Reloadable configuration, FontService (WIP)

src/GuiApp/Avalonia/FileTime.GuiApp.Font/Services/FontService.cs

@@ -0,0 +1,34 @@
+using System.Reactive.Linq;
+using System.Reactive.Subjects;
+using Avalonia.Media;
+using FileTime.GuiApp.Configuration;
+using Microsoft.Extensions.Options;
+
+namespace FileTime.GuiApp.Services;
+
+public class FontService : IFontService
+{
+    private readonly IOptionsMonitor<FontConfiguration> _fontConfiguration;
+    
+    private readonly BehaviorSubject<string?> _mainFont = new(null);
+    public IObservable<string?> MainFont => _mainFont.DistinctUntilChanged();
+
+    public FontService(IOptionsMonitor<FontConfiguration> fontConfiguration)
+    {
+        _fontConfiguration = fontConfiguration;
+        fontConfiguration.OnChange(UpdateFonts);
+        
+        UpdateFonts(fontConfiguration.CurrentValue, null);
+    }
+
+    private void UpdateFonts(FontConfiguration newConfiguration, string? arg2)
+    {
+        _mainFont.OnNext(GetMainFont());
+    }
+
+    public string? GetMainFont()
+    {
+        var installedFonts = FontManager.Current.GetInstalledFontFamilyNames().ToList();
+        return _fontConfiguration.CurrentValue.Main.FirstOrDefault(f => installedFonts.Contains(f));
+    }
+}