feat: add doubly-linked list implementation

src/tools/cache.spec.ts

@@ -0,0 +1,100 @@
+import { expect, test } from "@jest/globals";
+import { LRUCache, MRUCache } from "./cache";
+
+test("new LRU cache is not full", () => {
+    const cache = new LRUCache<number>(3);
+    expect(cache.isFull()).toBe(false);
+});
+
+test("put into empty LRU cache", () => {
+    const cache = new LRUCache<number>(3);
+    const value = cache.put(10);
+    expect(value).toBe(undefined);
+    expect(cache.oldest()).toBe(10);
+    expect(cache.oldest()).toBe(cache.newest());
+});
+
+test("remove from empty LRU cache", () => {
+    const cache = new LRUCache<number>(3);
+    cache.remove(10);
+    expect(cache.asArray()).toEqual({});
+});
+
+test("put into non-empty LRU cache", () => {
+    const cache = new LRUCache<number>(3);
+    cache.put(10);
+    cache.put(20);
+    const value = cache.put(30);
+    expect(value).toBe(undefined);
+    expect(cache.oldest()).toBe(10);
+    expect(cache.newest()).toBe(30);
+    expect(cache.asArray()).toEqual({ 1: 10, 2: 20, 3: 30 });
+});
+
+test("remove from non-empty LRU cache", () => {
+    const cache = new LRUCache<number>(3);
+    cache.put(10);
+    cache.put(20);
+    cache.remove(10);
+    expect(cache.oldest()).toBe(20);
+    expect(cache.asArray()).toEqual({ 1: 20 });
+});
+
+test("put into full LRU cache", () => {
+    const cache = new LRUCache<number>(3);
+    cache.put(10);
+    cache.put(20);
+    cache.put(30);
+    const value = cache.put(40);
+    expect(value).toBe(10);
+    expect(cache.asArray()).toEqual({ 1: 20, 2: 30, 3: 40 });
+});
+
+test("new MRU cache is not full", () => {
+    const cache = new MRUCache<number>(3);
+    expect(cache.isFull()).toBe(false);
+});
+
+test("remove from empty MRU uache", () => {
+    const cache = new MRUCache<number>(3);
+    cache.remove(10);
+    expect(cache.asArray()).toEqual({});
+});
+
+test("put into empty MRU cache", () => {
+    const cache = new MRUCache<number>(3);
+    const value = cache.put(10);
+    expect(value).toBe(undefined);
+    expect(cache.oldest()).toBe(10);
+    expect(cache.oldest()).toBe(cache.newest());
+});
+
+test("put into non-empty MRU cache", () => {
+    const cache = new MRUCache<number>(3);
+    cache.put(10);
+    cache.put(20);
+    const value = cache.put(30);
+    expect(value).toBe(undefined);
+    expect(cache.oldest()).toBe(10);
+    expect(cache.newest()).toBe(30);
+    expect(cache.asArray()).toEqual({ 1: 10, 2: 20, 3: 30 });
+});
+
+test("remove from non-empty MRU cache", () => {
+    const cache = new MRUCache<number>(3);
+    cache.put(10);
+    cache.put(20);
+    cache.remove(10);
+    expect(cache.oldest()).toBe(20);
+    expect(cache.asArray()).toEqual({ 1: 20 });
+});
+
+test("put into full MRU cache", () => {
+    const cache = new MRUCache<number>(3);
+    cache.put(10);
+    cache.put(20);
+    cache.put(30);
+    const value = cache.put(40);
+    expect(value).toBe(30);
+    expect(cache.asArray()).toEqual({ 1: 10, 2: 20, 3: 40 });
+});

src/tools/cache.ts

@@ -0,0 +1,67 @@
+import { LuaObj } from "@wowts/lua";
+import { List, ListNode } from "./list";
+
+class Cache<T> {
+    list: List<T>;
+    nodeByValue: LuaObj<ListNode<T>> = {};
+
+    constructor(public size: number) {
+        this.list = new List<T>();
+    }
+
+    isFull() {
+        return this.list.length >= this.size;
+    }
+
+    newest() {
+        return this.list.back();
+    }
+
+    oldest() {
+        return this.list.front();
+    }
+
+    asArray() {
+        return this.list.asArray();
+    }
+
+    evict() {
+        return this.list.shift();
+    }
+
+    put(value: T) {
+        this.remove(value);
+        const evicted = (this.isFull() && this.evict()) || undefined;
+        /* Pretend to cast to string to satisfy TypeScript.
+         * Lua tables can accept anything as a valid key.
+         */
+        const key = value as unknown as string;
+        this.nodeByValue[key] = this.list.push(value);
+        return evicted;
+    }
+
+    remove(value: T) {
+        /* Pretend to cast to string to satisfy TypeScript.
+         * Lua tables can accept anything as a valid key.
+         */
+        const key = value as unknown as string;
+        const node = this.nodeByValue[key];
+        if (node) {
+            this.list.remove(node);
+        }
+    }
+}
+
+export class LRUCache<T> extends Cache<T> {
+    evict() {
+        // LRU policy evicts the oldest item
+        return this.list.shift();
+    }
+}
+
+export class MRUCache<T> extends Cache<T> {
+    evict() {
+        // MRU policy evicts the newest item
+        return this.list.pop();
+    }
+}