"""Async engine + session factory, created lazily from settings.

The engine is process-global and cached. The API binds a session per request
(see ``app.api.deps``); workers and scripts use :func:`session_scope`.
"""

from collections.abc import AsyncIterator
from contextlib import asynccontextmanager
from functools import lru_cache

from sqlalchemy.ext.asyncio import (
    AsyncEngine,
    AsyncSession,
    async_sessionmaker,
    create_async_engine,
)

from app.core.config import get_settings


@lru_cache
def get_engine() -> AsyncEngine:
    settings = get_settings()
    return create_async_engine(
        settings.database_url,
        echo=settings.db_echo,
        pool_size=settings.db_pool_size,
        max_overflow=settings.db_max_overflow,
        pool_pre_ping=True,  # survive Postgres restarts / idle drops
    )


@lru_cache
def get_sessionmaker() -> async_sessionmaker[AsyncSession]:
    return async_sessionmaker(
        bind=get_engine(),
        expire_on_commit=False,
        autoflush=False,
    )


@asynccontextmanager
async def session_scope() -> AsyncIterator[AsyncSession]:
    """Transactional session for workers/scripts: commit on success, rollback on error."""
    session = get_sessionmaker()()
    try:
        yield session
        await session.commit()
    except Exception:
        await session.rollback()
        raise
    finally:
        await session.close()


async def dispose_engine() -> None:
    """Dispose the pooled engine on shutdown. Safe to call if never initialized."""
    if get_engine.cache_info().currsize:
        await get_engine().dispose()
        get_engine.cache_clear()
        get_sessionmaker.cache_clear()