export type EventHandler = (...args: any[]) => void;

export class SimpleEventEmitter {
  private _handlers: { [x: string]: EventHandler[] } = {};

  on(event: string, fn: EventHandler) {
    if (typeof fn !== 'function') {
      return;
    }

    if (!this._handlers[event]) {
      this._handlers[event] = [];
    }

    this._handlers[event].push(fn);
  }

  emit(event: string, ...args: any[]): void {
    if (!this._handlers[event]) {
      return;
    }

    this._handlers[event]
      .filter((fn) => fn && typeof fn === 'function')
      .forEach((fn) => fn(...args));
  }

  removeEventListener(event: string, fn: EventHandler): void {
    if (!this._handlers[event] || typeof fn !== 'function') {
      return;
    }

    const indexOf = this._handlers[event].indexOf(fn);
    if (indexOf > -1) {
      this._handlers[event].splice(indexOf, 1);
    }
  }
}