from __future__ import annotations

import datetime
import inspect
from contextlib import asynccontextmanager
from operator import attrgetter
from typing import Any, Callable, Coroutine, Iterable, Literal, TypeVar, Union

import ulid
from aiohttp import ClientSession
from typing_extensions import ParamSpec

__all__ = ("_Missing", "Missing", "copy_doc", "maybe_coroutine", "get", "client_session", "parse_timestamp")

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

    def __bool__(self) -> Literal[False]:
        return False

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")

# it is impossible to type this function correctly as  typeguard does not narrow for the negative case,
# so `value` would stay being a union even after the if statement (PEP 647 - "The type is not narrowed in the negative case")
# see typing#926, typing#930, typing#996

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


class Ulid:
    id: str

    @property
    def created_at(self) -> datetime.datetime:
        return ulid.from_str(self.id).timestamp().datetime

class Object(Ulid):
    """Class to mock objects with an id"""
    def __init__(self, id: str):
        self.id = id

def get(iterable: Iterable[T], **attrs: Any) -> T:
    """A convenience function to help get a value from an iterable with a specific attribute

    Examples
    ---------

    .. code-block:: python
        :emphasize-lines: 3

        from revolt import utils

        channel = utils.get(server.channels, name="General")
        await channel.send("Hello general chat.")

    Parameters
    -----------
    iterable: Iterable
        The values to search though
    **attrs: Any
        The attributes to check

    Returns
    --------
    Any
        The value from the iterable with the met attributes

    Raises
    -------
    LookupError
        Raises when none of the values in the iterable matches the attributes

    """
    converted = [(attrgetter(attr.replace('__', '.')), value) for attr, value in attrs.items()]

    for elem in iterable:
        if all(pred(elem) == value for pred, value in converted):
            return elem

    raise LookupError


@asynccontextmanager
async def client_session():
    """A context manager that creates a new aiohttp.ClientSession() and closes it when exiting the context.

    Examples
    ---------

    .. code-block:: python
        :emphasize-lines: 3

        async def main():
            async with client_session() as session:
                client = revolt.Client(session, "TOKEN")
                await client.start()

        asyncio.run(main())
    """
    session = ClientSession()

    try:
        yield session
    finally:
        await session.close()

def parse_timestamp(timestamp: int | str) -> datetime.datetime:
    if isinstance(timestamp, int):
        return datetime.datetime.fromtimestamp(timestamp / 1000, tz=datetime.timezone.utc)
    else:
        return datetime.datetime.strptime(timestamp, "%Y-%m-%dT%H:%M:%S.%f%z")