export class PubSub {
  #target = new EventTarget();

  publish(trigger: string, payload: unknown): Promise<void> {
    this.#target.dispatchEvent(new CustomEvent(trigger, { detail: payload }));
    return Promise.resolve();
  }

  asyncIterator<T>(triggers: string | string[]): AsyncIterableIterator<T> {
    const names = Array.isArray(triggers) ? triggers : [triggers];
    const pulls: Array<(result: IteratorResult<T>) => void> = [];
    const pushes: T[] = [];
    let done = false;

    const listener = (event: Event) => {
      const value = (event as CustomEvent<T>).detail;
      const pull = pulls.shift();

      if (pull)
        pull({ done: false, value });
      else
        pushes.push(value);
    };

    for (const name of names)
      this.#target.addEventListener(name, listener);

    const close = (): Promise<IteratorResult<T>> => {
      if (!done) {
        done = true;

        for (const name of names)
          this.#target.removeEventListener(name, listener);

        for (const pull of pulls.splice(0))
          pull({ done: true, value: undefined });

        pushes.length = 0;
      }

      return Promise.resolve({ done: true, value: undefined });
    };

    return {
      next: () => {
        if (done)
          return Promise.resolve({ done: true, value: undefined });

        if (pushes.length > 0)
          return Promise.resolve({ done: false, value: pushes.shift() as T });

        return new Promise((resolve) => pulls.push(resolve));
      },
      return: close,
      throw: (error: unknown) => {
        close();
        return Promise.reject(error);
      },
      [Symbol.asyncIterator]() {
        return this;
      }
    };
  }
}