"""Geo cache flush background task.

Registers an APScheduler job that periodically persists newly resolved IP
geo entries from the in-memory ``_dirty`` set to the ``geo_cache`` table.

After Task 2 removed geo cache writes from GET requests, newly resolved IPs
are only held in the in-memory cache until this task flushes them.  With the
default 60-second interval, at most one minute of new resolution results is
at risk on an unexpected process restart.
"""

from __future__ import annotations

from typing import TYPE_CHECKING, Any

import structlog

from app.services import geo_service

if TYPE_CHECKING:
    from fastapi import FastAPI

log: structlog.stdlib.BoundLogger = structlog.get_logger()

#: How often the flush job fires (seconds).  Configurable tuning constant.
GEO_FLUSH_INTERVAL: int = 60

#: Stable APScheduler job ID — ensures re-registration replaces, not duplicates.
JOB_ID: str = "geo_cache_flush"


async def _run_flush(app: Any) -> None:
    """Flush the geo service dirty set to the application database.

    Reads shared resources from ``app.state`` and delegates to
    :func:`~app.services.geo_service.flush_dirty`.

    Args:
        app: The :class:`fastapi.FastAPI` application instance passed via
            APScheduler ``kwargs``.
    """
    db = app.state.db
    count = await geo_service.flush_dirty(db)
    if count > 0:
        log.debug("geo_cache_flush_ran", flushed=count)


def register(app: FastAPI) -> None:
    """Add (or replace) the geo cache flush job in the application scheduler.

    Must be called after the scheduler has been started (i.e., inside the
    lifespan handler, after ``scheduler.start()``).

    Args:
        app: The :class:`fastapi.FastAPI` application instance whose
            ``app.state.scheduler`` will receive the job.
    """
    app.state.scheduler.add_job(
        _run_flush,
        trigger="interval",
        seconds=GEO_FLUSH_INTERVAL,
        kwargs={"app": app},
        id=JOB_ID,
        replace_existing=True,
    )
    log.info("geo_cache_flush_scheduled", interval_seconds=GEO_FLUSH_INTERVAL)