import functools
import warnings
from typing import Callable


def deprecated(reason: str) -> Callable:
    def decorator(func: Callable) -> Callable:
        """This is a decorator which can be used to mark functions
        as deprecated. It will result in a warning being emitted
        when the function is used."""

        @functools.wraps(func)
        def new_func(*args, **kwargs):
            warnings.simplefilter("always", DeprecationWarning)  # turn off filter
            warnings.warn(
                "Call to deprecated function {}. {}".format(func.__name__, reason),
                category=DeprecationWarning,
                stacklevel=2,
            )
            warnings.simplefilter("default", DeprecationWarning)  # reset filter
            return func(*args, **kwargs)

        return new_func

    return decorator