# Source code for cattr.dispatch

    from functools import lru_cache, singledispatch
    from typing import Any, Callable, List, Tuple, Union

    import attr

    from .errors import StructureHandlerNotFoundError

    @attr.s
    class _DispatchNotFound:
        """A dummy object to help signify a dispatch not found."""

        pass

    class MultiStrategyDispatch:
        """
        MultiStrategyDispatch uses a combination of exact-match dispatch,
        singledispatch, and FunctionDispatch.
        """

        __slots__ = (
            "_direct_dispatch",
            "_function_dispatch",
            "_single_dispatch",
            "_generators",
            "dispatch",
        )

        def __init__(self, fallback_func):
            self._direct_dispatch = {}
            self._function_dispatch = FunctionDispatch()
            self._function_dispatch.register(lambda _: True, fallback_func)
            self._single_dispatch = singledispatch(_DispatchNotFound)
            self.dispatch = lru_cache(maxsize=None)(self._dispatch)

        def _dispatch(self, cl):
            try:
                dispatch = self._single_dispatch.dispatch(cl)
                if dispatch is not _DispatchNotFound:
                    return dispatch
            except Exception:
                pass

            direct_dispatch = self._direct_dispatch.get(cl)
            if direct_dispatch is not None:
                return direct_dispatch

            return self._function_dispatch.dispatch(cl)

        def register_cls_list(self, cls_and_handler, direct: bool = False):
            """register a class to direct or singledispatch"""
            for cls, handler in cls_and_handler:
                if direct:
                    self._direct_dispatch[cls] = handler
                else:
                    self._single_dispatch.register(cls, handler)
                    self.clear_direct()
            self.dispatch.cache_clear()

        def register_func_list(
            self,
            func_and_handler: List[
                Union[
                    Tuple[Callable[[Any], bool], Any],
                    Tuple[Callable[[Any], bool], Any, bool],
                ]
            ],
        ):
            """register a function to determine if the handle
            should be used for the type
            """
            for tup in func_and_handler:
                if len(tup) == 2:
                    func, handler = tup
                    self._function_dispatch.register(func, handler)
                else:
                    func, handler, is_gen = tup
                    self._function_dispatch.register(
                        func, handler, is_generator=is_gen
                    )
            self.clear_direct()
            self.dispatch.cache_clear()

        def clear_direct(self):
            """Clear the direct dispatch."""
            self._direct_dispatch.clear()

        def clear_cache(self):
            """Clear all caches."""
            self._direct_dispatch.clear()
            self.dispatch.cache_clear()

    @attr.s(slots=True)
    class FunctionDispatch:
        """
        FunctionDispatch is similar to functools.singledispatch, but
        instead dispatches based on functions that take the type of the
        first argument in the method, and return True or False.

        objects that help determine dispatch should be instantiated objects.
        """

        _handler_pairs: list = attr.ib(factory=list)

        def register(
            self, can_handle: Callable[[Any], bool], func, is_generator=False
        ):
            self._handler_pairs.insert(0, (can_handle, func, is_generator))

        def dispatch(self, typ):
            """
            returns the appropriate handler, for the object passed.
            """
            for can_handle, handler, is_generator in self._handler_pairs:
                # can handle could raise an exception here
                # such as issubclass being called on an instance.
                # it's easier to just ignore that case.
                try:
                    ch = can_handle(typ)
                except Exception:
                    continue
                if ch:
                    if is_generator:
                        return handler(typ)
                    else:
                        return handler
            raise StructureHandlerNotFoundError(
                f"unable to find handler for {typ}", type_=typ
            )