"""请求级数据库会话依赖与引擎生命周期。

引擎由应用实例持有（create_app 时创建）：一个应用一个引擎与连接池，
避免模块级引擎跨事件循环复用连接。
"""

from collections.abc import AsyncIterator
from typing import Annotated

from fastapi import Depends, FastAPI, Request
from sqlalchemy.ext.asyncio import AsyncEngine, AsyncSession, async_sessionmaker

from app.db.base import create_engine, create_session_factory


def init_engine(app: FastAPI) -> async_sessionmaker[AsyncSession]:
    """在 app.state 上初始化引擎与会话工厂（应用启动时调用一次）。"""
    engine: AsyncEngine = create_engine()
    app.state.engine = engine
    factory = create_session_factory(engine)
    app.state.session_factory = factory
    return factory


async def get_db(request: Request) -> AsyncIterator[AsyncSession]:
    """每请求一个会话：成功提交、异常回滚。"""
    factory: async_sessionmaker[AsyncSession] = request.app.state.session_factory
    async with factory() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise


DbSession = Annotated[AsyncSession, Depends(get_db)]