export class Observable {
  private _eventListeners: any[] = [];
  private _object: any = null;

  constructor(object) {
    this._object = object;
  }

  on(eventName, callback) {
    if (this.indexOf(eventName, callback) !== -1) {
      console.warn(`The following callback is already added to the event: ${eventName}`, callback);
      return;
    }
    this._eventListeners.push({
      eventName,
      callback,
    });
  }

  off(eventName, callback) {
    const idx = this.indexOf(eventName, callback);
    if (idx !== -1) {
      this._eventListeners.splice(idx, 1);
    }
  }

  indexOf(eventName, callback) {
    for (let o = 0; o < this._eventListeners.length; o++) {
      const el = this._eventListeners[o];
      if (el.eventName === eventName && el.callback === callback) {
        return o;
      }
    }
    return -1;
  }

  triggerEvent(eventName, eventData) {
    setTimeout(() => {
      for (const el of this._eventListeners) {
        if (el.eventName === eventName) {
          el.callback(this._object, eventData);
        }
      }
    });
  }
}