U4-11227 - default variations and fallback (wip)

src/Umbraco.Core/Models/PublishedContent/ThreadCulturePublishedVariationContextAccessor.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Concurrent;
+using System.Threading;
+
+namespace Umbraco.Core.Models.PublishedContent
+{
+    /// <summary>
+    /// Provides a CurrentUICulture-based implementation of <see cref="IPublishedVariationContextAccessor"/>.
+    /// </summary>
+    /// <remarks>
+    /// <para>This accessor does not support segments. There is no need to set the current context.</para>
+    /// </remarks>
+    public class ThreadCulturePublishedVariationContextAccessor : IPublishedVariationContextAccessor
+    {
+        private readonly ConcurrentDictionary<string, PublishedVariationContext> _contexts = new ConcurrentDictionary<string, PublishedVariationContext>();
+
+        public PublishedVariationContext Context
+        {
+            get => _contexts.GetOrAdd(Thread.CurrentThread.CurrentUICulture.Name, culture => new PublishedVariationContext { Culture = culture });
+            set => throw new NotSupportedException();
+        }
+    }
+}