"""Fire-and-forget background tasks that actually run.

The event loop holds only a WEAK reference to a task, so a bare
``create_task`` with no other holder can be garbage-collected mid-flight — a
write that never errors and never lands (the #2663 GC footgun). This module is
the one place that gets the pattern right: strong references in ``_pending``,
discarded on completion, with failures logged at WARNING instead of vanishing.

``note_usage`` and ``retrieval_telemetry`` predate this module and carry their
own copies with bespoke canary semantics; new fire-and-forget callers use this
instead of writing a fourth copy.
"""
from __future__ import annotations

import asyncio
import logging
from collections.abc import Coroutine

logger = logging.getLogger(__name__)

_pending: set[asyncio.Task] = set()


def spawn(coro: Coroutine, *, site: str) -> None:
    """Schedule ``coro`` fire-and-forget; ``site`` names it in failure logs.

    No running loop (sync context outside the app) closes the coroutine and
    skips — every app path runs on the loop, and blocking would be worse.
    """
    try:
        task = asyncio.get_running_loop().create_task(coro)
    except RuntimeError:
        coro.close()
        logger.debug("background task %s skipped — no running event loop", site)
        return
    _pending.add(task)

    def _done(t: asyncio.Task) -> None:
        _pending.discard(t)
        if not t.cancelled() and t.exception() is not None:
            logger.warning(
                "background task %s failed", site, exc_info=t.exception()
            )

    task.add_done_callback(_done)


def start_periodic(interval_s: float, work, *, label: str) -> asyncio.Task:
    """A forever loop that sleeps ``interval_s`` then awaits ``work()``, logging
    (never raising) when a tick fails — the one shape the hourly/daily
    retention sweeps share (log retention, notification sweep, auth-token
    purge). Sleeps FIRST so startup isn't a sweep; holds a strong reference
    like spawn() so the loop cannot be garbage-collected mid-flight."""
    async def _loop() -> None:
        while True:
            await asyncio.sleep(interval_s)
            try:
                await work()
            except Exception:
                logger.exception("periodic task %s failed", label)

    task = asyncio.get_running_loop().create_task(_loop(), name=f"periodic-{label}")
    _pending.add(task)
    task.add_done_callback(_pending.discard)
    return task


async def drain() -> None:
    """Await everything in flight — for tests that need the writes landed."""
    while _pending:
        await asyncio.gather(*list(_pending), return_exceptions=True)
