init commit

shared/utils/src/lru-map.ts

@@ -0,0 +1,60 @@
+/**
+ * LRU Map implementation storing key/values up to a provided size limit. Beyond that
+ * size limit, the least recently used entry is evicted.
+ *
+ * @see https://github.pie.apple.com/isao/lru-map
+ */
+export class LruMap<K, V> extends Map<K, V> {
+    private sizeLimit: number;
+
+    constructor(sizeLimit: number) {
+        super();
+        this.setSizeLimit(sizeLimit);
+        // Needed to convince TS that this is set (it's actually handled by setSizeLimit)
+        this.sizeLimit = sizeLimit;
+    }
+
+    /**
+     * Retrieve a value from the map with a given key.
+     * @param key The key for the entry
+     * @return value The entry's value (or undefined if non existent)
+     */
+    get(key: K): V | undefined {
+        let value: V | undefined;
+
+        if (this.has(key)) {
+            value = super.get(key);
+
+            // Map entries are always in insertion order. So
+            // readding, pushes this entry to the top of the LRU.
+            this.delete(key);
+            super.set(key, value!);
+        }
+
+        return value;
+    }
+
+    set(key: K, value: V): this {
+        super.set(key, value);
+        this.prune();
+        return this;
+    }
+
+    setSizeLimit(newSizeLimit: number): void {
+        if (newSizeLimit < 0 || !isFinite(newSizeLimit)) {
+            throw new Error(
+                `setSizeLimit expects finite positive number, got: ${newSizeLimit}`,
+            );
+        }
+
+        this.sizeLimit = newSizeLimit;
+        this.prune();
+    }
+
+    private prune(): void {
+        while (this.size > this.sizeLimit) {
+            const leastRecentlyUsedKey = this.keys().next().value;
+            this.delete(leastRecentlyUsedKey);
+        }
+    }
+}