Resolve service logs under interactive user profile

Resolves %LocalAppData% from the logged-on console user and separates client/backend log folders.

Services/Logging/InteractiveUserPath.cs

@@ -0,0 +1,58 @@
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Text;
+
+namespace UtopiaCanteenSystem.Services.Logging;
+
+/// <summary>
+/// Resolves the logged-on Windows user's profile paths when the app runs as a service (SYSTEM).
+/// </summary>
+internal static class InteractiveUserPath
+{
+    public static string? TryGetLocalAppDataPath()
+    {
+        var profile = TryGetProfileDirectory();
+        if (string.IsNullOrWhiteSpace(profile))
+            return null;
+
+        var localAppData = Path.Combine(profile, "AppData", "Local");
+        return Directory.Exists(localAppData) ? localAppData : null;
+    }
+
+    private static string? TryGetProfileDirectory()
+    {
+        var sessionId = WTSGetActiveConsoleSessionId();
+        if (sessionId == 0xFFFFFFFF)
+            return null;
+
+        if (!WTSQueryUserToken(sessionId, out var userToken) || userToken == IntPtr.Zero)
+            return null;
+
+        try
+        {
+            var sb = new StringBuilder(512);
+            var size = sb.Capacity;
+            if (!GetUserProfileDirectory(userToken, sb, ref size, out _))
+                return null;
+
+            var path = sb.ToString();
+            return string.IsNullOrWhiteSpace(path) ? null : path;
+        }
+        finally
+        {
+            CloseHandle(userToken);
+        }
+    }
+
+    [DllImport("kernel32.dll")]
+    private static extern uint WTSGetActiveConsoleSessionId();
+
+    [DllImport("wtsapi32.dll", SetLastError = true)]
+    private static extern bool WTSQueryUserToken(uint sessionId, out IntPtr phToken);
+
+    [DllImport("userenv.dll", SetLastError = true, CharSet = CharSet.Unicode)]
+    private static extern bool GetUserProfileDirectory(IntPtr hToken, StringBuilder lpProfileDir, ref int lpcchSize, out int lpDwFlags);
+
+    [DllImport("kernel32.dll", SetLastError = true)]
+    private static extern bool CloseHandle(IntPtr hObject);
+}

Services/Logging/LogPaths.cs

@@ -0,0 +1,65 @@
+using System.IO;
+
+namespace UtopiaCanteenSystem.Services.Logging;
+
+/// <summary>
+/// File log directories. Client uses the current user's LocalAppData.
+/// Backend (Windows Service) uses the interactive user's LocalAppData when possible
+/// so logs appear under the logged-on user's profile instead of systemprofile.
+/// </summary>
+public static class LogPaths
+{
+    private static string? _backendLogsDirectoryOverride;
+    private static string? _cachedLocalAppDataRoot;
+
+    /// <summary>
+    /// Optional absolute path (e.g. from appsettings LogsDirectory). Used by the backend service only.
+    /// </summary>
+    public static void SetBackendLogsDirectory(string? directory)
+    {
+        _backendLogsDirectoryOverride = string.IsNullOrWhiteSpace(directory)
+            ? null
+            : directory.Trim();
+    }
+
+    /// <summary>
+    /// Client logs folder: %LocalAppData%\UtopiaCanteenClient\Logs.
+    /// </summary>
+    public static string ClientLogsDirectory =>
+        Path.Combine(ResolveLocalAppDataRoot(), "UtopiaCanteenClient", "Logs");
+
+    /// <summary>
+    /// Backend logs folder: %LocalAppData%\UtopiaCanteenBackend\Logs
+    /// (interactive user when running as a service).
+    /// </summary>
+    public static string BackendLogsDirectory =>
+        _backendLogsDirectoryOverride ?? Path.Combine(ResolveLocalAppDataRoot(), "UtopiaCanteenBackend", "Logs");
+
+    public static string GetBackendLogFilePath(DateTime? date = null)
+    {
+        var d = date ?? DateTime.Now;
+        return Path.Combine(BackendLogsDirectory, $"backend-{d:yyyy-MM-dd}.log");
+    }
+
+    public static string GetClientLogFilePath(DateTime? date = null)
+    {
+        var d = date ?? DateTime.Now;
+        return Path.Combine(ClientLogsDirectory, $"client-{d:yyyy-MM-dd}.log");
+    }
+
+    /// <summary>
+    /// User's LocalAppData, or SYSTEM profile when no interactive session (service at login screen).
+    /// </summary>
+    public static string ResolveLocalAppDataRoot()
+    {
+        if (!string.IsNullOrEmpty(_cachedLocalAppDataRoot))
+            return _cachedLocalAppDataRoot;
+
+        var interactive = InteractiveUserPath.TryGetLocalAppDataPath();
+        if (!string.IsNullOrWhiteSpace(interactive))
+            return _cachedLocalAppDataRoot = interactive;
+
+        return _cachedLocalAppDataRoot =
+            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
+    }
+}