from __future__ import annotations

import threading
from collections.abc import Awaitable, Callable, Generator
from concurrent.futures import FIRST_COMPLETED, Future, ThreadPoolExecutor, wait
from contextlib import AbstractContextManager, contextmanager
from inspect import isawaitable
from types import TracebackType
from typing import (
    Any,
    AsyncContextManager,
    ContextManager,
    Generic,
    Iterable,
    TypeVar,
    cast,
    overload,
)

from ._core import _eventloop
from ._core._eventloop import get_async_backend, get_cancelled_exc_class, threadlocals
from ._core._synchronization import Event
from ._core._tasks import CancelScope, create_task_group
from .abc._tasks import TaskStatus

T_Retval = TypeVar("T_Retval")
T_co = TypeVar("T_co")


def run(func: Callable[..., Awaitable[T_Retval]], *args: object) -> T_Retval:
    """
    Call a coroutine function from a worker thread.

    :param func: a coroutine function
    :param args: positional arguments for the callable
    :return: the return value of the coroutine function

    """
    try:
        async_backend = threadlocals.current_async_backend
        token = threadlocals.current_token
    except AttributeError:
        raise RuntimeError("This function can only be run from an AnyIO worker thread")

    return async_backend.run_async_from_thread(func, args, token=token)


def run_sync(func: Callable[..., T_Retval], *args: object) -> T_Retval:
    """
    Call a function in the event loop thread from a worker thread.

    :param func: a callable
    :param args: positional arguments for the callable
    :return: the return value of the callable

    """
    try:
        async_backend = threadlocals.current_async_backend
        token = threadlocals.current_token
    except AttributeError:
        raise RuntimeError("This function can only be run from an AnyIO worker thread")

    return async_backend.run_sync_from_thread(func, args, token=token)


class _BlockingAsyncContextManager(Generic[T_co], AbstractContextManager):
    _enter_future: Future
    _exit_future: Future
    _exit_event: Event
    _exit_exc_info: tuple[
        type[BaseException] | None, BaseException | None, TracebackType | None
    ] = (None, None, None)

    def __init__(self, async_cm: AsyncContextManager[T_co], portal: BlockingPortal):
        self._async_cm = async_cm
        self._portal = portal

    async def run_async_cm(self) -> bool | None:
        try:
            self._exit_event = Event()
            value = await self._async_cm.__aenter__()
        except BaseException as exc:
            self._enter_future.set_exception(exc)
            raise
        else:
            self._enter_future.set_result(value)

        try:
            # Wait for the sync context manager to exit.
            # This next statement can raise `get_cancelled_exc_class()` if
            # something went wrong in a task group in this async context
            # manager.
            await self._exit_event.wait()
        finally:
            # In case of cancellation, it could be that we end up here before
            # `_BlockingAsyncContextManager.__exit__` is called, and an
            # `_exit_exc_info` has been set.
            result = await self._async_cm.__aexit__(*self._exit_exc_info)
            return result

    def __enter__(self) -> T_co:
        self._enter_future = Future()
        self._exit_future = self._portal.start_task_soon(self.run_async_cm)
        cm = self._enter_future.result()
        return cast(T_co, cm)

    def __exit__(
        self,
        __exc_type: type[BaseException] | None,
        __exc_value: BaseException | None,
        __traceback: TracebackType | None,
    ) -> bool | None:
        self._exit_exc_info = __exc_type, __exc_value, __traceback
        self._portal.call(self._exit_event.set)
        return self._exit_future.result()


class _BlockingPortalTaskStatus(TaskStatus):
    def __init__(self, future: Future):
        self._future = future

    def started(self, value: object = None) -> None:
        self._future.set_result(value)


class BlockingPortal:
    """An object that lets external threads run code in an asynchronous event loop."""

