[Run] Fix dark mode detection code, plus refactor (#37324)

* Fix risky int cast in dark mode detection.

* Refactored Helper and Manager classes. New unit tests and changes to support Registry access mocking.

* Spelling update.

* Improve documentation for the registry-related classes.

* Fix issue with UpdateTheme raised in review. Enhance documentation. Rewrite tests to use parameterised unit tests, and expand to cover more cases.

src/modules/launcher/Wox.Test/ThemeHelperTest.cs

@@ -0,0 +1,124 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Linq.Expressions;
+using ManagedCommon;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Moq;
+using PowerLauncher.Helper;
+using PowerLauncher.Services;
+
+namespace Wox.Test;
+
+[TestClass]
+public class ThemeHelperTest
+{
+    // Registry key paths.
+    private const string ThemesKey = @"HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Themes";
+    private const string PersonalizeKey = ThemesKey + "\\Personalize";
+
+    // Theme paths.
+    private const string HighContrastThemePath = @"C:\WINDOWS\resources\Ease of Access Themes\hcwhite.theme";
+    private const string NonHighContrastThemePath = @"C:\Users\Test\AppData\Local\Microsoft\Windows\Themes\Custom.theme";
+
+    /// <summary>
+    /// The expected High Contrast theme when the <see cref="HighContrastThemePath"/> is returned
+    /// from the registry.
+    /// </summary>
+    private const Theme HighContrastTheme = Theme.HighContrastWhite;
+
+    /// <summary>
+    /// Mock <see cref="IRegistryService.GetValue"/>, to return the value of the AppsUseLightTheme
+    /// key.
+    /// </summary>
+    private static readonly Expression<Func<IRegistryService, object>> _mockAppsUseLightTheme = (service) =>
+        service.GetValue(PersonalizeKey, "AppsUseLightTheme", ThemeHelper.AppsUseLightThemeDefault);
+
+    /// <summary>
+    /// Mock <see cref="IRegistryService.GetValue"/> to return the value of the CurrentTheme key.
+    /// </summary>
+    /// <remarks>
+    /// The default value given here - string.Empty - must be the same as the default value in the
+    /// actual code for tests using this mock to be valid.
+    /// </remarks>
+    private static readonly Expression<Func<IRegistryService, object>> _mockCurrentTheme = (service) =>
+        service.GetValue(ThemesKey, "CurrentTheme", string.Empty);
+
+    /// <summary>
+    /// Test GetAppsTheme method.
+    /// </summary>
+    /// <param name="registryValue">The mocked value for the AppsUseLightTheme registry key.</param>
+    /// <param name="expectedTheme">The expected <see cref="Theme"/> output from the call to
+    /// <see cref="ThemeHelper.GetAppsTheme"/>.</param>
+    [DataTestMethod]
+    [DataRow(ThemeHelper.AppsUseLightThemeLight, Theme.Light)]
+    [DataRow(ThemeHelper.AppsUseLightThemeDark, Theme.Dark)]
+    [DataRow(int.MaxValue, Theme.Light)] // Out of range values should default to Light
+    [DataRow(null, Theme.Light)] // Missing keys or values should default to Light
+    [DataRow("RandomString", Theme.Light)] // Invalid string values should default to Light
+    public void GetAppsTheme_ReturnsExpectedTheme(object registryValue, Theme expectedTheme)
+    {
+        var mockService = new Mock<IRegistryService>();
+        mockService.Setup(_mockAppsUseLightTheme).Returns(registryValue);
+
+        var helper = new ThemeHelper(mockService.Object);
+
+        Assert.AreEqual(expectedTheme, helper.GetAppsTheme());
+    }
+
+    /// <summary>
+    /// Test <see cref="ThemeHelper.GetHighContrastTheme"/>.
+    /// </summary>
+    /// <param name="registryValue">The mocked value for the CurrentTheme registry key.</param>
+    /// <param name="expectedTheme">The expected <see cref="Theme"/> output from the call to
+    /// <see cref="ThemeHelper.GetHighContrastTheme"/>.</param>
+    [DataTestMethod]
+    [DataRow(HighContrastThemePath, HighContrastTheme)] // Valid High Contrast theme
+    [DataRow(NonHighContrastThemePath, null)] // Non-High Contrast theme should return null
+    [DataRow(null, null)] // Missing keys or values should default to null
+    [DataRow("", null)] // Empty string values should default to null
+    public void GetHighContrastTheme_ReturnsExpectedTheme(string registryValue, Theme? expectedTheme)
+    {
+        var mockService = new Mock<IRegistryService>();
+        mockService.Setup(_mockCurrentTheme).Returns(registryValue);
+
+        var helper = new ThemeHelper(mockService.Object);
+
+        Assert.AreEqual(expectedTheme, helper.GetHighContrastTheme());
+    }
+
+    /// <summary>
+    /// Test <see cref="ThemeHelper.DetermineTheme"/>.
+    /// </summary>
+    /// <param name="registryTheme">The mocked value for the CurrentTheme registry key.</param>
+    /// <param name="requestedTheme">The <see cref="Theme"/> value from the application's settings.
+    /// </param>
+    /// <param name="expectedTheme">The expected <see cref="Theme"/> output from the call to
+    /// <see cref="ThemeHelper.DetermineTheme"/>.</param>
+    /// <param name="appsUseLightTheme">The mocked value for the AppsUseLightTheme registry key,
+    /// representing the system preference for Light or Dark mode.</param>
+    [DataTestMethod]
+    [DataRow(HighContrastThemePath, Theme.System, HighContrastTheme)] // High Contrast theme active
+    [DataRow(HighContrastThemePath, Theme.Light, HighContrastTheme)] // High Contrast theme active - Light mode override ignored
+    [DataRow(HighContrastThemePath, Theme.Dark, HighContrastTheme)] // High Contrast theme active - Dark mode override ignored
+    [DataRow(NonHighContrastThemePath, Theme.System, Theme.Light)] // System preference with default light theme
+    [DataRow(NonHighContrastThemePath, Theme.System, Theme.Dark, ThemeHelper.AppsUseLightThemeDark)] // System preference with dark mode
+    [DataRow(NonHighContrastThemePath, Theme.Light, Theme.Light, ThemeHelper.AppsUseLightThemeDark)] // Light mode override
+    [DataRow(NonHighContrastThemePath, Theme.Dark, Theme.Dark, ThemeHelper.AppsUseLightThemeLight)] // Dark mode override
+    [DataRow(null, Theme.System, Theme.Light)] // Missing keys or values should default to Light
+    [DataRow("", Theme.System, Theme.Light)] // Empty current theme paths should default to Light
+    [DataRow("RandomString", Theme.System, Theme.Light)] // Invalid current theme paths should default to Light
+    [DataRow(NonHighContrastThemePath, (Theme)int.MaxValue, Theme.Light)] // Invalid theme values should default to Light
+    public void DetermineTheme_ReturnsExpectedTheme(string registryTheme, Theme requestedTheme, Theme expectedTheme, int? appsUseLightTheme = 1)
+    {
+        var mockService = new Mock<IRegistryService>();
+        mockService.Setup(_mockCurrentTheme).Returns(registryTheme);
+        mockService.Setup(_mockAppsUseLightTheme).Returns(appsUseLightTheme);
+
+        var helper = new ThemeHelper(mockService.Object);
+
+        Assert.AreEqual(expectedTheme, helper.DetermineTheme(requestedTheme));
+    }
+}