feat(share): reuse existing share and direct links per file

backend/database.js

@@ -1354,6 +1354,31 @@ const ShareDB = {
     return db.prepare('SELECT * FROM shares WHERE id = ?').get(id);
   },
 
+  // 按目标路径查找已存在分享（用于复用）
+  findExistingByTarget(userId, options = {}) {
+    const {
+      share_type = 'file',
+      file_path = '',
+      storage_type = 'oss'
+    } = options;
+
+    return db.prepare(`
+      SELECT *
+      FROM shares
+      WHERE user_id = ?
+        AND share_type = ?
+        AND share_path = ?
+        AND COALESCE(storage_type, 'oss') = ?
+      ORDER BY id DESC
+      LIMIT 1
+    `).get(
+      userId,
+      share_type,
+      file_path,
+      storage_type || 'oss'
+    );
+  },
+
   // 验证分享密码
   verifyPassword(plainPassword, hashedPassword) {
     return bcrypt.compareSync(plainPassword, hashedPassword);
@@ -1492,6 +1517,28 @@ const DirectLinkDB = {
     return db.prepare('SELECT * FROM direct_links WHERE id = ?').get(id);
   },
 
+  // 按目标路径查找已存在直链（用于复用）
+  findExistingByTarget(userId, options = {}) {
+    const {
+      file_path = '',
+      storage_type = 'oss'
+    } = options;
+
+    return db.prepare(`
+      SELECT *
+      FROM direct_links
+      WHERE user_id = ?
+        AND file_path = ?
+        AND COALESCE(storage_type, 'oss') = ?
+      ORDER BY id DESC
+      LIMIT 1
+    `).get(
+      userId,
+      file_path,
+      storage_type || 'oss'
+    );
+  },
+
   getUserLinks(userId) {
     return db.prepare(`
       SELECT *

backend/server.js

@@ -7263,6 +7263,43 @@ app.post('/api/share/create', authMiddleware, (req, res) => {
       });
     }
 
+    const storageType = req.user.current_storage_type || 'oss';
+    const existingShare = ShareDB.findExistingByTarget(req.user.id, {
+      share_type: actualShareType,
+      file_path: normalizedSharePath,
+      storage_type: storageType
+    });
+
+    if (existingShare) {
+      const shareUrl = `${getSecureBaseUrl(req)}/s/${existingShare.share_code}`;
+      const securityPolicy = getSharePolicySummary(existingShare);
+
+      logShare(
+        req,
+        'reuse_share',
+        `用户复用现有分享: ${actualShareType === 'file' ? '文件' : '目录'} ${normalizedSharePath}`,
+        {
+          shareId: existingShare.id,
+          shareCode: existingShare.share_code,
+          sharePath: normalizedSharePath,
+          shareType: existingShare.share_type
+        }
+      );
+
+      return res.json({
+        success: true,
+        message: '已复用现有分享链接',
+        reused: true,
+        share_id: existingShare.id,
+        share_code: existingShare.share_code,
+        share_url: shareUrl,
+        share_type: existingShare.share_type,
+        expires_at: existingShare.expires_at,
+        has_password: !!existingShare.share_password,
+        security_policy: securityPolicy
+      });
+    }
+
     SystemLogDB.log({
       level: 'info',
       category: 'share',
@@ -7296,7 +7333,7 @@ app.post('/api/share/create', authMiddleware, (req, res) => {
 
     // 更新分享的存储类型
     db.prepare('UPDATE shares SET storage_type = ? WHERE id = ?')
-      .run(req.user.current_storage_type || 'oss', result.id);
+      .run(storageType, result.id);
 
     const shareUrl = `${getSecureBaseUrl(req)}/s/${result.share_code}`;
 
@@ -7331,6 +7368,7 @@ app.post('/api/share/create', authMiddleware, (req, res) => {
     res.json({
       success: true,
       message: '分享链接创建成功',
+      reused: false,
       share_code: result.share_code,
       share_url: shareUrl,
       share_type: result.share_type,
@@ -7489,6 +7527,40 @@ app.post('/api/direct-link/create',
         : (normalizedPath.split('/').pop() || 'download.bin');
 
       const storageType = req.user.current_storage_type || 'oss';
+      const existingLink = DirectLinkDB.findExistingByTarget(req.user.id, {
+        file_path: normalizedPath,
+        storage_type: storageType
+      });
+
+      if (existingLink) {
+        const directUrl = `${getSecureBaseUrl(req)}/d/${existingLink.link_code}`;
+
+        logShare(
+          req,
+          'reuse_direct_link',
+          `用户复用直链: ${normalizedPath}`,
+          {
+            linkId: existingLink.id,
+            linkCode: existingLink.link_code,
+            filePath: normalizedPath,
+            storageType
+          }
+        );
+
+        return res.json({
+          success: true,
+          message: '已复用现有直链',
+          reused: true,
+          link_id: existingLink.id,
+          link_code: existingLink.link_code,
+          file_path: normalizedPath,
+          file_name: existingLink.file_name || resolvedFileName,
+          storage_type: storageType,
+          expires_at: existingLink.expires_at || null,
+          direct_url: directUrl
+        });
+      }
+
       const directLink = DirectLinkDB.create(req.user.id, {
         file_path: normalizedPath,
         file_name: resolvedFileName,
@@ -7514,6 +7586,7 @@ app.post('/api/direct-link/create',
       res.json({
         success: true,
         message: '直链创建成功',
+        reused: false,
         link_id: directLink.id,
         link_code: directLink.link_code,
         file_path: normalizedPath,