update pay function

app.py

@@ -1427,6 +1427,10 @@ def calculate_subscription_price_simple(user_id, to_plan_name, to_cycle, promo_c
                                 remaining_value = current_price * (remaining_days / total_days)
                                 # 实付金额 = 新套餐价格 - 剩余价值
                                 final_price = max(0, price - remaining_value)
+
+                                # 如果剩余价值 >= 新套餐价格，标记为免费升级
+                                if remaining_value >= price:
+                                    final_price = 0
             elif current_plan == 'max' and to_plan_name == 'pro':
                 # 降级：Max → Pro，到期后切换，全价购买
                 is_downgrade = True
@@ -1786,6 +1790,89 @@ def calculate_subscription_price():
         }), 500
 
 
+@app.route('/api/subscription/free-upgrade', methods=['POST'])
+@login_required
+def free_upgrade_subscription():
+    """
+    免费升级订阅（当剩余价值 >= 新套餐价格时）
+
+    Request Body:
+        {
+            "plan_name": "max",
+            "billing_cycle": "yearly"
+        }
+    """
+    try:
+        data = request.get_json()
+        plan_name = data.get('plan_name')
+        billing_cycle = data.get('billing_cycle')
+
+        if not plan_name or not billing_cycle:
+            return jsonify({'success': False, 'error': '参数不完整'}), 400
+
+        user_id = current_user.id
+
+        # 计算价格，验证是否可以免费升级
+        price_result = calculate_subscription_price_simple(user_id, plan_name, billing_cycle, None)
+
+        if 'error' in price_result:
+            return jsonify({'success': False, 'error': price_result['error']}), 400
+
+        # 检查是否为升级且实付金额为0
+        if not price_result.get('is_upgrade') or price_result.get('final_amount', 1) > 0:
+            return jsonify({'success': False, 'error': '当前情况不符合免费升级条件'}), 400
+
+        # 获取当前订阅
+        subscription = UserSubscription.query.filter_by(user_id=user_id).first()
+        if not subscription:
+            return jsonify({'success': False, 'error': '未找到订阅记录'}), 404
+
+        # 计算新的到期时间（按剩余价值折算）
+        remaining_value = price_result.get('remaining_value', 0)
+        new_plan_price = price_result.get('new_plan_price', 0)
+
+        if new_plan_price > 0:
+            # 计算可以兑换的新套餐天数
+            value_ratio = remaining_value / new_plan_price
+
+            cycle_days_map = {
+                'monthly': 30,
+                'quarterly': 90,
+                'semiannual': 180,
+                'yearly': 365
+            }
+            new_cycle_days = cycle_days_map.get(billing_cycle, 365)
+
+            # 新的到期天数 = 周期天数 × 价值比例
+            new_days = int(new_cycle_days * value_ratio)
+
+            # 更新订阅信息
+            subscription.subscription_type = plan_name
+            subscription.billing_cycle = billing_cycle
+            subscription.start_date = datetime.utcnow()
+            subscription.end_date = datetime.utcnow() + timedelta(days=new_days)
+            subscription.subscription_status = 'active'
+            subscription.updated_at = datetime.utcnow()
+
+            db.session.commit()
+
+            return jsonify({
+                'success': True,
+                'message': f'升级成功！您的{plan_name.upper()}版本将持续{new_days}天',
+                'data': {
+                    'subscription_type': plan_name,
+                    'end_date': subscription.end_date.isoformat(),
+                    'days': new_days
+                }
+            })
+        else:
+            return jsonify({'success': False, 'error': '价格计算异常'}), 500
+
+    except Exception as e:
+        db.session.rollback()
+        return jsonify({'success': False, 'error': f'升级失败: {str(e)}'}), 500
+
+
 @app.route('/api/payment/create-order', methods=['POST'])
 def create_payment_order():
     """
@@ -1819,6 +1906,15 @@ def create_payment_order():
         amount = price_result['final_amount']
         subscription_type = price_result.get('subscription_type', 'new')  # new 或 renew
 
