"""generate_thumbnail task: PIL/ffmpeg thumbnail generation on the thumbnail queue.

Lives separately from import_file because thumbnails can be regenerated en
masse (FC-2c adds the 'regenerate all' admin action) and they're CPU-bound
so they deserve their own queue lane.
"""

from pathlib import Path

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

from ..celery_app import celery
from ..config import get_config
from ..models import ImageRecord
from ..services.importer import is_video
from ..services.thumbnailer import Thumbnailer

IMAGES_ROOT = Path("/images")


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.thumbnail.generate_thumbnail", bind=True)
def generate_thumbnail(self, image_id: int) -> dict:
    SessionLocal = _sync_session_factory()
    with SessionLocal() as session:
        record = session.get(ImageRecord, image_id)
        if record is None:
            return {"status": "missing", "image_id": image_id}

        thumbnailer = Thumbnailer(images_root=IMAGES_ROOT)
        source = Path(record.path)
        try:
            if is_video(source):
                result = thumbnailer.generate_video_thumbnail(source, record.sha256)
            else:
                result = thumbnailer.generate_image_thumbnail(source, record.sha256)
        except Exception as exc:  # pragma: no cover — thumbnail failure is non-fatal
            return {"status": "failed", "image_id": image_id, "error": f"{type(exc).__name__}: {exc}"}

        record.thumbnail_path = str(result.path)
        session.add(record)
        session.commit()
        return {"status": "ok", "image_id": image_id, "path": str(result.path)}