code: def on_click(self, event):
          
          if event["button"] == 1:
              if self._running:
                  self._running = False
                  self._time_left = self._end_time - time()
                  if self._timer:
                      self._timer.cancel()
              else:
                  self._running = True
                  self._end_time = time() + self._time_left
                  if self._timer:
                      self._timer.cancel()
                  self._timer = Timer(self._time_left, self._time_up)
                  self._timer.start()
                  if self._active:
                      self.py3.play_sound(self.sound_pomodoro_start)
  
          elif event["button"] == 2:
              # reset
              self._init()
              if self._timer:
                  self._timer.cancel()
  
          elif event["button"] == 3:
              # advance
              self._advance(user_action=True)
              if self._timer:
                  self._timer.cancel()
docs: Handles click events:
              - left click starts an inactive counter and pauses a running
                Pomodoro
              - middle click resets everything
              - right click starts (and ends, if needed) a break