Refactor LightSwitch integration: decouple event handling

Removed LightSwitchListener and ThemeChangedEventArgs. Added LightSwitchService to centralize theme/profile logic. Updated event registration and MainViewModel to handle LightSwitch theme changes via service, decoupling event listening from profile application. Event listening now handled externally.

src/modules/powerdisplay/PowerDisplay.Lib/Services/LightSwitchService.cs

@@ -0,0 +1,112 @@
+// 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.IO;
+using System.Text.Json;
+using ManagedCommon;
+
+namespace PowerDisplay.Common.Services
+{
+    /// <summary>
+    /// Service for handling LightSwitch theme change events.
+    /// Provides methods to process theme changes and read LightSwitch settings.
+    /// Event listening is handled externally via NativeEventWaiter.
+    /// </summary>
+    public static class LightSwitchService
+    {
+        private const string LogPrefix = "[LightSwitch]";
+
+        /// <summary>
+        /// Process a theme change event and return the profile name to apply.
+        /// </summary>
+        /// <param name="isLightMode">Whether the theme changed to light mode.</param>
+        /// <returns>The profile name to apply, or null if no profile is configured.</returns>
+        public static string? GetProfileForTheme(bool isLightMode)
+        {
+            try
+            {
+                Logger.LogInfo($"{LogPrefix} Processing theme change to {(isLightMode ? "light" : "dark")} mode");
+
+                var profileToApply = ReadProfileFromLightSwitchSettings(isLightMode);
+
+                if (string.IsNullOrEmpty(profileToApply) || profileToApply == "(None)")
+                {
+                    Logger.LogInfo($"{LogPrefix} No profile configured for {(isLightMode ? "light" : "dark")} mode");
+                    return null;
+                }
+
+                Logger.LogInfo($"{LogPrefix} Profile to apply: {profileToApply}");
+                return profileToApply;
+            }
+            catch (Exception ex)
+            {
+                Logger.LogError($"{LogPrefix} Failed to process theme change: {ex.Message}");
+                return null;
+            }
+        }
+
+        /// <summary>
+        /// Reads LightSwitch settings and returns the profile name to apply for the given theme.
+        /// </summary>
+        /// <param name="isLightMode">Whether the theme is light mode.</param>
+        /// <returns>The profile name to apply, or null if not configured.</returns>
+        private static string? ReadProfileFromLightSwitchSettings(bool isLightMode)
+        {
+            var settingsPath = PathConstants.LightSwitchSettingsFilePath;
+
+            if (!File.Exists(settingsPath))
+            {
+                Logger.LogWarning($"{LogPrefix} LightSwitch settings file not found");
+                return null;
+            }
+
+            var json = File.ReadAllText(settingsPath);
+            var settings = JsonDocument.Parse(json);
+            var root = settings.RootElement;
+
+            if (!root.TryGetProperty("properties", out var properties))
+            {
+                Logger.LogWarning($"{LogPrefix} LightSwitch settings has no properties");
+                return null;
+            }
+
+            // Check if monitor settings integration is enabled
+            if (!properties.TryGetProperty("apply_monitor_settings", out var applyMonitorSettingsElement) ||
+                !applyMonitorSettingsElement.TryGetProperty("value", out var applyValue) ||
+                !applyValue.GetBoolean())
+            {
+                Logger.LogInfo($"{LogPrefix} Monitor settings integration is disabled");
+                return null;
+            }
+
+            // Get the appropriate profile name based on the theme
+            if (isLightMode)
+            {
+                return GetProfileFromSettings(properties, "enable_light_mode_profile", "light_mode_profile");
+            }
+            else
+            {
+                return GetProfileFromSettings(properties, "enable_dark_mode_profile", "dark_mode_profile");
+            }
+        }
+
+        private static string? GetProfileFromSettings(
+            JsonElement properties,
+            string enableKey,
+            string profileKey)
+        {
+            if (properties.TryGetProperty(enableKey, out var enableElement) &&
+                enableElement.TryGetProperty("value", out var enableValue) &&
+                enableValue.GetBoolean() &&
+                properties.TryGetProperty(profileKey, out var profileElement) &&
+                profileElement.TryGetProperty("value", out var profileValue))
+            {
+                return profileValue.GetString();
+            }
+
+            return null;
+        }
+    }
+}