From ee7765dfe8a82f5843d09cd12cd464e93adb4f4e Mon Sep 17 00:00:00 2001
From: Michael Lamers <devmil@posteo.de>
Date: Sat, 21 Jul 2018 18:17:06 +0200
Subject: [PATCH] ObjectTagger for creating unique object ids

---
 src/net/Qml.Net/Internal/ObjectTagger.cs | 106 +++++++++++++++++++++++
 1 file changed, 106 insertions(+)
 create mode 100644 src/net/Qml.Net/Internal/ObjectTagger.cs

diff --git a/src/net/Qml.Net/Internal/ObjectTagger.cs b/src/net/Qml.Net/Internal/ObjectTagger.cs
new file mode 100644
index 00000000..ad33e1d9
--- /dev/null
+++ b/src/net/Qml.Net/Internal/ObjectTagger.cs
@@ -0,0 +1,106 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+using System.Text;
+
+namespace Qml.Net.Internal
+{
+    public class ObjectId : IDisposable
+    {
+        public ObjectId()
+            : this(0)
+        {
+        }
+
+        private ObjectId(ulong id)
+        {
+            Id = id;
+        }
+
+        public ulong Id { get; private set; }
+
+        public static implicit operator ulong(ObjectId oId)
+        {
+            return oId.Id;
+        }
+
+        public static ObjectId CreateNew()
+        {
+            return new ObjectId(TakeNextFreeId());
+        }
+
+        #region Id management
+
+        private static ulong NextId = 1;
+        private static HashSet<ulong> UsedIds = new HashSet<ulong>();
+
+        private static ulong TakeNextFreeId()
+        {
+            ulong nextId = NextId;
+            UsedIds.Add(nextId);
+            NextId = CalculateNextFreeId(nextId);
+            return nextId;
+        }
+
+        private static ulong CalculateNextFreeId(ulong nextId)
+        {
+            bool firstPass = true;
+            while (UsedIds.Contains(nextId))
+            {
+                if(nextId == ulong.MaxValue)
+                {
+                    if(!firstPass)
+                    {
+                        throw new Exception("Too many object ids in use!");
+                    }
+                    nextId = 1;
+                    firstPass = false;
+                }
+                else
+                {
+                    nextId++;
+                }
+            }
+            return nextId;
+        }
+
+        private static void FreeId(ulong id)
+        {
+            UsedIds.Remove(id);
+        }
+
+        public void Dispose()
+        {
+            FreeId(Id);
+        }
+
+        #endregion
+    }
+
+    public static class ObjectTagger
+    {
+        private static readonly ConditionalWeakTable<object, ObjectId> ObjectIdRefs = new ConditionalWeakTable<object, ObjectId>();
+
+        public static ulong GetOrCreateTag(this object obj)
+        {
+            var result = GetTag(obj);
+            if(result.HasValue)
+            {
+                return result.Value;
+            }
+            var newObjId = ObjectId.CreateNew();
+            ObjectIdRefs.Add(obj, newObjId);
+            return newObjId;
+        }
+
+        public static ulong? GetTag(this object obj)
+        {
+            if (ObjectIdRefs.TryGetValue(obj, out var objId))
+            {
+                return objId;
+            }
+            return null;
+        }
+    }
+}