fix: handle one-to-many video-subtitle mapping

- Detect if multiple subtitles exist for a single video
- Retain language suffix if one-to-many mapping is found
- Improve merging of items with same keys
  - Group items by non-empty keys and merge them
  - Ensure the first non-empty video and all non-empty subtitles are kept
  - Keep items with empty keys unchanged
  - Update method signature to accept IReadOnlyList

SubRenamer/Matcher/Helper.cs

@@ -19,39 +19,40 @@ public static class Helper
         }
         return "";
     }
-
-    public static void MergeSameKeysItems(List<MatchItem> items)
+
+    /// <summary>
+    /// Merges items with the same non-empty keys by grouping them.
+    /// Assuming the mapping between the video and the subtitles is one-to-many (1 to N).
+    /// Each group is merged into a new list where the first non-empty video
+    /// is selected and all non-empty subtitles are kept.
+    /// </summary>
+    /// <param name="items">A read-only list of MatchItem objects to be merged by key.</param>
+    /// <returns>
+    /// A list of MatchItem objects where keys are merged, each key associated with
+    /// its first non-empty video and corresponding subtitles.
+    /// </returns>
+    public static List<MatchItem> MergeSameKeysItems(IReadOnlyList<MatchItem> items)
     {
-        for (var i = 0; i < items.Count; i++)
+        // Group items by non-empty keys, filtering out items with null or empty keys
+        var groupedItems = items
+            .Where(item => !string.IsNullOrEmpty(item.Key))
+            .GroupBy(item => item.Key);
+
+        // Create the merged list of MatchItems
+        var result = new List<MatchItem>();
+        foreach (var group in groupedItems)
         {
-            var item = items[i];
-            if (string.IsNullOrEmpty(item.Key)) continue;
-            //筛选出所有Subtitles用于匹配多个字幕
-            if (item.Subtitle != "")
-            {
-                for (var j = 0; j < items.Count; j++)
-                {
-                    var other = items[j];
-                    if (item.Key == other.Key && other.Subtitle == "")
-                    {
-                        item.Video = !string.IsNullOrEmpty(item.Video) ? item.Video : other.Video;
-                        other.Status = "Paired";
-                    }
-                }
-            }
-            //将已匹配完成的只包含Video的item删除
-            if (i == (items.Count - 1))
-            {
-                for (i = 0; i < items.Count; i++)
-                {
-                    if (items[i].Status == "Paired")
-                    {
-                        items.RemoveAt(i);
-                        i--;
-                    }
-                }
-            }
+            var video = group.FirstOrDefault(item => !string.IsNullOrEmpty(item.Video))?.Video ?? "";
+            var subtitles = group.Where(item => !string.IsNullOrEmpty(item.Subtitle)).Select(item => item.Subtitle);
+
+            // Add a new MatchItem for each subtitle under the same key and video
+            result.AddRange(subtitles.Select(subtitle => new MatchItem(group.Key, video, subtitle)));
         }
+
+        // Keep items with empty keys
+        result.AddRange(items.Where(item => string.IsNullOrEmpty(item.Key)));
+
+        return result;
     }
 
     public static void MoveEmptyKeyItemsToLast(List<MatchItem> items)

SubRenamer/Services/DialogService.cs

@@ -63,9 +63,6 @@ public async Task OpenItemEdit(MatchItem item, ObservableCollection<MatchItem> c
         await dialog.ShowDialog(_target);
         if (cancel) throw new UserCancelDialogException();
         var selected = store.GetResult();
-        //选择全部保留时自动勾选保留语言后缀选项
-        var config = Config.Get(); 
-        if (selected == "全部保留") config.KeepLangExt = true;
         return selected == "全部保留" ? null : selected;
     }
 

SubRenamer/Services/RenameService.cs

@@ -18,13 +18,18 @@ public void UpdateRenameTaskList(IEnumerable<MatchItem> matchList, Collection<Re
     {
         destList.Clear();
 
+        // 检查是否存在视频字幕一对多的情况，若存在则保留语言后缀
+        // @see https://github.com/qwqcode/SubRenamer/pull/54
+        var hasOneVideo2ManySubtitles = matchList.GroupBy(x => x.Video).Any(g => g.Count() > 1);
+        var keepLangExt = Config.Get().KeepLangExt || hasOneVideo2ManySubtitles;
+
         foreach (var item in matchList)
         {
             if (string.IsNullOrEmpty(item.Subtitle) || string.IsNullOrEmpty(item.Video)) continue;
 
             // 提取字幕文件语言后缀
             var subSuffix = "";
-            if (Config.Get().KeepLangExt) {
+            if (keepLangExt) {
                 var subSplit = Path.GetFileNameWithoutExtension(item.Subtitle).Split('.');
                 if (subSplit.Length > 1) subSuffix = "." + subSplit[^1];
             }