Refine WinUI shell and improve render diagnostics

AmiReel.WinUI/MainPage.xaml.cs

@@ -1,6 +1,7 @@
 using System.Collections.ObjectModel;
 using System.Diagnostics;
 using System.Globalization;
+using System.Text;
 using AmigaDB.VideoRenderer.Models;
 using AmigaDB.VideoRenderer.Services;
 using Microsoft.UI.Xaml;
@@ -15,7 +16,11 @@ public sealed partial class MainPage : Page
 {
     private readonly ObservableCollection<string> _inputs = [];
     private readonly AppSettings _loadedSettings;
+    private readonly StringBuilder _pendingLog = new();
+    private readonly object _logLock = new();
     private CancellationTokenSource? _renderCancellation;
+    private string? _lastRenderedFile;
+    private bool _logFlushScheduled;
 
     public MainPage()
     {
@@ -107,7 +112,9 @@ public sealed partial class MainPage : Page
             _renderCancellation = new CancellationTokenSource();
             Progress<RenderProgress> progress = new(UpdateProgress);
             await new RenderPipeline().RenderAsync(settings, progress, AppendLog, _renderCancellation.Token);
+            _lastRenderedFile = Path.Combine(settings.OutputDirectory, settings.OutputName + "_final.mp4");
             OpenOutputButton.IsEnabled = true;
+            PreviewRenderedButton.IsEnabled = File.Exists(_lastRenderedFile);
             await ShowMessageAsync("Render complete", "The AmiReel render completed successfully.");
         }
         catch (OperationCanceledException)
@@ -118,7 +125,7 @@ public sealed partial class MainPage : Page
         {
             AppendLog("ERROR: " + exception);
             StageText.Text = "Failed";
-            await ShowMessageAsync("Render failed", exception.Message);
+            await ShowMessageAsync("Render failed", UserFacingErrors.Summarize(exception));
         }
         finally
         {
@@ -141,6 +148,18 @@ public sealed partial class MainPage : Page
             Process.Start(new ProcessStartInfo("explorer.exe", OutputFolderBox.Text) { UseShellExecute = true });
     }
 
+    private void PreviewSource_Click(object sender, RoutedEventArgs e)
+    {
+        if (InputList.SelectedItem is string path)
+            OpenPreview(path);
+    }
+
+    private void PreviewRendered_Click(object sender, RoutedEventArgs e)
+    {
+        if (!string.IsNullOrWhiteSpace(_lastRenderedFile) && File.Exists(_lastRenderedFile))
+            OpenPreview(_lastRenderedFile);
+    }
+
     private void ThemeBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
     {
         if (!IsLoaded) return;
@@ -191,11 +210,39 @@ public sealed partial class MainPage : Page
         StatusText.Text = value.Message;
     }
 
+    private void OpenPreview(string mediaPath)
+    {
+        if (!File.Exists(mediaPath))
+            return;
+
+        Process.Start(new ProcessStartInfo(mediaPath) { UseShellExecute = true });
+    }
+
     private void AppendLog(string line)
     {
+        lock (_logLock)
+        {
+            _pendingLog.AppendLine(line);
+            if (_logFlushScheduled)
+                return;
+
+            _logFlushScheduled = true;
+        }
+
         _ = DispatcherQueue.TryEnqueue(() =>
         {
-            LogBox.Text += line + Environment.NewLine;
+            string chunk;
+            lock (_logLock)
+            {
+                chunk = _pendingLog.ToString();
+                _pendingLog.Clear();
+                _logFlushScheduled = false;
+            }
+
+            if (chunk.Length == 0)
+                return;
+
+            LogBox.Text += chunk;
             LogBox.Select(LogBox.Text.Length, 0);
         });
     }
@@ -207,7 +254,7 @@ public sealed partial class MainPage : Page
             EndCardBox.Text.Trim(),
             FfmpegPathBox.Text.Trim(),
             FfprobePathBox.Text.Trim(),
-            string.Empty,
+            _loadedSettings.PreviewPlayerPath,
             SelectedTheme(),
             SelectedEncoder(),
             TrimBox.Text.Trim(),
@@ -248,6 +295,11 @@ public sealed partial class MainPage : Page
         EncoderBox.SelectedIndex = 0;
     }
 
+    private void InputList_SelectionChanged(object sender, SelectionChangedEventArgs e)
+    {
+        PreviewSourceButton.IsEnabled = InputList.SelectedItem is string;
+    }
+
     private void ApplyTheme(string theme)
     {
         RequestedTheme = string.Equals(theme, "Light", StringComparison.OrdinalIgnoreCase)