    def __new__(cls) -> BlockingPortal:
        return get_async_backend().create_blocking_portal()

    def __init__(self) -> None:
        self._event_loop_thread_id: int | None = threading.get_ident()
        self._stop_event = Event()
        self._task_group = create_task_group()
        self._cancelled_exc_class = get_cancelled_exc_class()

    async def __aenter__(self) -> BlockingPortal:
        await self._task_group.__aenter__()
        return self

    async def __aexit__(
        self,
        exc_type: type[BaseException] | None,
        exc_val: BaseException | None,
        exc_tb: TracebackType | None,
    ) -> bool | None:
        await self.stop()
        return await self._task_group.__aexit__(exc_type, exc_val, exc_tb)

    def _check_running(self) -> None:
        if self._event_loop_thread_id is None:
            raise RuntimeError("This portal is not running")
        if self._event_loop_thread_id == threading.get_ident():
            raise RuntimeError(
                "This method cannot be called from the event loop thread"
            )

    async def sleep_until_stopped(self) -> None:
        """Sleep until :meth:`stop` is called."""
        await self._stop_event.wait()

    async def stop(self, cancel_remaining: bool = False) -> None:
        """
        Signal the portal to shut down.

        This marks the portal as no longer accepting new calls and exits from
        :meth:`sleep_until_stopped`.

        :param cancel_remaining: ``True`` to cancel all the remaining tasks, ``False``
            to let them finish before returning

        """
        self._event_loop_thread_id = None
        self._stop_event.set()
        if cancel_remaining:
            self._task_group.cancel_scope.cancel()

    async def _call_func(
        self, func: Callable, args: tuple, kwargs: dict[str, Any], future: Future
    ) -> None:
        def callback(f: Future) -> None:
            if f.cancelled() and self._event_loop_thread_id not in (
                None,
                threading.get_ident(),
            ):
                self.call(scope.cancel)

        try:
            retval = func(*args, **kwargs)
            if isawaitable(retval):
                with CancelScope() as scope:
                    if future.cancelled():
                        scope.cancel()
                    else:
                        future.add_done_callback(callback)

                    retval = await retval
        except self._cancelled_exc_class:
            future.cancel()
            future.set_running_or_notify_cancel()
        except BaseException as exc:
            if not future.cancelled():
                future.set_exception(exc)

            # Let base exceptions fall through
            if not isinstance(exc, Exception):
                raise
        else:
            if not future.cancelled():
                future.set_result(retval)
        finally:
            scope = None  # type: ignore[assignment]

    def _spawn_task_from_thread(
        self,
        func: Callable,
        args: tuple[Any, ...],
        kwargs: dict[str, Any],
        name: object,
        future: Future,
    ) -> None:
        """
        Spawn a new task using the given callable.

        Implementors must ensure that the future is resolved when the task finishes.

        :param func: a callable
        :param args: positional arguments to be passed to the callable
        :param kwargs: keyword arguments to be passed to the callable
        :param name: name of the task (will be coerced to a string if not ``None``)
        :param future: a future that will resolve to the return value of the callable,
            or the exception raised during its execution

        """
        raise NotImplementedError

    @overload
    def call(self, func: Callable[..., Awaitable[T_Retval]], *args: object) -> T_Retval:
        ...

    @overload
    def call(self, func: Callable[..., T_Retval], *args: object) -> T_Retval:
        ...

    def call(
        self,
        func: Callable[..., Awaitable[T_Retval] | T_Retval],
        *args: object,
    ) -> T_Retval:
        """
        Call the given function in the event loop thread.

        If the callable returns a coroutine object, it is awaited on.

        :param func: any callable
        :raises RuntimeError: if the portal is not running or if this method is called
            from within the event loop thread

        """
        return cast(T_Retval, self.start_task_soon(func, *args).result())

    @overload
    def start_task_soon(
        self,
        func: Callable[..., Awaitable[T_Retval]],
        *args: object,
        name: object = None,
    ) -> Future[T_Retval]:
        ...

    @overload
    def start_task_soon(
        self, func: Callable[..., T_Retval], *args: object, name: object = None
    ) -> Future[T_Retval]:
        ...

    def start_task_soon(
        self,
        func: Callable[..., Awaitable[T_Retval] | T_Retval],
        *args: object,
        name: object = None,
    ) -> Future[T_Retval]:
        """
        Start a task in the portal's task group.

