Implement CMD command for ChangeTheme.

Implement CMD command for ChangeTheme.

Requested at #958

Example:
RetroBar.exe -ChangeTheme "Windows XP Blue"

RetroBar/Program.cs

@@ -1,4 +1,8 @@
-using System;
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using System.Text.Json;
 
 namespace RetroBar
 {
@@ -7,6 +11,7 @@ internal sealed class Program
         private const string MutexName = "RetroBar";
         private const int MutexAttempts = 10;
         private const int MutexWaitMs = 1000;
+        private static readonly string settingsFilePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "RetroBar", "settings.json");
 
         private static System.Threading.Mutex _retroBarMutex;
 
@@ -16,21 +21,29 @@ internal sealed class Program
         [STAThread]
         public static int Main(string[] args)
         {
+            // Check if the -ChangeTheme argument is provided
+            if (args.Length > 0 && args[0] == "-ChangeTheme" && args.Length > 1)
+            {
+                string themeName = args[1];
+                ChangeTheme(themeName);
+                return 0; // Exit immediately after processing the command
+            }
+
+            // If no command line argument is given, start the normal RetroBar application
             if (!SingleInstanceCheck())
             {
                 return 1;
             }
 
+            // Proceed with the normal application flow
             App app = new App();
             app.InitializeComponent();
-
             return app.Run();
         }
 
         private static bool GetMutex()
         {
             _retroBarMutex = new System.Threading.Mutex(true, MutexName, out bool ok);
-
             return ok;
         }
 
@@ -52,5 +65,102 @@ private static bool SingleInstanceCheck()
 
             return false;
         }
+
+        // Method to change the theme and update the settings.json file
+        private static void ChangeTheme(string themeName)
+        {
+            // Kill any running instances of retrobar.exe
+            KillRetroBarProcesses();
+
+            // Ensure the folder exists
+            string directoryPath = Path.GetDirectoryName(settingsFilePath);
+            if (!Directory.Exists(directoryPath))
+            {
+                Directory.CreateDirectory(directoryPath);
+            }
+
+            // Check if the settings file exists
+            if (!File.Exists(settingsFilePath))
+            {
+                // If file does nott exist, create a new one with the theme property
+                Dictionary<string, object> initialSettings = new()
+                {
+                    ["Theme"] = themeName
+                };
+                WriteJsonToFile(initialSettings);
+                return;
+            }
+
+            // Read the existing settings.json file
+            try
+            {
+                string jsonContent = File.ReadAllText(settingsFilePath);
+
+                // Parse the existing JSON into a Dictionary
+                Dictionary<string, object> settings = JsonSerializer.Deserialize<Dictionary<string, object>>(jsonContent);
+
+                // Check if the theme property exists and update it
+                if (settings != null)
+                {
+                    if (settings.ContainsKey("Theme"))
+                    {
+                        settings["Theme"] = themeName;
+                    }
+                    else
+                    {
+                        settings.Add("Theme", themeName);
+                    }
+
+                    // Write the updated JSON back to the file
+                    WriteJsonToFile(settings);
+                }
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine($"Error reading or updating settings: {ex.Message}");
+            }
+        }
+
+        private static void WriteJsonToFile(object jsonObject)
+        {
+            try
+            {
+                // Serialize the object to JSON string with indentation
+                string jsonString = JsonSerializer.Serialize(jsonObject, new JsonSerializerOptions { WriteIndented = true });
+
+                // Write the serialized JSON string to the file
+                File.WriteAllText(settingsFilePath, jsonString);
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine($"Error writing to file: {ex.Message}");
+            }
+        }
+
+        private static void KillRetroBarProcesses()
+        {
+            try
+            {
+                // Get the current process ID (this is the one we want to keep running)
+                int currentProcessId = System.Diagnostics.Process.GetCurrentProcess().Id;
+
+                // Get all processes running with the name "retrobar.exe"
+                Process[] processes = System.Diagnostics.Process.GetProcessesByName("retrobar");
+
+                // Iterate over all retrobar.exe processes
+                foreach (var process in processes)
+                {
+                    // Skip the process that is currently running this command
+                    if (process.Id != currentProcessId)
+                    {
+                        process.Kill();
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine($"Error killing processes: {ex.Message}");
+            }
+        }
     }
 }