+        # 检查是否为免费升级（金额为0）
+        if amount <= 0 and price_result.get('is_upgrade'):
+            return jsonify({
+                'success': False,
+                'error': '当前剩余价值可直接免费升级，请使用免费升级功能',
+                'should_free_upgrade': True,
+                'price_info': price_result
+            }), 400
+
         # 创建订单
         try:
             order = PaymentOrder(

src/components/Subscription/SubscriptionContentNew.tsx

@@ -270,6 +270,46 @@ export default function SubscriptionContentNew() {
     try {
       const price = priceInfo?.final_amount || getCurrentPrice(selectedPlan);
 
+      // 检查是否为免费升级（剩余价值足够抵扣新套餐价格）
+      if (price === 0 && priceInfo?.is_upgrade) {
+        const response = await fetch('/api/subscription/free-upgrade', {
+          method: 'POST',
+          headers: {
+            'Content-Type': 'application/json',
+          },
+          credentials: 'include',
+          body: JSON.stringify({
+            plan_name: selectedPlan.name,
+            billing_cycle: selectedCycle,
+          }),
+        });
+
+        const data = await response.json();
+        if (data.success) {
+          subscriptionEvents.trackPaymentSuccessful({
+            planName: selectedPlan.name,
+            paymentMethod: 'free_upgrade',
+            amount: 0,
+            orderId: 'free_upgrade',
+            transactionId: 'free_upgrade',
+          });
+
+          toast({
+            title: '升级成功！',
+            description: data.message,
+            status: 'success',
+            duration: 5000,
+            isClosable: true,
+          });
+
+          onClose();
+          setTimeout(() => window.location.reload(), 2000);
+          return;
+        } else {
+          throw new Error(data.error || '免费升级失败');
+        }
+      }
+
       subscriptionEvents.trackPaymentInitiated({
         planName: selectedPlan.name,
         paymentMethod: 'wechat_pay',
@@ -1122,7 +1162,9 @@ export default function SubscriptionContentNew() {
                         <HStack spacing={2}>
                           <Icon as={FaCheck} color="green.400" />
                           <Text color="green.400" fontSize="sm" fontWeight="medium">
-                            升级到{selectedPlan.displayName}，立即生效！按差价补缴费用
+                            {priceInfo.final_amount === 0
+                              ? `恭喜！您的当前订阅剩余价值足够直接升级到${selectedPlan.displayName}，无需支付额外费用！`
+                              : `升级到${selectedPlan.displayName}，立即生效！按差价补缴费用`}
                           </Text>
                         </HStack>
                       </Box>
@@ -1293,7 +1335,9 @@ export default function SubscriptionContentNew() {
                     bgGradient: 'linear-gradient(135deg, #F4E3A7, #D4AF37)',
                   }}
                 >
-                  创建微信支付订单
+                  {priceInfo?.is_upgrade && priceInfo?.final_amount === 0
+                    ? '立即免费升级'
+                    : '创建微信支付订单'}
                 </Button>
               </VStack>
             ) : (

src/views/Pages/Account/subscription-content.tsx

@@ -163,7 +163,7 @@ export const subscriptionConfig = {
     },
     {
       question: 'Pro用户如何升级到Max？',
-      answer: '从Pro升级到Max需要补差价，升级后立即生效。系统会根据您Pro订阅的剩余价值计算需要补缴的费用。支付成功后，您将立即获得Max版本的所有功能。',
+      answer: '从Pro升级到Max需要补差价，升级后立即生效。系统会根据您Pro订阅的剩余价值计算需要补缴的费用。支付成功后，您将立即获得Max版本的所有功能。\n\n特别说明：如果您的Pro订阅剩余价值超过或等于Max套餐的价格，系统将自动为您免费升级到Max版本，无需支付额外费用。升级后的有效期将根据剩余价值按比例计算。例如：您的Pro年付版本剩余价值为1200元，选择Max月付版本（998元/月），系统将为您提供约36天的Max版本使用时长（1200÷998×30天）。',
     },
     {
       question: 'Max用户可以切换到Pro吗？',