// https://spin.atomicobject.com/2018/09/10/javascript-concurrency/

export class Mutex {
  private mutex = Promise.resolve();

  public lock(): PromiseLike<() => void> {
    let begin: (unlock: () => void) => void = () => { };

    this.mutex = this.mutex.then(() => {
      return new Promise(begin);
    });

    return new Promise((res) => {
      begin = res;
    });
  }

  public async dispatch<T>(fn: (() => T) | (() => PromiseLike<T>)): Promise<T> {
    const unlock = await this.lock();
    try {
      return await Promise.resolve(fn());
    } finally {
      unlock();
    }
  }
}