code: def determine_alert(self, action_schedule, issue_creation_time, last_alert):
          
          issue_age = time.time() - issue_creation_time
          alert_schedule_lookup = {pytimeparse.parse(action_time): action_time for action_time in action_schedule}
          alert_schedule = sorted(alert_schedule_lookup.keys())
          last_alert_time = pytimeparse.parse(last_alert)
  
          for alert_time in alert_schedule:
              if last_alert_time < alert_time <= issue_age and last_alert_time != alert_time:
                  return alert_schedule_lookup[alert_time]
          else:
              return None
docs: Determine if we need to trigger an alert
  
          Args:
              action_schedule (`list`): A list contains the alert schedule
              issue_creation_time (`int`): Time we create the issue
              last_alert (`str`): Time we sent the last alert
  
          Returns:
              (`None` or `str`)
              None if no alert should be sent. Otherwise return the alert we should send