Add XDG_DATA_HOME as default storage location

src/XIVLauncher.Core/CoreEnvironmentSettings.cs

@@ -17,6 +17,27 @@ public static class CoreEnvironmentSettings
     public static bool IsSteamCompatTool => CheckEnvBool("XL_SCT");
     public static uint SteamAppId => GetAppId(Environment.GetEnvironmentVariable("SteamAppId"));
     public static uint AltAppID => GetAppId(Environment.GetEnvironmentVariable("XL_APPID"));
+
+    private static string? userDir = null;
+    public static string UserDir
+    {
+        get
+        {
+            if (userDir != null)
+                return userDir;
+
+            var uDir = Environment.GetEnvironmentVariable("XL_USERDIR") ?? "";
+            var uDir2 = Environment.GetEnvironmentVariable("XL_USER_DIR") ?? "";
+            var xlPath = Environment.GetEnvironmentVariable("XL_PATH") ?? "";
+            if (!string.IsNullOrEmpty(uDir))
+                userDir = uDir;
+            else if (!string.IsNullOrEmpty(uDir2))
+                userDir = uDir2;
+            else
+                userDir = xlPath;
+            return userDir;
+        }
+    }
 
     private static bool CheckEnvBool(string key)
     {

src/XIVLauncher.Core/Program.cs

@@ -181,7 +181,9 @@ private static DalamudUpdater CreateDalamudUpdater()
     private static void Main(string[] args)
     {
         mainArgs = args;
-        storage = new Storage(APP_NAME);
+        // XDG will handle the storage path for Linux and Mac. It will fall back to the old ~/.xlcore path on Linux and Mac if it exists and the XDG path does not.
+        var userDir = XDG.GetStoragePath(APP_NAME, CoreEnvironmentSettings.UserDir);
+        storage = new Storage(APP_NAME, userDir);
 
         if (CoreEnvironmentSettings.ClearAll)
         {

src/XIVLauncher.Core/XDG.cs

@@ -0,0 +1,59 @@
+using System.IO;
+
+using XIVLauncher.Common;
+
+namespace XIVLauncher.Core;
+
+public static class XDG
+{
+    private static Platform platform;
+
+    static XDG()
+    {
+        if (Environment.OSVersion.Platform == PlatformID.Win32NT)
+        {
+            platform = Platform.Win32;
+        }
+        else if (Environment.OSVersion.Platform == PlatformID.Unix)
+        {
+            platform = Platform.Linux;
+        }
+        else if (Environment.OSVersion.Platform == PlatformID.MacOSX)
+        {
+            platform = Platform.Mac;
+        }
+        else
+        {
+            throw new PlatformNotSupportedException("Unsupported platform");
+        }
+    }
+    public static string? GetStoragePath(string appName, string? overridePath = null)
+    {
+        if (!string.IsNullOrEmpty(overridePath))
+        {
+            return overridePath;
+        }
+        if (platform == Platform.Win32)
+        {
+            return null; // Let Storage class handle it. Windows works fine.
+        }
+        else if (platform == Platform.Linux  || platform == Platform.Mac)
+        {
+            if (Directory.Exists(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), appName)))
+            {
+                return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), appName); // Use XDG Base Directory spec path if it exists.
+                                                                                                                         // This is ~/.local/share/xlcore on Linux and ~/Library/Application Support/xlcore on Mac.
+                                                                                                                         // This can be overridden with the XL_USERDIR environment variable, which will take precedence over both the old path and the XDG path.
+            }
+            if (Directory.Exists(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.UserProfile), $".{appName}")))
+            {
+                return null; // Let Storage class handle it and use the old ~/.xlcore path if it exists, and the XDG_DATA_HOME/xlcore directory does not exist.
+            }
+            return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), appName); // Use XDG Base Directory spec path for new installs on Linux and Mac.
+        }
+        else
+        {
+            throw new PlatformNotSupportedException("Unsupported platform");
+        }
+    }
+}