# Source code for cattrs.preconf.bson

    """Preconfigured converters for bson."""
    from base64 import b85decode, b85encode
    from datetime import datetime
    from typing import Any, Type, TypeVar

    from bson import DEFAULT_CODEC_OPTIONS, CodecOptions, ObjectId, decode, encode

    from cattrs._compat import AbstractSet, is_mapping
    from cattrs.gen import make_mapping_structure_fn

    from ..converters import BaseConverter, Converter
    from . import validate_datetime

    T = TypeVar("T")

    class Base85Bytes(bytes):
        """A subclass to help with binary key encoding/decoding."""

    class BsonConverter(Converter):

        def dumps(
            self,
            obj: Any,
            unstructure_as=None,
            check_keys: bool = False,
            codec_options: CodecOptions = DEFAULT_CODEC_OPTIONS,
        ) -> bytes:
            return encode(
                self.unstructure(obj, unstructure_as=unstructure_as),
                check_keys=check_keys,
                codec_options=codec_options,
            )

        def loads(
            self,
            data: bytes,
            cl: Type[T],
            codec_options: CodecOptions = DEFAULT_CODEC_OPTIONS,
        ) -> T:
            return self.structure(decode(data, codec_options=codec_options), cl)

    def configure_converter(converter: BaseConverter):
        """
        Configure the converter for use with the bson library.

        * sets are serialized as lists
        * byte mapping keys are base85-encoded into strings when unstructuring, and reverse
        * non-string, non-byte mapping keys are coerced into strings when unstructuring
        * a deserialization hook is registered for bson.ObjectId by default
        """

        def gen_unstructure_mapping(cl: Any, unstructure_to=None):
            key_handler = str
            args = getattr(cl, "__args__", None)
            if args:
                if issubclass(args[0], str):
                    key_handler = None
                elif issubclass(args[0], bytes):

                    def key_handler(k):
                        return b85encode(k).decode("utf8")

            return converter.gen_unstructure_mapping(
                cl, unstructure_to=unstructure_to, key_handler=key_handler
            )

        def gen_structure_mapping(cl: Any):
            args = getattr(cl, "__args__", None)
            if args and issubclass(args[0], bytes):
                h = make_mapping_structure_fn(cl, converter, key_type=Base85Bytes)
            else:
                h = make_mapping_structure_fn(cl, converter)
            return h

        converter.register_structure_hook(Base85Bytes, lambda v, _: b85decode(v))
        converter._unstructure_func.register_func_list(
            [(is_mapping, gen_unstructure_mapping, True)]
        )
        converter._structure_func.register_func_list(
            [(is_mapping, gen_structure_mapping, True)]
        )

        converter.register_structure_hook(datetime, validate_datetime)
        converter.register_structure_hook(ObjectId, lambda v, _: ObjectId(v))

    def make_converter(*args, **kwargs) -> BsonConverter:
        kwargs["unstruct_collection_overrides"] = {
            **kwargs.get("unstruct_collection_overrides", {}),
            AbstractSet: list,
        }
        res = BsonConverter(*args, **kwargs)
        configure_converter(res)

        return res