private void OnNextWave(object sender, NextWaveEventArgs args)
 {
     if(args.GameOver) {
         Debug.Log("Received game over message!");
     } else {
         WaveButton.interactable = true;
     }
 }
        //On wave completion stop listening for the wave complete event
        //and move to the next wave
        private void OnWaveComplete(object sender, EventArgs args)
        {
            Debug.Log("Wave complete!");
            _currentWave.WaveCompleteEvent -= OnWaveComplete;

            NextWaveEventArgs nextWaveArgs = new NextWaveEventArgs();
            if (_currentWaveIndex + 1 >= _waves.Count) {
                nextWaveArgs.GameOver = true;
            } else {
                nextWaveArgs.GameOver = false;
            }

            NextWaveEvent(this, nextWaveArgs);
        }