# 安装依赖：pip install fastapi uvicorn sqlalchemy pydantic
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

# 配置SQLite数据库连接（生产环境建议使用PostgreSQL）
SQLALCHEMY_DATABASE_URL = "sqlite:///./test.db"
engine = create_engine(
    SQLALCHEMY_DATABASE_URL,
    connect_args={"check_same_thread": False},
    echo=True  # 显示生成的SQL语句
)

# 创建数据库会话工厂
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

# 声明性基类
Base = declarative_base()

from sqlalchemy import Column, Integer, String


class User(Base):
    __tablename__ = "users"

    id = Column(Integer, primary_key=True, index=True)
    name = Column(String(50), nullable=False)
    email = Column(String(100), unique=True)
    balance = Column(Integer, default=0)


# 创建数据库表（生产环境建议使用迁移工具）
Base.metadata.create_all(bind=engine)

from pydantic import BaseModel


class UserCreate(BaseModel):
    name: str
    email: str
    balance: int = 0


class UserResponse(BaseModel):
    id: int
    name: str
    email: str
    balance: int

    class Config:
        orm_mode = True  # 启用ORM模式转换

from fastapi import APIRouter, Depends, HTTPException
from sqlalchemy.orm import Session

router = APIRouter()


# 依赖项获取数据库会话
def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


@router.post("/users/", response_model=UserResponse)
def create_user(user: UserCreate, db: Session = Depends(get_db)):
    # 显式开始事务
    transaction = db.begin()
    try:
        db_user = User(**user.dict())
        db.add(db_user)
        db.commit()
        db.refresh(db_user)
        return db_user
    except Exception as e:
        transaction.rollback()
        raise HTTPException(
            status_code=400,
            detail=f"创建用户失败: {str(e)}"
        )

def transfer_funds(sender_id: int, receiver_id: int, amount: int, db: Session):
    transaction = db.begin()
    try:
        # 获取发送方账户
        sender = db.query(User).filter(User.id == sender_id).with_for_update().first()
        if not sender or sender.balance < amount:
            raise ValueError("余额不足或账户不存在")

        # 获取接收方账户
        receiver = db.query(User).filter(User.id == receiver_id).with_for_update().first()
        if not receiver:
            raise ValueError("接收方账户不存在")

        # 执行转账
        sender.balance -= amount
        receiver.balance += amount

        db.commit()
        return {"message": "转账成功"}

    except Exception as e:
        transaction.rollback()
        raise HTTPException(status_code=400, detail=str(e))