from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy import text
from config import settings


class Base(DeclarativeBase):
    """SQLAlchemy ORM 基类，所有数据库模型均继承此类。"""
    pass


# 异步数据库引擎，连接池大小 20，最大溢出 40，启用连接健康检查
async_engine = create_async_engine(
    settings.DATABASE_URL,
    pool_size=20,
    max_overflow=40,
    pool_pre_ping=True,
    pool_recycle=3600,
    echo=False,
)

# 异步数据库会话工厂，用于创建数据库会话实例
AsyncSessionLocal = async_sessionmaker(
    async_engine,
    class_=AsyncSession,
    expire_on_commit=False,
)


async def init_db():
    """初始化数据库：创建所有表并执行增量迁移。"""
    async with async_engine.begin() as conn:
        from models import Base as MBase
        await conn.run_sync(MBase.metadata.create_all)

    await _run_migrations()


async def _run_migrations():
    """执行数据库增量迁移，在已有表上安全添加新字段。"""
    async with async_engine.begin() as conn:
        await conn.execute(text(
            "ALTER TABLE flow_definitions ADD COLUMN IF NOT EXISTS published_version_id UUID REFERENCES flow_versions(id)"
        ))
        await conn.execute(text(
            "ALTER TABLE flow_definitions ADD COLUMN IF NOT EXISTS draft_definition_json JSONB"
        ))


async def get_db():
    """FastAPI 依赖注入函数，提供数据库会话，自动提交或回滚事务。"""
    async with AsyncSessionLocal() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise
        finally:
            await session.close()