"""reduction utils"""
import warnings
from typing import Optional


# NB: Keep this file in sync with enums in aten/src/ATen/core/Reduction.h


def get_enum(reduction: str) -> int:
    if reduction == "none":
        ret = 0
    elif reduction == "mean":
        ret = 1
    elif reduction == "elementwise_mean":
        warnings.warn(
            "reduction='elementwise_mean' is deprecated. "
            "Please use reduction='mean' instead."
        )
        ret = 1
    elif reduction == "sum":
        ret = 2
    else:
        ret = -1  # TODO: remove once JIT exceptions support control flow
        raise ValueError(f"{reduction} is not a valid value for reduction")
    return ret


# In order to support previous versions, accept boolean size_average and reduce
# and convert them into the new constants for now


# We use these functions in torch/legacy as well, in which case we'll silence the warning
def legacy_get_string(
    size_average: Optional[bool],
    reduce: Optional[bool],
    emit_warning: bool = True,
) -> str:
    warning = "size_average and reduce args will be deprecated, please use reduction='{}' instead."

    if size_average is None:
        size_average = True
    if reduce is None:
        reduce = True

    if size_average and reduce:
        ret = "mean"
    elif reduce:
        ret = "sum"
    else:
        ret = "none"
    if emit_warning:
        warnings.warn(warning.format(ret))
    return ret


def legacy_get_enum(
    size_average: Optional[bool],
    reduce: Optional[bool],
    emit_warning: bool = True,
) -> int:
    return get_enum(legacy_get_string(size_average, reduce, emit_warning))
