import asyncio
import atexit
import functools
import inspect
import threading
from concurrent.futures import Future
from typing import Awaitable, Callable, Concatenate, Generic, Literal, Optional, ParamSpec, TypeVar

P = ParamSpec("P")
R = TypeVar("R")
T = TypeVar("T")


class _BackgroundLoopRunner:
    def __init__(self) -> None:
        self._thread: Optional[threading.Thread] = None
        self._loop: Optional[asyncio.AbstractEventLoop] = None
        self._ready = threading.Event()
        self._lock = threading.Lock()

    def _thread_main(self) -> None:
        loop = asyncio.new_event_loop()
        self._loop = loop
        asyncio.set_event_loop(loop)
        self._ready.set()
        try:
            loop.run_forever()
        finally:
            try:
                pending = asyncio.all_tasks(loop)
                for task in pending:
                    task.cancel()
                if pending:
                    loop.run_until_complete(asyncio.gather(*pending, return_exceptions=True))
                loop.run_until_complete(loop.shutdown_asyncgens())
            finally:
                loop.close()

    def _ensure_started(self) -> None:
        if self._thread is not None and self._loop is not None:
            return

        with self._lock:
            if self._thread is not None and self._loop is not None:
                return

            self._ready.clear()
            t = threading.Thread(target=self._thread_main, name="async_to_sync_loop", daemon=True)
            self._thread = t
            t.start()
            self._ready.wait()

    def run(self, coro: Awaitable[R], *, timeout: Optional[float] = None) -> R:
        self._ensure_started()
        loop = self._loop
        if loop is None:
            raise RuntimeError("Background loop was not initialized")

        fut: Future[R] = asyncio.run_coroutine_threadsafe(coro, loop)
        return fut.result(timeout=timeout)

    def shutdown(self) -> None:
        loop = self._loop
        thread = self._thread
        if loop is None or thread is None:
            return

        loop.call_soon_threadsafe(loop.stop)
        thread.join(timeout=1.0)


_default_runner: Optional[_BackgroundLoopRunner] = None


def _get_default_runner() -> _BackgroundLoopRunner:
    global _default_runner
    if _default_runner is None:
        _default_runner = _BackgroundLoopRunner()
        atexit.register(_default_runner.shutdown)
    return _default_runner


InLoopPolicy = Literal["thread", "raise"]


def sync_wrap(
    fn: Callable[P, Awaitable[R]],
    *,
    in_loop: InLoopPolicy = "thread",
    runner: Optional[_BackgroundLoopRunner] = None,
    timeout: Optional[float] = None,
    use_runner: bool = False,
) -> Callable[P, R]:
    @functools.wraps(fn)
    def wrapper(*args: P.args, **kwargs: P.kwargs) -> R:
        coro = fn(*args, **kwargs)

        if use_runner:
            r = runner or _get_default_runner()
            return r.run(coro, timeout=timeout)

        try:
            asyncio.get_running_loop()
        except RuntimeError:
            return asyncio.run(coro)

        if in_loop == "raise":
            raise RuntimeError(
                "Cannot call this sync wrapper from a running event loop. Use await on the async method instead."
            )

        r = runner or _get_default_runner()
        return r.run(coro, timeout=timeout)

    wrapper.__isabstractmethod__ = False
    return wrapper


class SyncMethod(Generic[T, P, R]):
    __isabstractmethod__ = False

    def __init__(
        self,
        async_method: Callable[Concatenate[T, P], Awaitable[R]],
        *,
        in_loop: InLoopPolicy = "thread",
        runner: Optional[_BackgroundLoopRunner] = None,
        timeout: Optional[float] = None,
        use_runner: bool = False,
        cache: bool = True,
    ):
        self._async_name = async_method.__name__
        self._in_loop = in_loop
        self._runner = runner
        self._timeout = timeout
        self._use_runner = use_runner
        self._cache = cache
        self._attr_name: Optional[str] = None

    def __set_name__(self, owner, name: str) -> None:
        self._attr_name = name

    def __get__(self, obj: Optional[T], objtype=None) -> Callable[P, R]:
        if obj is None:
            return self

        if self._cache and self._attr_name is not None:
            cached = obj.__dict__.get(self._attr_name)
            if cached is not None:
                return cached

        async_fn = getattr(obj, self._async_name)

        sync_fn = sync_wrap(
            async_fn,
            in_loop=self._in_loop,
            runner=self._runner,
            timeout=self._timeout,
            use_runner=self._use_runner,
        )
        sync_fn.__signature__ = inspect.signature(async_fn)
        sync_fn.__isabstractmethod__ = False

        if self._cache and self._attr_name is not None:
            obj.__dict__[self._attr_name] = sync_fn

        return sync_fn


def sync_method_wrapper(
    async_method: Callable[Concatenate[T, P], Awaitable[R]],
    *,
    in_loop: InLoopPolicy = "thread",
    runner: Optional[_BackgroundLoopRunner] = None,
    timeout: Optional[float] = None,
    use_runner: bool = False,
    cache: bool = True,
) -> SyncMethod[T, P, R]:
    return SyncMethod(
        async_method,
        in_loop=in_loop,
        runner=runner,
        timeout=timeout,
        use_runner=use_runner,
        cache=cache,
    )