1 files changed, 58 insertions, 0 deletions
diff --git a/src/SMAPI/Framework/SnapshotListDiff.cs b/src/SMAPI/Framework/SnapshotListDiff.cs
new file mode 100644
index 00000000..d4d5df50
--- /dev/null
+++ b/src/SMAPI/Framework/SnapshotListDiff.cs
@@ -0,0 +1,58 @@
+using System.Collections.Generic;
+using StardewModdingAPI.Framework.StateTracking;
+
+namespace StardewModdingAPI.Framework
+{
+    /// <summary>A snapshot of a tracked list.</summary>
+    /// <typeparam name="T">The tracked list value type.</typeparam>
+    internal class SnapshotListDiff<T>
+    {
+        /*********
+        ** Fields
+        *********/
+        /// <summary>The removed values.</summary>
+        private readonly List<T> RemovedImpl = new List<T>();
+
+        /// <summary>The added values.</summary>
+        private readonly List<T> AddedImpl = new List<T>();
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>Whether the value changed since the last update.</summary>
+        public bool IsChanged { get; private set; }
+
+        /// <summary>The removed values.</summary>
+        public IEnumerable<T> Removed => this.RemovedImpl;
+
+        /// <summary>The added values.</summary>
+        public IEnumerable<T> Added => this.AddedImpl;
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Update the snapshot.</summary>
+        /// <param name="isChanged">Whether the value changed since the last update.</param>
+        /// <param name="removed">The removed values.</param>
+        /// <param name="added">The added values.</param>
+        public void Update(bool isChanged, IEnumerable<T> removed, IEnumerable<T> added)
+        {
+            this.IsChanged = isChanged;
+
+            this.RemovedImpl.Clear();
+            this.RemovedImpl.AddRange(removed);
+
+            this.AddedImpl.Clear();
+            this.AddedImpl.AddRange(added);
+        }
+
+        /// <summary>Update the snapshot.</summary>
+        /// <param name="watcher">The value watcher to snapshot.</param>
+        public void Update(ICollectionWatcher<T> watcher)
+        {
+            this.Update(watcher.IsChanged, watcher.Removed, watcher.Added);
+        }
+    }
+}