Prevent choosing invalid from/to dates

DiscordChatExporter.Gui/ViewModels/ExportSetupViewModel.cs

@@ -93,6 +93,12 @@ namespace DiscordChatExporter.Gui.ViewModels
             // Save format
             _settingsService.LastExportFormat = SelectedFormat;
 
+            // Clamp 'from' and 'to' values
+            if (From > To)
+                From = To;
+            if (To < From)
+                To = From;
+
             // Start export
             MessengerInstance.Send(new StartExportMessage(Channel, FilePath, SelectedFormat, From, To));
         }

DiscordChatExporter.Gui/Views/ExportSetupDialog.xaml

@@ -36,18 +36,22 @@
                 <ColumnDefinition Width="*" />
             </Grid.ColumnDefinitions>
             <DatePicker
+                x:Name="FromDatePicker"
                 Grid.Row="0"
                 Grid.Column="0"
                 Margin="16,20,8,8"
                 materialDesign:HintAssist.Hint="From (optional)"
                 materialDesign:HintAssist.IsFloating="True"
+                DisplayDateEnd="{Binding SelectedDate, ElementName=ToDatePicker}"
                 SelectedDate="{Binding From}" />
             <DatePicker
+                x:Name="ToDatePicker"
                 Grid.Row="0"
                 Grid.Column="1"
                 Margin="8,20,16,8"
                 materialDesign:HintAssist.Hint="To (optional)"
                 materialDesign:HintAssist.IsFloating="True"
+                DisplayDateStart="{Binding SelectedDate, ElementName=FromDatePicker}"
                 SelectedDate="{Binding To}" />
         </Grid>