From 9cdb0568ccf30c27a3af81da8194e8bd7a1161b9 Mon Sep 17 00:00:00 2001
From: Gemini Wen <coffeesherk@gmail.com>
Date: Sun, 25 Jan 2026 18:12:15 +0800
Subject: [PATCH] =?UTF-8?q?fix(subscription):=20=E4=BF=AE=E5=A4=8D?=
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- 已过期订阅延长时,从当前时间开始增加天数
- 已过期订阅不允许负向调整(缩短)
- 未过期订阅保持原逻辑,从原过期时间增减

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
---
 .../internal/service/subscription_service.go  | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/backend/internal/service/subscription_service.go b/backend/internal/service/subscription_service.go
index 6b3ac8ab..3c42852e 100644
--- a/backend/internal/service/subscription_service.go
+++ b/backend/internal/service/subscription_service.go
@@ -324,14 +324,29 @@ func (s *SubscriptionService) ExtendSubscription(ctx context.Context, subscripti
 		days = -MaxValidityDays
 	}
 
+	now := time.Now()
+	isExpired := !sub.ExpiresAt.After(now)
+
+	// 如果订阅已过期，不允许负向调整
+	if isExpired && days < 0 {
+		return nil, infraerrors.BadRequest("CANNOT_SHORTEN_EXPIRED", "cannot shorten an expired subscription")
+	}
+
 	// 计算新的过期时间
-	newExpiresAt := sub.ExpiresAt.AddDate(0, 0, days)
+	var newExpiresAt time.Time
+	if isExpired {
+		// 已过期：从当前时间开始增加天数
+		newExpiresAt = now.AddDate(0, 0, days)
+	} else {
+		// 未过期：从原过期时间增加/减少天数
+		newExpiresAt = sub.ExpiresAt.AddDate(0, 0, days)
+	}
+
 	if newExpiresAt.After(MaxExpiresAt) {
 		newExpiresAt = MaxExpiresAt
 	}
 
 	// 检查新的过期时间必须大于当前时间
-	now := time.Now()
 	if !newExpiresAt.After(now) {
 		return nil, ErrAdjustWouldExpire
 	}