Initial split of the modules

NadekoBot.Core/Modules/Permissions/Common/PermissionsCollection.cs

@@ -0,0 +1,74 @@
+using System;
+using System.Collections.Generic;
+using NadekoBot.Common.Collections;
+using NadekoBot.Services.Database.Models;
+
+namespace NadekoBot.Modules.Permissions.Common
+{
+    public class PermissionsCollection<T> : IndexedCollection<T> where T : class, IIndexed
+    {
+        private readonly object _localLocker = new object();
+        public PermissionsCollection(IEnumerable<T> source) : base(source)
+        {
+        }
+
+        public static implicit operator List<T>(PermissionsCollection<T> x) => 
+            x.Source;
+
+        public override void Clear()
+        {
+            lock (_localLocker)
+            {
+                var first = Source[0];
+                base.Clear();
+                Source[0] = first;
+            }
+        }
+
+        public override bool Remove(T item)
+        {
+            bool removed;
+            lock (_localLocker)
+            {
+                if(Source.IndexOf(item) == 0)
+                    throw new ArgumentException("You can't remove first permsission (allow all)");
+                removed = base.Remove(item);
+            }
+            return removed;
+        }
+
+        public override void Insert(int index, T item)
+        {
+            lock (_localLocker)
+            {
+                if(index == 0) // can't insert on first place. Last item is always allow all.
+                    throw new IndexOutOfRangeException(nameof(index));
+                base.Insert(index, item);
+            }
+        }
+
+        public override void RemoveAt(int index)
+        {
+            lock (_localLocker)
+            {
+                if(index == 0) // you can't remove first permission (allow all)
+                    throw new IndexOutOfRangeException(nameof(index));
+
+                base.RemoveAt(index);
+            }
+        }
+
+        public override T this[int index] {
+            get => Source[index];
+            set {
+                lock (_localLocker)
+                {
+                    if(index == 0) // can't set first element. It's always allow all
+                        throw new IndexOutOfRangeException(nameof(index));
+                    base[index] = value;
+                }
+            }
+        }
+    }
+
+}