from __future__ import annotations

from collections.abc import Callable
from contextlib import AsyncExitStack
from functools import partial
from typing import Any

import attrs
from anyio import CapacityLimiter, to_thread

from .._structures import Job
from ..abc import JobExecutor


@attrs.define(eq=False, kw_only=True)
class ThreadPoolJobExecutor(JobExecutor):
    """
    Executes functions in a thread pool.

    :param max_workers: the maximum number of worker threads to keep
    """

    max_workers: int = 40
    _limiter: CapacityLimiter = attrs.field(init=False)

    async def start(self, exit_stack: AsyncExitStack) -> None:
        self._limiter = CapacityLimiter(self.max_workers)

    async def run_job(self, func: Callable[..., Any], job: Job) -> Any:
        wrapped = partial(func, *job.args, **job.kwargs)
        return await to_thread.run_sync(wrapped, limiter=self._limiter)