rewrite world/player state tracking (#453)

1 files changed, 86 insertions, 0 deletions

diff --git a/src/SMAPI/Framework/StateTracking/FieldWatchers/ObservableCollectionWatcher.cs b/src/SMAPI/Framework/StateTracking/FieldWatchers/ObservableCollectionWatcher.cs
new file mode 100644
index 00000000..34a97097
--- /dev/null
+++ b/src/SMAPI/Framework/StateTracking/FieldWatchers/ObservableCollectionWatcher.cs
@@ -0,0 +1,86 @@
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Collections.Specialized;
+using System.Linq;
+
+namespace StardewModdingAPI.Framework.StateTracking.FieldWatchers
+{
+    /// <summary>A watcher which detects changes to an observable collection.</summary>
+    internal class ObservableCollectionWatcher<TValue> : BaseDisposableWatcher, ICollectionWatcher<TValue>
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The field being watched.</summary>
+        private readonly ObservableCollection<TValue> Field;
+
+        /// <summary>The pairs added since the last reset.</summary>
+        private readonly List<TValue> AddedImpl = new List<TValue>();
+
+        /// <summary>The pairs demoved since the last reset.</summary>
+        private readonly List<TValue> RemovedImpl = new List<TValue>();
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>Whether the collection changed since the last reset.</summary>
+        public bool IsChanged => this.AddedImpl.Count > 0 || this.RemovedImpl.Count > 0;
+
+        /// <summary>The values added since the last reset.</summary>
+        public IEnumerable<TValue> Added => this.AddedImpl;
+
+        /// <summary>The values removed since the last reset.</summary>
+        public IEnumerable<TValue> Removed => this.RemovedImpl;
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="field">The field to watch.</param>
+        public ObservableCollectionWatcher(ObservableCollection<TValue> field)
+        {
+            this.Field = field;
+            field.CollectionChanged += this.OnCollectionChanged;
+        }
+
+        /// <summary>Update the current value if needed.</summary>
+        public void Update()
+        {
+            this.AssertNotDisposed();
+        }
+
+        /// <summary>Set the current value as the baseline.</summary>
+        public void Reset()
+        {
+            this.AssertNotDisposed();
+
+            this.AddedImpl.Clear();
+            this.RemovedImpl.Clear();
+        }
+
+        /// <summary>Stop watching the field and release all references.</summary>
+        public override void Dispose()
+        {
+            if (!this.IsDisposed)
+                this.Field.CollectionChanged -= this.OnCollectionChanged;
+            base.Dispose();
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>A callback invoked when an entry is added or removed from the collection.</summary>
+        /// <param name="sender">The event sender.</param>
+        /// <param name="e">The event arguments.</param>
+        private void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
+        {
+            if (e.NewItems != null)
+                this.AddedImpl.AddRange(e.NewItems.Cast<TValue>());
+            if (e.OldItems != null)
+                this.RemovedImpl.AddRange(e.OldItems.Cast<TValue>());
+        }
+    }
+}