"""async engine / session（ARCH §2.3：同进程，async-first）。"""

from __future__ import annotations

from collections.abc import AsyncIterator
from functools import lru_cache

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


@lru_cache
def get_sessionmaker() -> async_sessionmaker[AsyncSession]:
    settings = get_settings()
    engine = create_async_engine(settings.database_url, pool_pre_ping=True)
    return async_sessionmaker(engine, expire_on_commit=False)


async def get_session() -> AsyncIterator[AsyncSession]:
    """FastAPI 依赖：每请求一个 session。"""
    sm = get_sessionmaker()
    async with sm() as session:
        yield session