安全存储首购优惠

def validate_discount(discount_code, purchase_amount):
    valid_codes = {
        "SAVE10": 0.10,
        "SAVE20": 0.20,
        "FREE30": 30  # 免费30天试用
    }
    
    if discount_code in valid_codes:
        if isinstance(valid_codes[discount_code], int):  # 检查是否为免费试用期
            return f"Congratulations! You've got a {valid_codes[discount_code]} day free trial."
        else:
            savings = purchase_amount * valid_codes[discount_code]
            return f"Discount applied! You saved ${savings:.2f}."
    else:
        return "Invalid discount code. Please check and try again."

# 使用示例
print(validate_discount("SAVE10", 100))  # 输出: Discount applied! You saved $10.00.
print(validate_discount("FREE30", 0))    # 输出: Congratulations! You've got a 30 day free trial.