"""数据库连接 — 异步引擎 + 连接池"""
from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession
from app.core.config import settings

engine = create_async_engine(
    settings.DATABASE_URL,
    echo=settings.DEBUG,
    pool_size=20,         # 连接池常驻连接数
    max_overflow=10,      # 超出 pool_size 时最多再创建的连接数
    pool_recycle=3600,    # 连接回收时间（秒），防止 MySQL 8 小时断连
    pool_pre_ping=True,   # 每次取出连接前先 ping 检测可用性
    connect_args={
        "server_settings": {"TimeZone": "Asia/Shanghai"},  # PG 会话级北京时间
    },
)

AsyncSessionLocal = async_sessionmaker(
    engine,
    class_=AsyncSession,
    expire_on_commit=False,
)


async def get_db() -> AsyncSession:
    """FastAPI 依赖注入：每次请求获取一个数据库会话（带事务安全兜底）"""
    async with AsyncSessionLocal() as session:
        try:
            yield session
        except Exception:
            await session.rollback()
            raise
        finally:
            await session.close()