feat(linux): add graphical platform services

src/AcDream.Headless/Platform/HeadlessPathSet.cs

@@ -1,4 +1,5 @@
 using AcDream.Headless.Configuration;
+using AcDream.Runtime.Platform;
 
 namespace AcDream.Headless.Platform;
 
@@ -14,86 +15,24 @@ internal sealed record HeadlessPathSet(
         ArgumentNullException.ThrowIfNull(overrides);
         platform ??= HeadlessPlatformEnvironment.Instance;
 
-        string config;
-        string data;
-        string cache;
-        if (platform.IsWindows)
+        try
         {
-            string roaming = RequireFolder(
-                platform,
-                Environment.SpecialFolder.ApplicationData);
-            string local = RequireFolder(
-                platform,
-                Environment.SpecialFolder.LocalApplicationData);
-            config = Path.Combine(roaming, "acdream");
-            data = Path.Combine(local, "acdream");
-            cache = Path.Combine(local, "acdream", "cache");
+            ApplicationPathSet paths = ApplicationPathSet.Resolve(
+                overrides.ConfigDirectory,
+                overrides.DataDirectory,
+                overrides.CacheDirectory,
+                platform);
+            return new HeadlessPathSet(
+                paths.ConfigDirectory,
+                paths.DataDirectory,
+                paths.CacheDirectory);
         }
-        else
+        catch (Exception exception)
+            when (exception is ArgumentException
+                or InvalidOperationException
+                or NotSupportedException)
         {
-            string home = RequireFolder(
-                platform,
-                Environment.SpecialFolder.UserProfile);
-            config = ResolveXdg(
-                platform,
-                "XDG_CONFIG_HOME",
-                Path.Combine(home, ".config"),
-                "acdream");
-            data = ResolveXdg(
-                platform,
-                "XDG_DATA_HOME",
-                Path.Combine(home, ".local", "share"),
-                "acdream");
-            cache = ResolveXdg(
-                platform,
-                "XDG_CACHE_HOME",
-                Path.Combine(home, ".cache"),
-                "acdream");
+            throw new HeadlessConfigurationException(exception.Message);
         }
-
-        return new HeadlessPathSet(
-            Normalize(overrides.ConfigDirectory ?? config, platform),
-            Normalize(overrides.DataDirectory ?? data, platform),
-            Normalize(overrides.CacheDirectory ?? cache, platform));
-    }
-
-    private static string ResolveXdg(
-        IHeadlessPlatformEnvironment platform,
-        string variable,
-        string fallback,
-        string leaf)
-    {
-        string? configured = platform.GetEnvironmentVariable(variable);
-        string root = string.IsNullOrWhiteSpace(configured)
-            ? fallback
-            : configured;
-        return Path.Combine(root, leaf);
-    }
-
-    private static string RequireFolder(
-        IHeadlessPlatformEnvironment platform,
-        Environment.SpecialFolder folder)
-    {
-        string value = platform.GetFolderPath(folder);
-        if (string.IsNullOrWhiteSpace(value))
-        {
-            throw new HeadlessConfigurationException(
-                $"The operating system did not provide {folder}.");
-        }
-        return value;
-    }
-
-    private static string Normalize(
-        string path,
-        IHeadlessPlatformEnvironment platform)
-    {
-        if (string.IsNullOrWhiteSpace(path))
-        {
-            throw new HeadlessConfigurationException(
-                "Headless directories cannot be empty.");
-        }
-
-        return Path.TrimEndingDirectorySeparator(
-            Path.GetFullPath(path, platform.CurrentDirectory));
     }
 }

src/AcDream.Headless/Platform/HeadlessPlatformEnvironment.cs

@@ -1,11 +1,10 @@
+using AcDream.Runtime.Platform;
+
 namespace AcDream.Headless.Platform;
 
 internal interface IHeadlessPlatformEnvironment
+    : IApplicationPathEnvironment
 {
-    bool IsWindows { get; }
-    string CurrentDirectory { get; }
-    string? GetEnvironmentVariable(string name);
-    string GetFolderPath(Environment.SpecialFolder folder);
 }
 
 internal sealed class HeadlessPlatformEnvironment