add log

src/modules/fancyzones/FancyZonesCLI/Commands/LayoutCommands.cs

@@ -142,6 +142,8 @@ internal static class LayoutCommands
 
     public static (int ExitCode, string Output) SetLayout(string[] args, Action<uint> notifyFancyZones, uint wmPrivAppliedLayoutsFileUpdate)
     {
+        Logger.LogInfo($"SetLayout called with args: [{string.Join(", ", args)}]");
+
         if (args.Length == 0)
         {
             return (1, "Error: set-layout requires a UUID parameter");
@@ -251,9 +253,11 @@ internal static class LayoutCommands
 
         // Write back to file
         FancyZonesData.WriteAppliedLayouts(appliedLayouts);
+        Logger.LogInfo($"Applied layouts file updated for {monitorsToUpdate.Count} monitor(s)");
 
         // Notify FancyZones to reload
         notifyFancyZones(wmPrivAppliedLayoutsFileUpdate);
+        Logger.LogInfo("FancyZones notified of layout change");
 
         string layoutName = targetCustomLayout?.Name ?? targetTemplate?.Type ?? uuid;
         if (applyToAll)

src/modules/fancyzones/FancyZonesCLI/FancyZonesData.cs

@@ -84,9 +84,12 @@ internal static class FancyZonesData
         result = null;
         error = null;
 
+        Logger.LogDebug($"Reading file: {filePath}");
+
         if (!File.Exists(filePath))
         {
             error = $"File not found: {Path.GetFileName(filePath)}";
+            Logger.LogWarning(error);
             return false;
         }
 
@@ -97,19 +100,23 @@ internal static class FancyZonesData
             if (result == null)
             {
                 error = $"Failed to parse {Path.GetFileName(filePath)}";
+                Logger.LogError(error);
                 return false;
             }
 
+            Logger.LogDebug($"Successfully read {Path.GetFileName(filePath)}");
             return true;
         }
         catch (JsonException ex)
         {
             error = $"JSON parse error in {Path.GetFileName(filePath)}: {ex.Message}";
+            Logger.LogError(error, ex);
             return false;
         }
         catch (IOException ex)
         {
             error = $"Failed to read {Path.GetFileName(filePath)}: {ex.Message}";
+            Logger.LogError(error, ex);
             return false;
         }
     }
@@ -127,7 +134,9 @@ internal static class FancyZonesData
 
     private static void WriteJsonFile<T>(string filePath, T data, JsonTypeInfo<T> jsonTypeInfo)
     {
+        Logger.LogDebug($"Writing file: {filePath}");
         var json = JsonSerializer.Serialize(data, jsonTypeInfo);
         File.WriteAllText(filePath, json);
+        Logger.LogInfo($"Successfully wrote {Path.GetFileName(filePath)}");
     }
 }

