DYN-8797: Optimize AddToRecent files

src/DynamoCoreWpf/Controls/StartPage.xaml.cs

@@ -211,7 +211,7 @@ internal StartPageViewModel(DynamoViewModel dynamoViewModel, bool isFirstRun)
             #endregion
 
             var dvm = this.DynamoViewModel;
-            RefreshRecentFileList(dvm.RecentFiles);
+            RefreshRecentFileList(dvm.RecentFiles, true);
             RefreshBackupFileList(dvm.Model.PreferenceSettings.BackupFiles);
             dvm.RecentFiles.CollectionChanged += OnRecentFilesChanged;
         }
@@ -404,27 +404,57 @@ public string BackupTitle
 
         private void OnRecentFilesChanged(object sender, NotifyCollectionChangedEventArgs e)
         {
-            RefreshRecentFileList(sender as IEnumerable<string>);
+            //when we are just moving existing files, no need to refresh the complete list
+            if (e.Action == NotifyCollectionChangedAction.Move)
+            {
+                recentFiles.Move(e.OldStartingIndex, e.NewStartingIndex);
+            }
+            else if (e.Action == NotifyCollectionChangedAction.Add)
+            {
+                var newItems = e.NewItems?.Cast<string>();
+                if (newItems != null)
+                {
+                    RefreshRecentFileList(newItems);
+                }
+            }
+            else if (e.Action == NotifyCollectionChangedAction.Remove)
+            {
+                recentFiles.RemoveRange(e.OldStartingIndex, recentFiles.Count - e.OldStartingIndex);
+            }
+            else
+            {
+                RefreshRecentFileList(sender as IEnumerable<string>, true);
+            }
         }
 
         #endregion
 
         #region Private Class Helper Methods
 
-        private void RefreshRecentFileList(IEnumerable<string> filePaths)
+        private void RefreshRecentFileList(IEnumerable<string> filePaths, bool fullRefresh = false)
         {
-            RefreshFileList(recentFiles, filePaths);
+            RefreshFileList(recentFiles, filePaths, fullRefresh);
         }
 
         private void RefreshBackupFileList(IEnumerable<string> filePaths)
         {
-            RefreshFileList(backupFiles, filePaths);
+            RefreshFileList(backupFiles, filePaths, true);
         }
 
+        /// <summary>
+        /// Refreshes the list of files in the specified collection. If fullRefresh is true,
+        /// discards the current list and regenerates all file items based on the provided file paths.
+        /// </summary>
+        /// <param name="files">Files currently in the recent files list</param>
+        /// <param name="filePaths">New files path which will be used to update the current list</param>
+        /// <param name="fullRefresh">If true, will discard the current list and regenerate all file items based on the provided file paths</param>
         private void RefreshFileList(ObservableCollection<StartPageListItem> files,
-            IEnumerable<string> filePaths)
+            IEnumerable<string> filePaths, bool fullRefresh = false)
         {
-            files.Clear();
+            if (fullRefresh)
+            {
+                files.Clear();
+            }
             foreach (var filePath in filePaths.Where(x => x != null))
             {
                 try
@@ -441,7 +471,7 @@ private void RefreshFileList(ObservableCollection<StartPageListItem> files,
                     // deserializes the file only once
                     var properties = GetFileProperties(filePath);
 
-                    files.Add(new StartPageListItem(caption)
+                    var startItem = new StartPageListItem(caption)
                     {
                         ContextData = filePath,
                         ToolTip = filePath,
@@ -451,8 +481,16 @@ private void RefreshFileList(ObservableCollection<StartPageListItem> files,
                         Author = properties.author,
                         DateModified = properties.date,
                         ClickAction = StartPageListItem.Action.FilePath,
+                    };
 
-                    }); 
+                    if (fullRefresh)
+                    {
+                        files.Add(startItem);
+                    }
+                    else
+                    {
+                        files.Insert(0, startItem);
+                    }
                 }
                 catch (ArgumentException ex)
                 {

src/DynamoCoreWpf/ViewModels/Core/DynamoViewModel.cs

@@ -1830,17 +1830,35 @@ private void OnRuleEvaluationResultsCollectionChanged(object sender, NotifyColle
             RaisePropertyChanged(nameof(LinterIssuesCount));
         }
 
+        /// <summary>
+        /// Adds the path to the list of recent files.
+        /// We don't do anything if the file is already added and is at the first place,
+        /// we move the file to the start of the list if it is already present,
+        /// or add it to the start of the list if it is not present.
+        /// Every other event, except Move will refresh all the recent files.
+        /// </summary>
+        /// <param name="path"></param>
         internal void AddToRecentFiles(string path)
         {
             if (path == null) return;
 
-            if (RecentFiles.Contains(path))
+            var currIdx = RecentFiles.IndexOf(path);
+            if (currIdx == 0) return;
+            else if (currIdx > 0)
             {
-                RecentFiles.Remove(path);
+                RecentFiles.Move(currIdx, 0);
+                return;
             }
 
             RecentFiles.Insert(0, path);
+            UpdateRecentFiles();
+        }
 
+        /// <summary>
+        /// Update recent files list and limits the number of recent files to the maximum number of recent files as set in the preferences.
+        /// </summary>
+        internal void UpdateRecentFiles()
+        {
             int maxNumRecentFiles = Model.PreferenceSettings.MaxNumRecentFiles;
             if (RecentFiles.Count > maxNumRecentFiles)
             {

src/DynamoCoreWpf/ViewModels/Menu/PreferencesViewModel.cs

@@ -1820,7 +1820,7 @@ private void Model_PropertyChanged(object sender, PropertyChangedEventArgs e)
                     goto default;
                 case nameof(MaxNumRecentFiles):
                     description = Res.ResourceManager.GetString(nameof(Res.PreferencesSettingMaxRecentFiles), System.Globalization.CultureInfo.InvariantCulture);
-                    UpdateRecentFiles();
+                    dynamoViewModel.UpdateRecentFiles();
                     goto default;
                 case nameof(PythonTemplateFilePath):
                     description = Res.ResourceManager.GetString(nameof(Res.PreferencesSettingCustomPythomTemplate), System.Globalization.CultureInfo.InvariantCulture);
@@ -1964,14 +1964,6 @@ private void PythonEnginesChanged(object sender, NotifyCollectionChangedEventArg
                 AddPythonEnginesOptions();
             }
         }
-
-        private void UpdateRecentFiles()
-        {
-            if (dynamoViewModel.RecentFiles.Count > MaxNumRecentFiles)
-            {
-                dynamoViewModel.RecentFiles.RemoveRange(MaxNumRecentFiles, dynamoViewModel.RecentFiles.Count - MaxNumRecentFiles);
-            }
-        }
     }
 
     public class PythonTemplatePathEventArgs : EventArgs