add immutable collection watcher

3 files changed, 62 insertions, 15 deletions

diff --git a/src/SMAPI/Framework/StateTracking/FieldWatchers/ImmutableCollectionWatcher.cs b/src/SMAPI/Framework/StateTracking/FieldWatchers/ImmutableCollectionWatcher.cs
new file mode 100644
index 00000000..30e6274f
--- /dev/null
+++ b/src/SMAPI/Framework/StateTracking/FieldWatchers/ImmutableCollectionWatcher.cs
@@ -0,0 +1,37 @@
+using System.Collections.Generic;
+
+namespace StardewModdingAPI.Framework.StateTracking.FieldWatchers
+{
+    /// <summary>A collection watcher which never changes.</summary>
+    /// <typeparam name="TValue">The value type within the collection.</typeparam>
+    internal class ImmutableCollectionWatcher<TValue> : BaseDisposableWatcher, ICollectionWatcher<TValue>
+    {
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>A singleton collection watcher instance.</summary>
+        public static ImmutableCollectionWatcher<TValue> Instance { get; } = new ImmutableCollectionWatcher<TValue>();
+
+        /// <summary>Whether the collection changed since the last reset.</summary>
+        public bool IsChanged { get; } = false;
+
+        /// <summary>The values added since the last reset.</summary>
+        public IEnumerable<TValue> Added { get; } = new TValue[0];
+
+        /// <summary>The values removed since the last reset.</summary>
+        public IEnumerable<TValue> Removed { get; } = new TValue[0];
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Update the current value if needed.</summary>
+        public void Update() { }
+
+        /// <summary>Set the current value as the baseline.</summary>
+        public void Reset() { }
+
+        /// <summary>Stop watching the field and release all references.</summary>
+        public override void Dispose() { }
+    }
+}
diff --git a/src/SMAPI/Framework/StateTracking/FieldWatchers/WatcherFactory.cs b/src/SMAPI/Framework/StateTracking/FieldWatchers/WatcherFactory.cs
index 8301351e..314ff7f5 100644
--- a/src/SMAPI/Framework/StateTracking/FieldWatchers/WatcherFactory.cs
+++ b/src/SMAPI/Framework/StateTracking/FieldWatchers/WatcherFactory.cs
@@ -12,10 +12,13 @@ namespace StardewModdingAPI.Framework.StateTracking.FieldWatchers
         /*********
         ** Public methods
         *********/
+        /****
+        ** Values
+        ****/
         /// <summary>Get a watcher which compares values using their <see cref="object.Equals(object)"/> method. This method should only be used when <see cref="ForEquatable{T}"/> won't work, since this doesn't validate whether they're comparable.</summary>
         /// <typeparam name="T">The value type.</typeparam>
         /// <param name="getValue">Get the current value.</param>
-        public static ComparableWatcher<T> ForGenericEquality<T>(Func<T> getValue) where T : struct
+        public static IValueWatcher<T> ForGenericEquality<T>(Func<T> getValue) where T : struct
         {
             return new ComparableWatcher<T>(getValue, new GenericEqualsComparer<T>());
         }
@@ -23,7 +26,7 @@ namespace StardewModdingAPI.Framework.StateTracking.FieldWatchers
         /// <summary>Get a watcher for an <see cref="IEquatable{T}"/> value.</summary>
         /// <typeparam name="T">The value type.</typeparam>
         /// <param name="getValue">Get the current value.</param>
-        public static ComparableWatcher<T> ForEquatable<T>(Func<T> getValue) where T : IEquatable<T>
+        public static IValueWatcher<T> ForEquatable<T>(Func<T> getValue) where T : IEquatable<T>
         {
             return new ComparableWatcher<T>(getValue, new EquatableComparer<T>());
         }
@@ -31,15 +34,27 @@ namespace StardewModdingAPI.Framework.StateTracking.FieldWatchers
         /// <summary>Get a watcher which detects when an object reference changes.</summary>
         /// <typeparam name="T">The value type.</typeparam>
         /// <param name="getValue">Get the current value.</param>
-        public static ComparableWatcher<T> ForReference<T>(Func<T> getValue)
+        public static IValueWatcher<T> ForReference<T>(Func<T> getValue)
         {
             return new ComparableWatcher<T>(getValue, new ObjectReferenceComparer<T>());
         }
 
