"""Background BM25 refresh tasks for the web app."""

from __future__ import annotations

import logging
from threading import Timer
from typing import TYPE_CHECKING

from sqlalchemy.orm import Session

from python.ebook_search.bm25_corpus import load_bm25_corpus, refresh_bm25_corpus

if TYPE_CHECKING:
    from fastapi import FastAPI
    from sqlalchemy.engine import Engine

    from python.ebook_search.config import EbookSearchConfig

logger = logging.getLogger(__name__)


def schedule_bm25_refresh(app: FastAPI) -> None:
    """Schedule a delayed BM25 corpus refresh, replacing any pending refresh."""
    existing_timer = getattr(app.state, "bm25_refresh_timer", None)
    if existing_timer is not None:
        existing_timer.cancel()

    timer = Timer(app.state.config.bm25_refresh_delay_seconds, refresh_bm25_for_app, args=(app,))
    timer.daemon = True
    timer.start()
    app.state.bm25_refresh_timer = timer
    logger.info(
        "ebook_bm25_refresh_scheduled delay_seconds=%s",
        app.state.config.bm25_refresh_delay_seconds,
    )


def cancel_bm25_refresh(app: FastAPI) -> None:
    """Cancel any pending BM25 corpus refresh."""
    existing_timer = getattr(app.state, "bm25_refresh_timer", None)
    if existing_timer is not None:
        existing_timer.cancel()
        app.state.bm25_refresh_timer = None
        logger.info("ebook_bm25_refresh_cancelled")


def refresh_bm25_for_app(app: FastAPI) -> None:
    """Refresh the BM25 corpus using the app engine and config."""
    try:
        refresh_bm25_for_engine(app.state.engine, app.state.config)
    except Exception:
        logger.exception("ebook_bm25_refresh_failed")


def refresh_bm25_for_engine(engine: Engine, config: EbookSearchConfig) -> None:
    """Refresh the BM25 corpus using a SQLAlchemy engine."""
    with Session(engine) as session:
        refresh_bm25_corpus(session, config)
    load_bm25_corpus.cache_clear()
    logger.info("ebook_bm25_corpus_cache_cleared_after_refresh")