Result cache LRU (#165)

* Give the result cache some LRU love

* Fixing LRU cache move-to-start, and simplifying

src/components/App/result-cache.ts

@@ -21,12 +21,13 @@ const SIZE = 5;
 
 export default class ResultCache {
   private readonly _entries: CacheEntry[] = [];
-  private _nextIndex: number = 0;
 
   add(entry: CacheEntry) {
     if (entry.encoderState.type === identity.type) throw Error('Cannot cache identity encodes');
-    this._entries[this._nextIndex] = entry;
-    this._nextIndex = (this._nextIndex + 1) % SIZE;
+    // Add the new entry to the start
+    this._entries.unshift(entry);
+    // Remove the last entry if we're now bigger than SIZE
+    if (this._entries.length > SIZE) this._entries.pop();
   }
 
   match(
@@ -34,7 +35,7 @@ export default class ResultCache {
     preprocessorState: PreprocessorState,
     encoderState: EncoderState,
   ): CacheResult | undefined {
-    const matchingEntry = this._entries.find((entry) => {
+    const matchingIndex = this._entries.findIndex((entry) => {
       // Check for quick exits:
       if (entry.source !== source) return false;
       if (entry.encoderState.type !== encoderState.type) return false;
@@ -55,14 +56,20 @@ export default class ResultCache {
       return true;
     });
 
-    if (matchingEntry) {
-      return {
-        bmp: matchingEntry.bmp,
-        preprocessed: matchingEntry.preprocessed,
-        file: matchingEntry.file,
-      };
+    if (matchingIndex === -1) return undefined;
+
+    const matchingEntry = this._entries[matchingIndex];
+
+    if (matchingIndex !== 0) {
+      // Move the matched result to 1st position (LRU)
+      this._entries.splice(matchingIndex, 1);
+      this._entries.unshift(matchingEntry);
     }
 
-    return undefined;
+    return {
+      bmp: matchingEntry.bmp,
+      preprocessed: matchingEntry.preprocessed,
+      file: matchingEntry.file,
+    };
   }
 }