# v1.4.0 - 税务与合规处理

## 税务计算

```go
func (s *SubscriptionManager) CalculateTax(ctx context.Context, userID int64, amount float64) (float64, error) {
    // 获取用户地区
    user, _ := s.getUser(ctx, userID)
    
    // 根据地区计算税率
    taxRates := map[string]float64{
        "US-CA": 0.0825,  // 加州
        "US-NY": 0.08,    // 纽约
        "EU":    0.20,    // 欧盟VAT
    }
    
    rate := taxRates[user.Region]
    return amount * rate, nil
}
```

## 发票生成

```go
func (s *SubscriptionManager) GenerateInvoice(ctx context.Context, txnID int64) (*Invoice, error) {
    txn, _ := s.dao.GetTransaction(ctx, txnID)
    
    invoice := &Invoice{
        ID:         generateInvoiceID(),
        UserID:     txn.UserID,
        Amount:     txn.Amount,
        Tax:        txn.Tax,
        Total:      txn.Amount + txn.Tax,
        Currency:   txn.Currency,
        Date:       time.Now(),
        LineItems: []LineItem{
            {
                Description: fmt.Sprintf("%s Plan", txn.PlanName),
                Amount:      txn.Amount,
            },
        },
    }
    
    return invoice, nil
}
```