encapsulate & cache asset operation groups (#766)

This is needed for the upcoming Stardew Valley 1.6 to avoid duplicate checks between DoesAssetExist and Load calls, and to make sure the answer doesn't change between them.

1 files changed, 51 insertions, 0 deletions

diff --git a/src/SMAPI/Framework/Utilities/TickCacheDictionary.cs b/src/SMAPI/Framework/Utilities/TickCacheDictionary.cs
new file mode 100644
index 00000000..1613a480
--- /dev/null
+++ b/src/SMAPI/Framework/Utilities/TickCacheDictionary.cs
@@ -0,0 +1,51 @@
+using System;
+using System.Collections.Generic;
+using StardewValley;
+
+namespace StardewModdingAPI.Framework.Utilities
+{
+    /// <summary>An in-memory dictionary cache that stores data for the duration of a game update tick.</summary>
+    /// <typeparam name="TKey">The dictionary key type.</typeparam>
+    /// <typeparam name="TValue">The dictionary value type.</typeparam>
+    internal class TickCacheDictionary<TKey, TValue>
+    {
+        /*********
+        ** Fields
+        *********/
+        /// <summary>The last game tick for which data was cached.</summary>
+        private int LastGameTick = -1;
+
+        /// <summary>The underlying cached data.</summary>
+        private readonly Dictionary<TKey, TValue> Cache = new();
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Get a value from the cache, fetching it first if it's not cached yet.</summary>
+        /// <param name="cacheKey">The unique key for the cached value.</param>
+        /// <param name="get">Get the latest data if it's not in the cache yet.</param>
+        public TValue GetOrSet(TKey cacheKey, Func<TValue> get)
+        {
+            // clear cache on new tick
+            if (Game1.ticks != this.LastGameTick)
+            {
+                this.Cache.Clear();
+                this.LastGameTick = Game1.ticks;
+            }
+
+            // fetch value
+            if (!this.Cache.TryGetValue(cacheKey, out TValue cached))
+                this.Cache[cacheKey] = cached = get();
+            return cached;
+        }
+
+        /// <summary>Remove an entry from the cache.</summary>
+        /// <param name="cacheKey">The unique key for the cached value.</param>
+        /// <returns>Returns whether the key was present in the dictionary.</returns>
+        public bool Remove(TKey cacheKey)
+        {
+            return this.Cache.Remove(cacheKey);
+        }
+    }
+}