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(