"""Periodic maintenance: recover stuck import tasks, garbage-collect old finished tasks."""

import logging
from datetime import UTC, datetime, timedelta

from PIL import Image
from sqlalchemy import create_engine, delete, select, update
from sqlalchemy.orm import sessionmaker

from ..celery_app import celery
from ..config import get_config
from ..models import ImageRecord, ImportTask
from ..utils.phash import compute_phash

log = logging.getLogger(__name__)

STUCK_THRESHOLD_MINUTES = 30
OLD_TASK_DAYS = 7
PHASH_PAGE = 500


def _sync_session_factory():
    cfg = get_config()
    engine = create_engine(cfg.database_url_sync, future=True, pool_pre_ping=True)
    return sessionmaker(engine, expire_on_commit=False)


@celery.task(name="backend.app.tasks.maintenance.recover_interrupted_tasks")
def recover_interrupted_tasks() -> int:
    """Find ImportTask rows stuck in 'processing' for >30 min and re-queue them.

    Why 30 min: large videos can legitimately take many minutes to import;
    30 is a safe gate that catches actual crashes (which leave the row stuck
    forever) without resetting slow-but-still-running jobs.
    """
    SessionLocal = _sync_session_factory()
    cutoff = datetime.now(UTC) - timedelta(minutes=STUCK_THRESHOLD_MINUTES)
    with SessionLocal() as session:
        stuck_ids = session.execute(
            select(ImportTask.id)
            .where(ImportTask.status == "processing")
            .where(ImportTask.started_at < cutoff)
        ).scalars().all()

        if not stuck_ids:
            return 0

        session.execute(
            update(ImportTask)
            .where(ImportTask.id.in_(stuck_ids))
            .values(status="queued", started_at=None, error="recovered from stuck state")
        )
        session.commit()

        from .import_file import import_media_file
        for tid in stuck_ids:
            import_media_file.delay(tid)

        return len(stuck_ids)


@celery.task(name="backend.app.tasks.maintenance.cleanup_old_tasks")
def cleanup_old_tasks() -> int:
    """Delete completed/skipped/failed ImportTask rows older than 7 days.

    Why 7 days: long enough to debug an issue an operator only notices days
    later; short enough that the task table stays a useful operational view
    rather than an archive. Matches IR's default.
    """
    SessionLocal = _sync_session_factory()
    cutoff = datetime.now(UTC) - timedelta(days=OLD_TASK_DAYS)
    with SessionLocal() as session:
        result = session.execute(
            delete(ImportTask)
            .where(ImportTask.status.in_(["complete", "skipped", "failed"]))
            .where(ImportTask.finished_at < cutoff)
        )
        session.commit()
        return result.rowcount or 0


@celery.task(name="backend.app.tasks.maintenance.backfill_phash")
def backfill_phash() -> int:
    """Recompute phash for stored images that have none (imported before
    FC-2d-i+ii). Keyset-paginated by id (restart-safe), NULL-only fill,
    idempotent. Videos legitimately keep phash NULL. A missing/unreadable
    file is logged and left NULL — never fails the task."""
    SessionLocal = _sync_session_factory()
    updated = 0
    last_id = 0
    with SessionLocal() as session:
        while True:
            rows = session.execute(
                select(ImageRecord)
                .where(ImageRecord.id > last_id)
                .where(ImageRecord.phash.is_(None))
                .where(ImageRecord.mime.like("image/%"))
                .order_by(ImageRecord.id.asc())
                .limit(PHASH_PAGE)
            ).scalars().all()
            if not rows:
                break
            for rec in rows:
                try:
                    with Image.open(rec.path) as im:
                        ph = compute_phash(im)
                except Exception as exc:
                    log.warning(
                        "backfill_phash: unreadable %s: %s", rec.path, exc
                    )
                    ph = None
                if ph is not None and rec.phash is None:
                    rec.phash = ph
                    updated += 1
            session.commit()
            last_id = rows[-1].id
    return updated