Implement Save As

Windows/MainWindow.xaml

@@ -66,6 +66,11 @@
                         </StackPanel>
                     </xctk:SplitButton.DropDownContent>
                 </xctk:SplitButton>
+                <Button Name="Btn_save_as"
+                        Margin="8, 0, 0, 0"
+                        HorizontalAlignment="Left"
+                        Content="Save As"
+                        Click="Btn_save_as_Click"/>
                 <Button Margin="8,0,0,0"
                         HorizontalAlignment="Left"
                         Click="Btn_chunk_search_Click">

Windows/MainWindow.xaml.buttons.cs

@@ -42,6 +42,10 @@ private void Btn_save_as_json_merge_Click(object sender, RoutedEventArgs e) {
             SaveJson(true);
         }
 
+        private void Btn_save_as_Click(object sender, RoutedEventArgs e) {
+            SaveAs();
+        }
+
         private void Btn_chunk_search_Click(object sender, RoutedEventArgs e) {
             new FindFileInChunk().ShowDialog();
         }

Windows/MainWindow.xaml.cs

@@ -332,12 +332,23 @@ public static void CheckHashAndSize(string targetFile) {
         }
 
         private async void Save() {
+            SaveTo(targetFile);
+        }
+
+        private async void SaveAs() {
             if (string.IsNullOrEmpty(targetFile)) return;
+            SaveTo(GetSaveTargetForTargetFile());
+        }
+
+        private async void SaveTo(string file) {
+            if (string.IsNullOrEmpty(file)) return;
 
             try {
                 var saveData = targetFileType.GetMethod("SaveData", BindingFlags.Static | BindingFlags.Public | BindingFlags.FlattenHierarchy);
                 Debug.Assert(saveData != null, nameof(saveData) + " != null");
-                saveData.Invoke(null, new object[] {fileData, targetFile});
+                saveData.Invoke(null, new object[] { fileData, file });
+                targetFile = file;
+                Title      = Path.GetFileName(file);
 
                 await ShowChangesSaved(true);
             } catch (Exception e) when (!Debugger.IsAttached) {
@@ -683,6 +694,17 @@ private string GetSaveTarget() {
             return sfdResult.ShowDialog() == true ? sfdResult.FileName : null;
         }
 
+        private string GetSaveTargetForTargetFile() {
+            var ext = Path.GetExtension(targetFile);
+            var sfdResult = new SaveFileDialog {
+                Filter           = $"{ext.TrimStart('.').ToUpper()}|*{ext}",
+                FileName         = $"{Path.GetFileNameWithoutExtension(targetFile)}",
+                InitialDirectory = targetFile == null ? string.Empty : Path.GetDirectoryName(targetFile) ?? string.Empty,
+                AddExtension     = true
+            };
+            return sfdResult.ShowDialog() == true ? sfdResult.FileName : null;
+        }
+
         public static Type GetFileType(string targetFile) {
             var fileName = Path.GetFileName(targetFile).ToLower();
             Debug.Assert(fileName != null, nameof(fileName) + " != null");