from __future__ import annotations

from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine

from app.core.config import get_settings


def create_engine():
    """
    创建异步 Engine。

    注意：连接串从环境变量 `DATABASE_URL` 读取。
    """

    settings = get_settings()
    return create_async_engine(settings.database_url, pool_pre_ping=True)


engine = create_engine()

AsyncSessionLocal: async_sessionmaker[AsyncSession] = async_sessionmaker(
    bind=engine,
    expire_on_commit=False,
    autoflush=False,
    autocommit=False,
)


async def get_db() -> AsyncSession:
    """
    FastAPI 依赖：获取数据库会话。
    """

    async with AsyncSessionLocal() as session:
        yield session