Add in-memory TTL cache utility

src/utils/cache.ts

@@ -0,0 +1,44 @@
+/**
+ * Simple in-memory TTL cache.
+ */
+export class Cache<T> {
+  private store = new Map<string, { value: T; expiresAt: number }>();
+
+  constructor(private ttlMs: number) {}
+
+  get(key: string): T | undefined {
+    const entry = this.store.get(key);
+    if (!entry) return undefined;
+    if (Date.now() > entry.expiresAt) {
+      this.store.delete(key);
+      return undefined;
+    }
+    return entry.value;
+  }
+
+  set(key: string, value: T): void {
+    this.store.set(key, { value, expiresAt: Date.now() + this.ttlMs });
+  }
+
+  /**
+   * Get a value from cache, or compute and store it if missing/expired.
+   * If the compute function throws, the error propagates to the caller
+   * and nothing is cached.
+   */
+  async getOrSet(key: string, fn: () => Promise<T>): Promise<T> {
+    const cached = this.get(key);
+    if (cached !== undefined) return cached;
+
+    const value = await fn();
+    this.set(key, value);
+    return value;
+  }
+
+  get size(): number {
+    return this.store.size;
+  }
+
+  clear(): void {
+    this.store.clear();
+  }
+}