"""
Retention: purge generated export workbooks older than AR_RETENTION_DAYS.

EXPORTS ONLY, by design. Uploaded source files are never auto-deleted — they are the audit
source for every published figure, and re-generating the full workbook re-parses them.
Export files are pure derivatives: anything purged can be regenerated with one click, and
the DB row is kept so the Exports list still shows what was generated and when
(`available: false` once the file is gone).

AR_RETENTION_DAYS=0 keeps everything forever.
"""
from __future__ import annotations

import asyncio
import datetime as dt
import logging
import os

from ..config import RETENTION_DAYS
from ..db import models
from ..db.database import SessionLocal

logger = logging.getLogger(__name__)

_SWEEP_INTERVAL_S = 24 * 3600


def purge_old_exports(retention_days: int | None = None) -> int:
    """Delete export files older than the retention window. Returns files removed."""
    days = RETENTION_DAYS if retention_days is None else retention_days
    if days <= 0:
        return 0
    cutoff = dt.datetime.utcnow() - dt.timedelta(days=days)
    removed = 0
    db = SessionLocal()
    try:
        rows = db.query(models.ExportRecord).filter(
            models.ExportRecord.generated_at < cutoff).all()
        for r in rows:
            if not r.path:
                continue
            try:
                if os.path.exists(r.path):
                    os.remove(r.path)
                    removed += 1
            except OSError:
                logger.warning("retention: could not remove %s", r.path)
        if removed:
            logger.info("retention: removed %d export file(s) older than %d days",
                        removed, days)
    except Exception:  # noqa: BLE001 — a failed sweep must never take the app down
        logger.exception("retention sweep failed")
    finally:
        db.close()
    return removed


async def retention_loop() -> None:
    """Daily sweep, started from the app lifespan. Cancelled cleanly on shutdown."""
    while True:
        await asyncio.to_thread(purge_old_exports)
        await asyncio.sleep(_SWEEP_INTERVAL_S)