1 files changed, 100 insertions, 0 deletions
diff --git a/src/SMAPI/Framework/StateTracking/FieldWatchers/NetListWatcher.cs b/src/SMAPI/Framework/StateTracking/FieldWatchers/NetListWatcher.cs
new file mode 100644
index 00000000..cac66356
--- /dev/null
+++ b/src/SMAPI/Framework/StateTracking/FieldWatchers/NetListWatcher.cs
@@ -0,0 +1,100 @@
+using System;
+using System.Collections.Generic;
+using Netcode;
+
+namespace StardewModdingAPI.Framework.StateTracking.FieldWatchers
+{
+    internal class NetListWatcher<TKey, TValue> : BaseDisposableWatcher, ICollectionWatcher<TValue>
+        where TValue : class, INetObject<INetSerializable>
+    {
+
+
+        /*********
+        ** Fields
+        *********/
+        /// <summary>The field being watched.</summary>
+        private readonly NetList<TValue, Netcode.NetRef<TValue>> Field;
+
+        public TKey Key { get; }
+
+        /// <summary>The pairs added since the last reset.</summary>
+        private readonly IList<TValue> AddedImpl = new List<TValue>();
+
+        /// <summary>The pairs removed since the last reset.</summary>
+        private readonly IList<TValue> RemovedImpl = new List<TValue>();
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="field">The field to watch.</param>
+        public NetListWatcher(NetList<TValue, Netcode.NetRef<TValue>> field, TKey key)
+        {
+            this.Field = field;
+            this.Key = key;
+            field.OnElementChanged += this.OnElementChanged;
+            field.OnArrayReplaced += this.OnArrayReplaced;
+        }
+
+        public bool IsChanged => this.AddedImpl.Count > 0 || this.RemovedImpl.Count > 0;
+
+        public IEnumerable<TValue> Added => this.AddedImpl;
+
+        public IEnumerable<TValue> Removed => this.RemovedImpl;
+
+        public void Dispose()
+        {
+            if (!this.IsDisposed)
+            {
+                this.Field.OnElementChanged -= this.OnElementChanged;
+                this.Field.OnArrayReplaced -= this.OnArrayReplaced;
+            }
+
+            base.Dispose();
+        }
+
+        public void Reset()
+        {
+            this.AddedImpl.Clear();
+            this.RemovedImpl.Clear();
+        }
+
+        public void Update()
+        {
+            this.AssertNotDisposed();
+        }
+
+        /*********
+        ** Private methods
+        *********/
+        private void OnArrayReplaced(NetList<TValue, Netcode.NetRef<TValue>> list, IList<TValue> before, IList<TValue> after)
+        {
+            this.AddedImpl.Clear();
+            this.RemovedImpl.Clear();
+
+            foreach(var obj in after)
+                this.AddedImpl.Add(obj);
+
+            foreach(var obj in before)
+                this.RemovedImpl.Add(obj);
+        }
+
+        private void OnElementChanged(NetList<TValue, Netcode.NetRef<TValue>> list, int index, TValue oldValue, TValue newValue)
+        {
+
+            /* checks for stack addition / subtraction changing stacks does not fire off an element changed event
+            if ((oldValue != null && newValue != null) && oldValue.CompareTo(newValue) < 0)
+                this.AddedImpl.Add(newValue);
+            //Stack Removed from
+            if ((oldValue != null && newValue != null) && oldValue.CompareTo(newValue) > 0)
+                this.RemovedImpl.Add(newValue);
+                */
+
+            if(newValue!=null)
+                this.AddedImpl.Add(newValue);
+
+            if(oldValue!=null)
+                this.RemovedImpl.Add(oldValue);
+        }
+    }
+}