEqual(kwargs, {"mdtol": mdtol})
         self.assertIs(result, mock.sentinel.result)