+        /// <summary>Get a watcher for a net collection.</summary>
+        /// <typeparam name="T">The value type.</typeparam>
+        /// <typeparam name="TSelf">The net field instance type.</typeparam>
+        /// <param name="field">The net collection.</param>
+        public static IValueWatcher<T> ForNetValue<T, TSelf>(NetFieldBase<T, TSelf> field) where TSelf : NetFieldBase<T, TSelf>
+        {
+            return new NetValueWatcher<T, TSelf>(field);
+        }
+
+        /****
+        ** Collections
+        ****/
         /// <summary>Get a watcher which detects when an object reference in a collection changes.</summary>
         /// <typeparam name="T">The value type.</typeparam>
         /// <param name="collection">The observable collection.</param>
-        public static ComparableListWatcher<T> ForReferenceList<T>(ICollection<T> collection)
+        public static ICollectionWatcher<T> ForReferenceList<T>(ICollection<T> collection)
         {
             return new ComparableListWatcher<T>(collection, new ObjectReferenceComparer<T>());
         }
@@ -47,24 +62,22 @@ namespace StardewModdingAPI.Framework.StateTracking.FieldWatchers
         /// <summary>Get a watcher for an observable collection.</summary>
         /// <typeparam name="T">The value type.</typeparam>
         /// <param name="collection">The observable collection.</param>
-        public static ObservableCollectionWatcher<T> ForObservableCollection<T>(ObservableCollection<T> collection)
+        public static ICollectionWatcher<T> ForObservableCollection<T>(ObservableCollection<T> collection)
         {
             return new ObservableCollectionWatcher<T>(collection);
         }
 
-        /// <summary>Get a watcher for a net collection.</summary>
+        /// <summary>Get a watcher for a collection that never changes.</summary>
         /// <typeparam name="T">The value type.</typeparam>
-        /// <typeparam name="TSelf">The net field instance type.</typeparam>
-        /// <param name="field">The net collection.</param>
-        public static NetValueWatcher<T, TSelf> ForNetValue<T, TSelf>(NetFieldBase<T, TSelf> field) where TSelf : NetFieldBase<T, TSelf>
+        public static ICollectionWatcher<T> ForImmutableCollection<T>()
         {
-            return new NetValueWatcher<T, TSelf>(field);
+            return ImmutableCollectionWatcher<T>.Instance;
         }
 
         /// <summary>Get a watcher for a net collection.</summary>
         /// <typeparam name="T">The value type.</typeparam>
         /// <param name="collection">The net collection.</param>
-        public static NetCollectionWatcher<T> ForNetCollection<T>(NetCollection<T> collection) where T : class, INetObject<INetSerializable>
+        public static ICollectionWatcher<T> ForNetCollection<T>(NetCollection<T> collection) where T : class, INetObject<INetSerializable>
         {
             return new NetCollectionWatcher<T>(collection);
         }
diff --git a/src/SMAPI/Framework/StateTracking/LocationTracker.cs b/src/SMAPI/Framework/StateTracking/LocationTracker.cs
index 2249e41b..1f479e12 100644
--- a/src/SMAPI/Framework/StateTracking/LocationTracker.cs
+++ b/src/SMAPI/Framework/StateTracking/LocationTracker.cs
@@ -1,5 +1,4 @@
 using System.Collections.Generic;
-using System.Collections.ObjectModel;
 using System.Linq;
 using Microsoft.Xna.Framework;
 using StardewModdingAPI.Framework.StateTracking.FieldWatchers;
@@ -59,9 +58,7 @@ namespace StardewModdingAPI.Framework.StateTracking
             this.Location = location;
 
             // init watchers
-            this.BuildingsWatcher = location is BuildableGameLocation buildableLocation
-                ? WatcherFactory.ForNetCollection(buildableLocation.buildings)
-                : (ICollectionWatcher<Building>)WatcherFactory.ForObservableCollection(new ObservableCollection<Building>());
+            this.BuildingsWatcher = location is BuildableGameLocation buildableLocation ? WatcherFactory.ForNetCollection(buildableLocation.buildings) : WatcherFactory.ForImmutableCollection<Building>();
             this.DebrisWatcher = WatcherFactory.ForNetCollection(location.debris);
             this.LargeTerrainFeaturesWatcher = WatcherFactory.ForNetCollection(location.largeTerrainFeatures);
             this.NpcsWatcher = WatcherFactory.ForNetCollection(location.characters);