# The code here is vendored from Xarray under the terms of the Xarray license reproduced below.

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from collections.abc import Hashable, Mapping
from typing import Literal

ZarrWriteModes = Literal["w", "w-", "a", "a-", "r+", "r"]


def _choose_default_mode(
    *,
    mode: ZarrWriteModes | None,
    append_dim: Hashable | None,
    region: Mapping[str, slice | Literal["auto"]] | Literal["auto"] | None,
) -> ZarrWriteModes:
    if mode is None:
        if append_dim is not None:
            mode = "a"
        elif region is not None:
            mode = "r+"
        else:
            mode = "w-"

    if mode not in ["a", "a-"] and append_dim is not None:
        raise ValueError("cannot set append_dim unless mode='a' or mode=None")

    if mode not in ["a", "a-", "r+"] and region is not None:
        raise ValueError(
            "cannot set region unless mode='a', mode='a-', mode='r+' or mode=None"
        )

    if mode not in ["w", "w-", "a", "a-", "r+"]:
        raise ValueError(
            "The only supported options for mode are 'w', "
            f"'w-', 'a', 'a-', and 'r+', but mode={mode!r}"
        )
    return mode
