"""Geo cache cleanup background task.

Registers an APScheduler job that periodically removes stale entries from the
``geo_cache`` table — entries that have not been referenced in the configured
retention period (default: 90 days). This prevents unbounded growth of the
database file and maintains query performance on geo lookups.

When a stale IP is encountered again after purge, it will be re-resolved from
the MaxMind database or ip-api.com (if configured), which is acceptable.

Correlation IDs are propagated through the task using :mod:`app.utils.correlation`
so that task logs can be correlated across runs.
"""

from __future__ import annotations

import uuid
from datetime import UTC, datetime, timedelta
from typing import TYPE_CHECKING

import structlog

from app.repositories import geo_cache_repo
from app.tasks.db import task_db
from app.tasks.timeout_utils import run_with_timeout
from app.utils.correlation import get_correlation_id, reset_correlation_id, set_correlation_id
from app.utils.runtime_state import get_effective_settings

if TYPE_CHECKING:
    from fastapi import FastAPI

    from app.config import Settings

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

#: How long to retain geo cache entries (days). Configurable tuning constant.
GEO_CACHE_RETENTION_DAYS: int = 90

#: How often the cleanup job fires (seconds). Default: once per day.
GEO_CLEANUP_INTERVAL: int = 24 * 60 * 60

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

#: Maximum seconds to allow for geo cache cleanup to complete.
TASK_TIMEOUT_SECONDS: int = 60


async def _run_cleanup_with_resources(
    settings: Settings,
    correlation_id: str | None = None,
) -> None:
    """Delete stale entries from the geo cache.

    Calculates a cutoff timestamp (now - retention period) and removes all
    entries with ``last_seen`` before that time. Logs the operation result.

    Args:
        settings: The resolved application settings used for database access.
        correlation_id: Optional correlation ID for log correlation.
    """
    if correlation_id is None:
        correlation_id = str(uuid.uuid4())

    token = set_correlation_id(correlation_id)
    try:
        await _do_cleanup_with_settings(settings)
    finally:
        reset_correlation_id(token)


async def _do_cleanup_with_settings(settings: Settings) -> None:
    """Inner cleanup logic that runs with correlation context set."""

    async def _do_cleanup() -> None:
        cutoff_dt = datetime.now(UTC) - timedelta(days=GEO_CACHE_RETENTION_DAYS)
        cutoff_iso = cutoff_dt.strftime("%Y-%m-%dT%H:%M:%SZ")

        async with task_db(settings) as db:
            deleted = await geo_cache_repo.delete_stale_entries(db, cutoff_iso)
            await db.commit()

        if deleted > 0:
            log.info(
                "geo_cache_cleanup_ran",
                correlation_id=get_correlation_id(),
                deleted=deleted,
                retention_days=GEO_CACHE_RETENTION_DAYS,
            )
        else:
            log.debug(
                "geo_cache_cleanup_ran",
                correlation_id=get_correlation_id(),
                deleted=deleted,
                retention_days=GEO_CACHE_RETENTION_DAYS,
            )

    await run_with_timeout("geo_cache_cleanup", _do_cleanup(), TASK_TIMEOUT_SECONDS)


async def _run_cleanup(app: FastAPI) -> None:
    """Run cleanup with application settings."""
    await _run_cleanup_with_resources(get_effective_settings(app))


def register(app: FastAPI) -> None:
    """Add (or replace) the geo cache cleanup 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.
    """
    settings = get_effective_settings(app)
    scheduler = getattr(app.state, "scheduler", None)
    if scheduler is None:
        # In tests or standalone usage, scheduler may not be on app.state yet.
        # Use a no-op fallback — the heartbeat won't be registered but no crash.
        log.warning("geo_cache_cleanup_no_scheduler")
        return
    scheduler.add_job(
        _run_cleanup_with_resources,
        trigger="interval",
        seconds=GEO_CLEANUP_INTERVAL,
        kwargs={"settings": settings},
        id=JOB_ID,
        replace_existing=True,
    )
    log.info(
        "geo_cache_cleanup_scheduled",
        interval_seconds=GEO_CLEANUP_INTERVAL,
        retention_days=GEO_CACHE_RETENTION_DAYS,
    )