nopaque.UsersExtension = class UsersExtension {
  #data;
  #promises;

  constructor(app) {
    this.app = app;

    this.#data = {};
    this.app.data.users = this.#data;

    this.#promises = {
      get: {},
      subscribe: {}
    };
  }

  async #get(userId) {
    const response = await this.app.socket.emitWithAck('users.get', userId);

    if (response.status != 200) {
      throw new Error(`[${response.status}] ${response.statusText}`);
    }

    this.#data[userId] = response.body;
    return this.#data[userId];
  }

  get(userId) {
    if (userId in this.#promises.get) {
      return this.#promises.get[userId];
    }

    this.#promises.get[userId] = this.#get(userId);
    return this.#promises.get[userId];
  }

  async #subscribe(userId) {
    const response = await this.app.socket.emitWithAck('users.subscribe', userId);

    if (response.status != 200) {
      throw new Error(`[${response.status}] ${response.statusText}`);
    }
  }

  subscribe(userId) {
    if (userId in this.#promises.subscribe) {
      return this.#promises.subscribe[userId];
    }

    this.#promises.subscribe[userId] = this.#subscribe(userId);
    return this.#promises.subscribe[userId];
  }
}