src/modules/fancyzones/FancyZonesCLI/Logger.cs

@@ -0,0 +1,126 @@
+// 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.Globalization;
+using System.IO;
+using System.Runtime.CompilerServices;
+
+namespace FancyZonesCLI;
+
+/// <summary>
+/// Simple logger for FancyZones CLI.
+/// Logs to %LOCALAPPDATA%\Microsoft\PowerToys\FancyZones\CLI\Logs
+/// </summary>
+internal static class Logger
+{
+    private static readonly object LockObj = new();
+    private static string _logFilePath = string.Empty;
+    private static bool _isInitialized;
+
+    /// <summary>
+    /// Gets the path to the current log file.
+    /// </summary>
+    public static string LogFilePath => _logFilePath;
+
+    /// <summary>
+    /// Initializes the logger.
+    /// </summary>
+    public static void InitializeLogger()
+    {
+        if (_isInitialized)
+        {
+            return;
+        }
+
+        try
+        {
+            var localAppData = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
+            var logDirectory = Path.Combine(localAppData, "Microsoft", "PowerToys", "FancyZones", "CLI", "Logs");
+
+            if (!Directory.Exists(logDirectory))
+            {
+                Directory.CreateDirectory(logDirectory);
+            }
+
+            var logFileName = $"FancyZonesCLI_{DateTime.Now:yyyy-MM-dd}.log";
+            _logFilePath = Path.Combine(logDirectory, logFileName);
+            _isInitialized = true;
+
+            LogInfo("FancyZones CLI started");
+        }
+        catch
+        {
+            // Silently fail if logging cannot be initialized
+        }
+    }
+
+    /// <summary>
+    /// Logs an error message.
+    /// </summary>
+    public static void LogError(string message, [CallerMemberName] string memberName = "", [CallerFilePath] string sourceFilePath = "", [CallerLineNumber] int sourceLineNumber = 0)
+    {
+        Log("ERROR", message, memberName, sourceFilePath, sourceLineNumber);
+    }
+
+    /// <summary>
+    /// Logs an error message with exception details.
+    /// </summary>
+    public static void LogError(string message, Exception ex, [CallerMemberName] string memberName = "", [CallerFilePath] string sourceFilePath = "", [CallerLineNumber] int sourceLineNumber = 0)
+    {
+        var fullMessage = ex == null
+            ? message
+            : $"{message} | Exception: {ex.GetType().Name}: {ex.Message}";
+        Log("ERROR", fullMessage, memberName, sourceFilePath, sourceLineNumber);
+    }
+
+    /// <summary>
+    /// Logs a warning message.
+    /// </summary>
+    public static void LogWarning(string message, [CallerMemberName] string memberName = "", [CallerFilePath] string sourceFilePath = "", [CallerLineNumber] int sourceLineNumber = 0)
+    {
+        Log("WARN", message, memberName, sourceFilePath, sourceLineNumber);
+    }
+
+    /// <summary>
+    /// Logs an informational message.
+    /// </summary>
+    public static void LogInfo(string message, [CallerMemberName] string memberName = "", [CallerFilePath] string sourceFilePath = "", [CallerLineNumber] int sourceLineNumber = 0)
+    {
+        Log("INFO", message, memberName, sourceFilePath, sourceLineNumber);
+    }
+
+    /// <summary>
+    /// Logs a debug message (only in DEBUG builds).
+    /// </summary>
+    [System.Diagnostics.Conditional("DEBUG")]
+    public static void LogDebug(string message, [CallerMemberName] string memberName = "", [CallerFilePath] string sourceFilePath = "", [CallerLineNumber] int sourceLineNumber = 0)
+    {
+        Log("DEBUG", message, memberName, sourceFilePath, sourceLineNumber);
+    }
+
+    private static void Log(string level, string message, string memberName, string sourceFilePath, int sourceLineNumber)
+    {
+        if (!_isInitialized || string.IsNullOrEmpty(_logFilePath))
+        {
+            return;
+        }
+
+        try
+        {
+            var fileName = Path.GetFileName(sourceFilePath);
+            var timestamp = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss.fff", CultureInfo.InvariantCulture);
+            var logEntry = $"[{timestamp}] [{level}] [{fileName}:{sourceLineNumber}] [{memberName}] {message}{Environment.NewLine}";
+
+            lock (LockObj)
+            {
+                File.AppendAllText(_logFilePath, logEntry);
+            }
+        }
+        catch
+        {
+            // Silently fail if logging fails
+        }
+    }
+}

src/modules/fancyzones/FancyZonesCLI/Program.cs

@@ -13,6 +13,10 @@ internal sealed class Program
 {
     private static int Main(string[] args)
     {
+        // Initialize logger
+        Logger.InitializeLogger();
+        Logger.LogInfo($"CLI invoked with args: [{string.Join(", ", args)}]");
+
         // Initialize Windows messages
         NativeMethods.InitializeWindowMessages();
 
@@ -48,6 +52,16 @@ internal sealed class Program
             };
         }
 
+        // Log result
+        if (result.ExitCode == 0)
+        {
+            Logger.LogInfo($"Command completed successfully");
+        }
+        else
+        {
+            Logger.LogWarning($"Command failed with exit code {result.ExitCode}: {result.Output}");
+        }
+
         // Output result
         if (!string.IsNullOrEmpty(result.Output))
         {