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

The refresh is scheduled on the event loop instead of a thread because the async psycopg
driver only works from the loop; a bare thread cannot open a session on the async engine.
"""

from __future__ import annotations

import asyncio
import logging
from typing import TYPE_CHECKING

from sqlalchemy.ext.asyncio import AsyncSession

from python.ebook_search.bm25_corpus import load_bm25_corpus, refresh_bm25_corpus

if TYPE_CHECKING:
    from fastapi import FastAPI
    from sqlalchemy.ext.asyncio import AsyncEngine

    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.

    Only called from route handlers, so a running event loop is guaranteed.
    """
    cancel_bm25_refresh(app)

    loop = asyncio.get_running_loop()

    def start_refresh() -> None:
        app.state.bm25_refresh_task = loop.create_task(refresh_bm25_for_app(app))

    app.state.bm25_refresh_timer = loop.call_later(app.state.config.bm25_refresh_delay_seconds, start_refresh)
    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 timer and in-flight refresh task."""
    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")

    existing_task = getattr(app.state, "bm25_refresh_task", None)
    if existing_task is not None:
        if not existing_task.done():
            existing_task.cancel()
        app.state.bm25_refresh_task = None


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


async def refresh_bm25_for_engine(engine: AsyncEngine, config: EbookSearchConfig) -> None:
    """Refresh the BM25 corpus using an async SQLAlchemy engine."""
    async with AsyncSession(engine) as session:
        await refresh_bm25_corpus(session, config)
    load_bm25_corpus.cache_clear()
    logger.info("ebook_bm25_corpus_cache_cleared_after_refresh")