(GH-3623) ThemeManager: Introduce ThemeType

This enumeration helps us to check for light and dark themes.

src/MahApps.Metro/ThemeManager/Theme.cs

@@ -64,6 +64,14 @@ public Theme([NotNull] ResourceDictionary resourceDictionary)
             this.BaseColorScheme = (string)this.Resources[ThemeBaseColorSchemeKey];
             this.ColorScheme = (string)this.Resources[ThemeColorSchemeKey];
             this.ShowcaseBrush = (SolidColorBrush)this.Resources[ThemeShowcaseBrushKey];
+            if (this.Name.StartsWith("light.", StringComparison.OrdinalIgnoreCase))
+            {
+                this.Type = ThemeType.Light;
+            }
+            else if (this.Name.StartsWith("dark.", StringComparison.OrdinalIgnoreCase))
+            {
+                this.Type = ThemeType.Dark;
+            }
         }
 
         /// <summary>
@@ -76,6 +84,11 @@ public Theme([NotNull] ResourceDictionary resourceDictionary)
         /// </summary>
         public string Name { get; }
 
+        /// <summary>
+        /// Gets the theme type (light, dark).
+        /// </summary>
+        public ThemeType Type { get; } = ThemeType.Unknown;
+
         /// <summary>
         /// Gets the display name of the theme.
         /// </summary>

src/MahApps.Metro/ThemeManager/ThemeManager.cs

@@ -324,12 +324,12 @@ public static Theme GetInverseTheme([NotNull] Theme theme)
                 throw new ArgumentNullException(nameof(theme));
             }
 
-            if (theme.Name.StartsWith("dark.", StringComparison.OrdinalIgnoreCase))
+            if (theme.Type == ThemeType.Dark)
             {
                 return GetTheme("Light." + theme.Name.Substring("dark.".Length));
             }
 
-            if (theme.Name.StartsWith("light.", StringComparison.OrdinalIgnoreCase))
+            if (theme.Type == ThemeType.Light)
             {
                 return GetTheme("Dark." + theme.Name.Substring("light.".Length));
             }

src/MahApps.Metro/ThemeManager/ThemeType.cs

@@ -0,0 +1,12 @@
+namespace MahApps.Metro
+{
+    /// <summary>
+    /// An Enum representing the theme type.
+    /// </summary>
+    public enum ThemeType
+    {
+        Unknown,
+        Light,
+        Dark
+    }
+}