// a Map that forgets the least recently used entries past max_size
export class LruMap<K, V> {
	#map = new Map<K, V>();
	readonly max_size: number;

	constructor(max_size: number) {
		this.max_size = max_size;
	}

	get(key: K): V | undefined {
		const value = this.#map.get(key);
		if (value !== undefined) {
			// maps keep insertion order, so re-inserting moves it to the back
			this.#map.delete(key);
			this.#map.set(key, value);
		}
		return value;
	}

	set(key: K, value: V) {
		this.#map.delete(key);
		this.#map.set(key, value);
		if (this.#map.size > this.max_size) {
			this.#map.delete(this.#map.keys().next().value!);
		}
	}

	delete(key: K) {
		this.#map.delete(key);
	}

	get size() {
		return this.#map.size;
	}
}