Renamed Umbraco.Abstractions to Umbraco.Core

src/Umbraco.Core/Collections/OrderedHashSet.cs

@@ -0,0 +1,50 @@
+using System.Collections.ObjectModel;
+
+namespace Umbraco.Core.Collections
+{
+    /// <summary>
+    /// A custom collection similar to HashSet{T} which only contains unique items, however this collection keeps items in order
+    /// and is customizable to keep the newest or oldest equatable item
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    public class OrderedHashSet<T> : KeyedCollection<T, T>
+    {
+        private readonly bool _keepOldest;
+
+        public OrderedHashSet(bool keepOldest = true)
+        {
+            _keepOldest = keepOldest;
+        }
+
+        protected override void InsertItem(int index, T item)
+        {
+            if (Dictionary == null)
+            {
+                base.InsertItem(index, item);
+            }
+            else
+            {
+                var exists = Dictionary.ContainsKey(item);
+
+                //if we want to keep the newest, then we need to remove the old item and add the new one
+                if (exists == false)
+                {
+                    base.InsertItem(index, item);
+                }
+                else if(_keepOldest == false)
+                {
+                    if (Remove(item))
+                    {
+                        index--;
+                    }
+                    base.InsertItem(index, item);
+                }
+            }
+        }
+
+        protected override T GetKeyForItem(T item)
+        {
+            return item;
+        }
+    }
+}