"""异步数据库引擎 + 会话。

- engine / SessionLocal:全局单例
- get_session:FastAPI 依赖,按请求注入一个会话
- init_db:启动时建表(MVP 用 create_all;表结构稳定后切 alembic 迁移,对齐 dograh)
"""

from collections.abc import AsyncGenerator

import config
from db.models import Base
from sqlalchemy.ext.asyncio import (
    AsyncSession,
    async_sessionmaker,
    create_async_engine,
)

engine = create_async_engine(config.DATABASE_URL, echo=False, pool_pre_ping=True)
SessionLocal = async_sessionmaker(engine, expire_on_commit=False)


async def get_session() -> AsyncGenerator[AsyncSession, None]:
    async with SessionLocal() as session:
        yield session


async def init_db() -> None:
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)