198 lines
6.2 KiB
Python
198 lines
6.2 KiB
Python
"""
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支付服务层
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处理支付金额计算、订单创建等业务逻辑
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"""
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import logging
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from decimal import Decimal, ROUND_HALF_UP
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logger = logging.getLogger(__name__)
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# 支付金额最小值（单位：元），防止出现负数或零元订单
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MIN_PAYABLE_AMOUNT = Decimal('0.01')
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class PaymentCalculator:
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"""支付金额计算工具"""
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@staticmethod
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def calc_final_amount(original_price: float, discount: float = 0.0) -> Decimal:
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"""
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计算折扣后实付金额
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Args:
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original_price: 原价（元）
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discount: 折扣减免金额（元，非折扣率）
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Returns:
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Decimal: 最终应付金额，最小为 MIN_PAYABLE_AMOUNT
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Example:
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>>> calc_final_amount(99.0, 20.0) -> 79.00
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>>> calc_final_amount(99.0, 120.0) -> 0.01 (折扣超出原价，取最小值)
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"""
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price = Decimal(str(original_price))
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disc = Decimal(str(discount))
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if disc < Decimal('0'):
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raise ValueError(f'折扣金额不能为负数: discount={discount}')
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final = price - disc
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# Bug #35 Fix: 折扣金额超出原价时，final 会变为负数
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# 原代码未做下限保护，直接使用 final 导致支付金额为负
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# 修复：将 final 钳制到 MIN_PAYABLE_AMOUNT，不允许出现零元/负数订单
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if final < MIN_PAYABLE_AMOUNT:
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logger.warning(
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'calc_final_amount: discount exceeds price, clamping to min. '
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'original_price=%.2f discount=%.2f computed=%.2f',
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original_price, discount, final,
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)
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final = MIN_PAYABLE_AMOUNT
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return final.quantize(Decimal('0.01'), rounding=ROUND_HALF_UP)
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class PaymentService:
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"""支付业务服务"""
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def __init__(self):
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self.calculator = PaymentCalculator()
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def create_order(self, user_id: int, product_id: int,
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original_price: float, discount: float = 0.0) -> dict:
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"""
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创建支付订单
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Args:
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user_id: 用户 ID
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product_id: 商品 ID
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original_price: 原价
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discount: 优惠减免（元）
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Returns:
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dict: 订单信息
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"""
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final_amount = self.calculator.calc_final_amount(original_price, discount)
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# 此处可进一步调用第三方支付网关创建预付单
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order = {
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'user_id': user_id,
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'product_id': product_id,
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'original_price': float(original_price),
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'discount': float(discount),
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'final_amount': float(final_amount),
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'status': 'pending',
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}
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logger.info('Order created: %s', order)
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return order
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def apply_coupon(self, original_price: float, coupon_value: float) -> dict:
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"""
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应用优惠券
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Args:
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original_price: 原价
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coupon_value: 券面值
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Returns:
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dict 包含 final_amount 和 saved_amount
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"""
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final = self.calculator.calc_final_amount(original_price, coupon_value)
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price = Decimal(str(original_price))
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saved = price - final
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return {
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'original_price': float(original_price),
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'coupon_value': float(coupon_value),
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'final_amount': float(final),
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'saved_amount': float(saved),
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}
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def validate_payment_params(self, original_price: float, discount: float) -> tuple:
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"""
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校验支付参数合法性
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Returns:
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(valid: bool, error_message: str)
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"""
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if original_price <= 0:
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return False, '原价必须大于 0'
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if discount < 0:
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return False, '折扣金额不能为负数'
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return True, ''
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# ---------------------------------------------------------------------------
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# 退款计算
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# ---------------------------------------------------------------------------
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@staticmethod
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def calc_refund_amount(paid_amount: float, refund_ratio: float = 1.0) -> Decimal:
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"""
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计算退款金额
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Args:
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paid_amount: 实付金额
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refund_ratio: 退款比例 (0~1)，默认全额退款
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Returns:
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Decimal: 退款金额
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"""
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if not (0 < refund_ratio <= 1):
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raise ValueError(f'退款比例不能为负数: refund_ratio={refund_ratio}')
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amount = Decimal(str(paid_amount)) * Decimal(str(refund_ratio))
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return amount.quantize(Decimal('0.01'), rounding=ROUND_HALF_UP)
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def process_refund(self, order_id: str, paid_amount: float,
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refund_ratio: float = 1.0) -> dict:
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"""
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处理退款
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Args:
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order_id: 订单号
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paid_amount: 实付金额
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refund_ratio: 退款比例
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Returns:
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dict: 退款结果
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"""
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refund_amount = self.calc_refund_amount(paid_amount, refund_ratio)
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result = {
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'order_id': order_id,
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'paid_amount': paid_amount,
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'refund_amount': float(refund_amount),
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'refund_ratio': refund_ratio,
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'status': 'refund_pending',
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}
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logger.info('Refund processed: %s', result)
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return result
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def get_price_breakdown(self, original_price: float,
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discount: float = 0.0,
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tax_rate: float = 0.0) -> dict:
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"""
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获取价格明细
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Args:
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original_price: 原价
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discount: 折扣减免（元）
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tax_rate: 税率（0~1）
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Returns:
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dict: 价格明细
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"""
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# line 234 - Bug #35 Fix: calc_final_amount 已处理折扣超出原价的情况
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final_before_tax = self.calculator.calc_final_amount(original_price, discount)
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tax = (final_before_tax * Decimal(str(tax_rate))).quantize(
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Decimal('0.01'), rounding=ROUND_HALF_UP
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)
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total = final_before_tax + tax
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return {
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'original_price': float(original_price),
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'discount': float(discount),
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'subtotal': float(final_before_tax),
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'tax': float(tax),
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'total': float(total),
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}
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