from sqlalchemy.orm import Session
from app.models.user_account import UserAccountDB, AccountDetailDB, AccountDetailType
from decimal import Decimal
from typing import Optional

class AccountManager:
    """用户账户管理类"""
    
    def __init__(self, db: Session):
        self.db = db
    
    def get_or_create_account(self, user_id: int) -> UserAccountDB:
        """获取或创建用户账户"""
        account = self.db.query(UserAccountDB).filter(
            UserAccountDB.user_id == user_id
        ).first()
        
        if not account:
            account = UserAccountDB(
                user_id=user_id,
                balance=0
            )
            self.db.add(account)
            self.db.flush()
        
        return account
    
    def change_balance(
        self, 
        user_id: int, 
        amount: float, 
        description: str,
        transaction_id: Optional[str] = None
    ) -> UserAccountDB:
        """
        变更用户余额
        
        Args:
            user_id: 用户ID
            amount: 变更金额（正数为收入，负数为支出）
            description: 变更说明
            transaction_id: 关联订单号
        
        Returns:
            更新后的账户信息
        
        Raises:
            Exception: 余额不足等异常
        """
        # 转换为 Decimal 以确保精确计算
        decimal_amount = Decimal(str(amount))
        
        # 获取或创建账户
        account = self.get_or_create_account(user_id)
        
        # 检查余额是否充足（支出时）
        if decimal_amount < 0 and account.balance + decimal_amount < 0:
            raise Exception("账户余额不足")
        
        # 更新余额
        account.balance += decimal_amount
        
        # 记录账户明细
        detail = AccountDetailDB(
            user_id=user_id,
            amount=decimal_amount,
            type=AccountDetailType.INCOME if decimal_amount > 0 else AccountDetailType.EXPENSE,
            description=description,
            transaction_id=transaction_id
        )
        self.db.add(detail)
        
        return account