Move ItemsProxy sort helpers

src/Jellyfin.Plugin.Multilang/Services/ItemsProxySorting.cs

@@ -1,6 +1,7 @@
 using System.Globalization;
 using System.Text;
 using System.Text.Json.Nodes;
+using Jellyfin.Plugin.Multilang.Configuration;
 
 namespace Jellyfin.Plugin.Multilang.Services;
 
@@ -52,6 +53,57 @@ public static class ItemsProxySorting
         }
     }
 
+    public static string ResolveSortLocale(string? configuredLocale, string? clientLocale)
+    {
+        var configured = (configuredLocale ?? string.Empty).Trim();
+        return configured.Length > 0 && !configured.Equals("Auto", StringComparison.OrdinalIgnoreCase)
+            ? configured
+            : (clientLocale ?? string.Empty).Trim();
+    }
+
+    public static CultureInfo GetSortCulture(string? sortLocale)
+    {
+        var locale = (sortLocale ?? string.Empty).Trim();
+        if (locale.Length == 0)
+            return CultureInfo.InvariantCulture;
+
+        try
+        {
+            return CultureInfo.GetCultureInfo(locale);
+        }
+        catch (CultureNotFoundException)
+        {
+            return CultureInfo.InvariantCulture;
+        }
+    }
+
+    public static string[] GetSortArticles(SortArticleCatalog articleCatalog, IEnumerable<SortArticleEntry> configuredArticles, string? sortLocale)
+    {
+        var locale = (sortLocale ?? string.Empty).Trim();
+        if (locale.Length == 0)
+            locale = "en";
+
+        var configured = configuredArticles.ToArray();
+        var custom = configured.FirstOrDefault(e => e.Language.Equals(locale, StringComparison.OrdinalIgnoreCase))
+                     ?? configured.FirstOrDefault(e => locale.StartsWith(e.Language + "-", StringComparison.OrdinalIgnoreCase));
+        if (custom is not null)
+            return SplitArticles(custom.Articles);
+
+        var builtIns = articleCatalog.GetBuiltIns();
+        if (builtIns.TryGetValue(locale, out var exact))
+            return exact;
+
+        var dash = locale.IndexOf('-', StringComparison.Ordinal);
+        return dash > 0 && builtIns.TryGetValue(locale[..dash], out var languageOnly)
+            ? languageOnly
+            : [];
+    }
+
+    private static string[] SplitArticles(string articles)
+        => articles.Split([',', ';'], StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
+            .Distinct(StringComparer.OrdinalIgnoreCase)
+            .ToArray();
+
     private static bool TryGetItemsArray(JsonNode root, out JsonArray items)
     {
         if (root is JsonObject obj && obj["Items"] is JsonArray array)