"""Async utility helpers for bridging sync generators to async FastAPI routes."""

from __future__ import annotations

import asyncio
import threading
from typing import AsyncGenerator, Generator, TypeVar

T = TypeVar("T")

_SENTINEL = object()


async def iter_in_thread(sync_gen: Generator[T, None, None]) -> AsyncGenerator[T, None]:
    """Yield items from a synchronous generator without blocking the event loop.

    Runs the generator in a daemon thread, forwarding items via an asyncio.Queue.
    Use this to wrap blocking LLM streaming generators inside async FastAPI routes.
    """
    loop = asyncio.get_running_loop()
    queue: asyncio.Queue = asyncio.Queue(maxsize=32)

    def _drain() -> None:
        try:
            for item in sync_gen:
                future = asyncio.run_coroutine_threadsafe(queue.put(item), loop)
                future.result()
        finally:
            asyncio.run_coroutine_threadsafe(queue.put(_SENTINEL), loop).result()

    thread = threading.Thread(target=_drain, daemon=True)
    thread.start()

    while True:
        item = await queue.get()
        if item is _SENTINEL:
            break
        yield item  # type: ignore[misc]