"""SQLAlchemy 异步引擎与 Session 工厂"""
from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession
from sqlalchemy.orm import Session
from typing import AsyncGenerator
from app.config import settings

# ── 异步引擎（FastAPI 业务层使用）─────────────────────────────
async_engine = create_async_engine(
    settings.DATABASE_URL,
    pool_size=settings.DB_POOL_SIZE,
    max_overflow=settings.DB_MAX_OVERFLOW,
    pool_pre_ping=True,          # 自动检测断连
    pool_recycle=3600,           # 每小时回收连接，防止 MySQL 8h 超时
    echo=settings.DEBUG,
)

AsyncSessionLocal = async_sessionmaker(
    bind=async_engine,
    class_=AsyncSession,
    expire_on_commit=False,
    autoflush=False,
    autocommit=False,
)


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI Depends 注入用"""
    async with AsyncSessionLocal() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise
        finally:
            await session.close()