import inspect
from typing import Any, Callable, Coroutine, TypeVar, Union

from typing_extensions import ParamSpec

__all__ = ("Missing", "copy_doc", "maybe_coroutine")

class _Missing:
    def __repr__(self):
        return "<Missing>"

Missing = _Missing()

T = TypeVar("T")

def copy_doc(from_t: T) -> Callable[[T], T]:
    def inner(to_t: T) -> T:
        to_t.__doc__ = from_t.__doc__
        return to_t
    
    return inner

R_T = TypeVar("R_T")
P = ParamSpec("P")

# its impossible to type this function correctly for a couple reasons:
# 1. isawaitable doesnt narrow while keeping typevars - there is an open pr for this (typeshed#5658) but it cant be merged because mypy doesnt support the feature fully
# 2. typeguard doesnt narrow for the negative case which is dumb imo, so `value` would stay being a union even after the if statement (PEP 647 - "The type is not narrowed in the negative case")

async def maybe_coroutine(func: Callable[P, Union[R_T, Coroutine[Any, Any, R_T]]], *args: P.args, **kwargs: P.kwargs) -> R_T:
    value = func(*args, **kwargs)

    if inspect.isawaitable(value):
        value = await value

    return value  # type: ignore