        The task will be run inside a cancel scope which can be cancelled by cancelling
        the returned future.

        :param func: the target function
        :param args: positional arguments passed to ``func``
        :param name: name of the task (will be coerced to a string if not ``None``)
        :return: a future that resolves with the return value of the callable if the
            task completes successfully, or with the exception raised in the task
        :raises RuntimeError: if the portal is not running or if this method is called
            from within the event loop thread
        :rtype: concurrent.futures.Future[T_Retval]

        .. versionadded:: 3.0

        """
        self._check_running()
        f: Future = Future()
        self._spawn_task_from_thread(func, args, {}, name, f)
        return f

    def start_task(
        self,
        func: Callable[..., Awaitable[Any]],
        *args: object,
        name: object = None,
    ) -> tuple[Future[Any], Any]:
        """
        Start a task in the portal's task group and wait until it signals for readiness.

        This method works the same way as :meth:`.abc.TaskGroup.start`.

        :param func: the target function
        :param args: positional arguments passed to ``func``
        :param name: name of the task (will be coerced to a string if not ``None``)
        :return: a tuple of (future, task_status_value) where the ``task_status_value``
            is the value passed to ``task_status.started()`` from within the target
            function
        :rtype: tuple[concurrent.futures.Future[Any], Any]

        .. versionadded:: 3.0

        """

        def task_done(future: Future) -> None:
            if not task_status_future.done():
                if future.cancelled():
                    task_status_future.cancel()
                elif future.exception():
                    task_status_future.set_exception(future.exception())
                else:
                    exc = RuntimeError(
                        "Task exited without calling task_status.started()"
                    )
                    task_status_future.set_exception(exc)

        self._check_running()
        task_status_future: Future = Future()
        task_status = _BlockingPortalTaskStatus(task_status_future)
        f: Future = Future()
        f.add_done_callback(task_done)
        self._spawn_task_from_thread(func, args, {"task_status": task_status}, name, f)
        return f, task_status_future.result()

    def wrap_async_context_manager(
        self, cm: AsyncContextManager[T_co]
    ) -> ContextManager[T_co]:
        """
        Wrap an async context manager as a synchronous context manager via this portal.

        Spawns a task that will call both ``__aenter__()`` and ``__aexit__()``, stopping
        in the middle until the synchronous context manager exits.

        :param cm: an asynchronous context manager
        :return: a synchronous context manager

        .. versionadded:: 2.1

        """
        return _BlockingAsyncContextManager(cm, self)


@contextmanager
def start_blocking_portal(
    backend: str = "asyncio", backend_options: dict[str, Any] | None = None
) -> Generator[BlockingPortal, Any, None]:
    """
    Start a new event loop in a new thread and run a blocking portal in its main task.

    The parameters are the same as for :func:`~anyio.run`.

    :param backend: name of the backend
    :param backend_options: backend options
    :return: a context manager that yields a blocking portal

    .. versionchanged:: 3.0
        Usage as a context manager is now required.

    """

    async def run_portal() -> None:
        async with BlockingPortal() as portal_:
            if future.set_running_or_notify_cancel():
                future.set_result(portal_)
                await portal_.sleep_until_stopped()

    future: Future[BlockingPortal] = Future()
    with ThreadPoolExecutor(1) as executor:
        run_future = executor.submit(
            _eventloop.run,
            run_portal,  # type: ignore[arg-type]
            backend=backend,
            backend_options=backend_options,
        )
        try:
            wait(
                cast(Iterable[Future], [run_future, future]),
                return_when=FIRST_COMPLETED,
            )
        except BaseException:
            future.cancel()
            run_future.cancel()
            raise

        if future.done():
            portal = future.result()
            cancel_remaining_tasks = False
            try:
                yield portal
            except BaseException:
                cancel_remaining_tasks = True
                raise
            finally:
                try:
                    portal.call(portal.stop, cancel_remaining_tasks)
                except RuntimeError:
                    pass

        run_future.result()
