REF: implement _ea_wrap_cython_operation

pandas/core/groupby/ops.py

@@ -24,7 +24,7 @@
 from pandas._libs import NaT, iNaT, lib
 import pandas._libs.groupby as libgroupby
 import pandas._libs.reduction as libreduction
-from pandas._typing import F, FrameOrSeries, Label, Shape
+from pandas._typing import ArrayLike, F, FrameOrSeries, Label, Shape
 from pandas.errors import AbstractMethodError
 from pandas.util._decorators import cache_readonly
 
@@ -445,6 +445,68 @@ def _get_cython_func_and_vals(
                 raise
         return func, values
 
+    def _disallow_invalid_ops(self, values: ArrayLike, how: str):
+        """
+        Check if we can do this operation with our cython functions.
+
+        Raises
+        ------
+        NotImplementedError
+            This is either not a valid function for this dtype, or
+            valid but not implemented in cython.
+        """
+        dtype = values.dtype
+
+        if is_categorical_dtype(dtype) or is_sparse(dtype):
+            # categoricals are only 1d, so we
+            #  are not setup for dim transforming
+            raise NotImplementedError(f"{dtype} dtype not supported")
+        elif is_datetime64_any_dtype(dtype):
+            # we raise NotImplemented if this is an invalid operation
+            #  entirely, e.g. adding datetimes
+            if how in ["add", "prod", "cumsum", "cumprod"]:
+                raise NotImplementedError(
+                    f"datetime64 type does not support {how} operations"
+                )
+        elif is_timedelta64_dtype(dtype):
+            if how in ["prod", "cumprod"]:
+                raise NotImplementedError(
+                    f"timedelta64 type does not support {how} operations"
+                )
+
+    def _ea_wrap_cython_operation(
+        self, kind: str, values, how: str, axis: int, min_count: int = -1, **kwargs
+    ) -> Tuple[np.ndarray, Optional[List[str]]]:
+        """
+        If we have an ExtensionArray, unwrap, call _cython_operation, and
+        re-wrap if appropriate.
+        """
+        # TODO: general case implementation overrideable by EAs.
+        orig_values = values
+
+        if is_datetime64tz_dtype(values.dtype) or is_period_dtype(values.dtype):
+            # All of the functions implemented here are ordinal, so we can
+            #  operate on the tz-naive equivalents
+            values = values.view("M8[ns]")
+            res_values, names = self._cython_operation(
+                kind, values, how, axis, min_count, **kwargs
+            )
+            res_values = res_values.astype("i8", copy=False)
+            # FIXME: this is wrong for rank, but not tested.
+            result = type(orig_values)._simple_new(res_values, dtype=orig_values.dtype)
+            return result, names
+
+        elif is_integer_dtype(values.dtype) or is_bool_dtype(values.dtype):
+            # IntegerArray or BooleanArray
+            values = ensure_int_or_float(values)
+            res_values, names = self._cython_operation(
+                kind, values, how, axis, min_count, **kwargs
+            )
+            result = maybe_cast_result(result=res_values, obj=orig_values, how=how)
+            return result, names
+
+        raise NotImplementedError(values.dtype)
+
     def _cython_operation(
         self, kind: str, values, how: str, axis: int, min_count: int = -1, **kwargs
     ) -> Tuple[np.ndarray, Optional[List[str]]]:
@@ -454,8 +516,8 @@ def _cython_operation(
         Names is only useful when dealing with 2D results, like ohlc
         (see self._name_functions).
         """
-        assert kind in ["transform", "aggregate"]
         orig_values = values
+        assert kind in ["transform", "aggregate"]
 
         if values.ndim > 2:
             raise NotImplementedError("number of dimensions is currently limited to 2")
@@ -466,30 +528,12 @@ def _cython_operation(
 
         # can we do this operation with our cython functions
         # if not raise NotImplementedError
+        self._disallow_invalid_ops(values, how)
 
-        # we raise NotImplemented if this is an invalid operation
-        # entirely, e.g. adding datetimes
-
-        # categoricals are only 1d, so we
-        # are not setup for dim transforming
-        if is_categorical_dtype(values.dtype) or is_sparse(values.dtype):
-            raise NotImplementedError(f"{values.dtype} dtype not supported")
-        elif is_datetime64_any_dtype(values.dtype):
-            if how in ["add", "prod", "cumsum", "cumprod"]:
-                raise NotImplementedError(
-                    f"datetime64 type does not support {how} operations"
-                )
-        elif is_timedelta64_dtype(values.dtype):
-            if how in ["prod", "cumprod"]:
-                raise NotImplementedError(
-                    f"timedelta64 type does not support {how} operations"
-                )
-
-        if is_datetime64tz_dtype(values.dtype):
-            # Cast to naive; we'll cast back at the end of the function
-            # TODO: possible need to reshape?
-            # TODO(EA2D):kludge can be avoided when 2D EA is allowed.
-            values = values.view("M8[ns]")
+        if is_extension_array_dtype(values.dtype):
+            return self._ea_wrap_cython_operation(
+                kind, values, how, axis, min_count, **kwargs
+            )
 
         is_datetimelike = needs_i8_conversion(values.dtype)
         is_numeric = is_numeric_dtype(values.dtype)
@@ -573,19 +617,9 @@ def _cython_operation(
         if swapped:
             result = result.swapaxes(0, axis)
 
-        if is_datetime64tz_dtype(orig_values.dtype) or is_period_dtype(
-            orig_values.dtype
-        ):
-            # We need to use the constructors directly for these dtypes
-            # since numpy won't recognize them
-            # https://github.com/pandas-dev/pandas/issues/31471
-            result = type(orig_values)(result.astype(np.int64), dtype=orig_values.dtype)
-        elif is_datetimelike and kind == "aggregate":
+        if is_datetimelike and kind == "aggregate":
             result = result.astype(orig_values.dtype)
 
-        if is_extension_array_dtype(orig_values.dtype):
-            result = maybe_cast_result(result=result, obj=orig_values, how=how)
-
         return result, names
 
     def _aggregate(