export default class EventEmitter {
  private $listeners: Record<string, Function[]> = {};

  /**
   * once event listener
   * @param event
   * @param listener
   */
  public once(event: string, listener: Function) {
    let fn = (...args: any[]) => {
      listener.apply(null, args);
      this.removeListener(event, fn);
    };
    this.addListener(event, fn);
    return this;
  }

  /**
   * add event listener
   * @param event
   * @param listener
   */
  public addListener(event: string, listener: Function) {
    this.$listeners[event] = this.$listeners[event] || [];
    if (this.$listeners[event].indexOf(listener) === -1) {
      this.$listeners[event].push(listener);
    }

    return this;
  }

  /**
   * emit event
   * @param event
   * @param args
   */
  public emit(event: string, ...args: any[]) {
    (this.$listeners[event] || []).forEach((fn) => {
      fn.apply(null, args);
    });
  }

  /**
   * remove one event listener
   * @param event
   * @param listener
   */
  public removeListener(event: string, listener: Function) {
    this.$listeners[event] = (this.$listeners[event] || []).filter((fn) => fn !== listener);
  }

  /**
   * remove all event
   * @param event
   */
  public removeAllListener(event?: string) {
    if (event) {
      this.$listeners[event] = [];
    } else {
      this.$listeners = {};
    }
  }
}