rewrite world/player state tracking (#453)

1 files changed, 62 insertions, 0 deletions

diff --git a/src/SMAPI/Framework/StateTracking/FieldWatchers/ComparableWatcher.cs b/src/SMAPI/Framework/StateTracking/FieldWatchers/ComparableWatcher.cs
new file mode 100644
index 00000000..d51fc2ac
--- /dev/null
+++ b/src/SMAPI/Framework/StateTracking/FieldWatchers/ComparableWatcher.cs
@@ -0,0 +1,62 @@
+using System;
+using System.Collections.Generic;
+
+namespace StardewModdingAPI.Framework.StateTracking.FieldWatchers
+{
+    /// <summary>A watcher which detects changes to a value using a specified <see cref="IEqualityComparer{T}"/> instance.</summary>
+    internal class ComparableWatcher<T> : IValueWatcher<T>
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>Get the current value.</summary>
+        private readonly Func<T> GetValue;
+
+        /// <summary>The equality comparer.</summary>
+        private readonly IEqualityComparer<T> Comparer;
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>The field value at the last reset.</summary>
+        public T PreviousValue { get; private set; }
+
+        /// <summary>The latest value.</summary>
+        public T CurrentValue { get; private set; }
+
+        /// <summary>Whether the value changed since the last reset.</summary>
+        public bool IsChanged { get; private set; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="getValue">Get the current value.</param>
+        /// <param name="comparer">The equality comparer which indicates whether two values are the same.</param>
+        public ComparableWatcher(Func<T> getValue, IEqualityComparer<T> comparer)
+        {
+            this.GetValue = getValue;
+            this.Comparer = comparer;
+            this.PreviousValue = getValue();
+        }
+
+        /// <summary>Update the current value if needed.</summary>
+        public void Update()
+        {
+            this.CurrentValue = this.GetValue();
+            this.IsChanged = !this.Comparer.Equals(this.PreviousValue, this.CurrentValue);
+        }
+
+        /// <summary>Set the current value as the baseline.</summary>
+        public void Reset()
+        {
+            this.PreviousValue = this.CurrentValue;
+            this.IsChanged = false;
+        }
+
+        /// <summary>Release any references if needed when the field is no longer needed.</summary>
+        public void Dispose() { }
+    }
+}