TaskPool.ts

type Task<T> = () => Promise<T>;

export class TaskPool {
  #isReady: boolean;
  #current: Task<unknown> | null;
  readonly #queue: Task<unknown>[];

  constructor(
    params: {
      readonly isReady?: boolean;
    } = {},
  ) {
    this.#isReady = params.isReady ?? false;
    this.#current = null;
    this.#queue = [];
  }

  notifyReady(): void {
    this.#isReady = true;
    this.#check();
  }

  #check(): void {
    if (this.#current == null && this.#isReady) {
      this.#current = this.#queue.shift() ?? null;
      void this.#current?.().finally(() => {
        this.#current = null;
        this.#check();
      });
    }
  }

  waitFor<T>(task: Task<T>): Promise<T> {
    return new Promise((resolve, reject) => {
      this.#queue.push(() => task().then(resolve).catch(reject));
      this.#check();
    });
  }
}