function autoReply() {
  Logger.log('Script start');
  var strCalendarOOFKey = 'OOF';
  var strUserEmailToSetVacationOn = 'steve.midgley.mixrun@gmail.com';
  // find calendar event
  var today = new Date();
  var msTodayStart = today.getTime();
  var msTodayEnd = today.getTime()+60000; // adding 1 min, but in effect it means start and end on the same day
  var unavailableToday = false;

  Logger.log('Looking for Calendar trigger "'+strCalendarOOFKey+'" for today '+today.toDateString());

  var events = CalendarApp.getDefaultCalendar().getEventsForDay(today, { search: 'OOF' });
  for (var i = 0; i < events.length; i++) {
    if(events[i].isAllDayEvent() && events[i].isOwnedByMe()) {
      Logger.log("Setting vacation response to true due to event titled '"+events[i].getTitle()+"'")
      unavailableToday = true;
      break;
      
    }
    
  }
  
  Logger.log("Setting Vacation response to: "+unavailableToday.toString());
  
  var jsonVacationSettingsOn = {
    "enableAutoReply": true,
    "responseSubject": "I'm currently out of the office",
    "responseBodyPlainText": "If you need any help while I'm gone contact x@y.com",
    "responseBodyHtml": "If you need any help while I'm gone contact x@y.com",
    "restrictToContacts": true,
    "restrictToDomain": false,
    "startTime": msTodayStart,
    "endTime": msTodayEnd
  };

  var jsonVacationSettingsOff = {
    "enableAutoReply": false,
  };

  if(unavailableToday == true){
    Logger.log('Updating Vacation Responder to On');
    var vacationSettings = Gmail.Users.Settings.updateVacation(
      jsonVacationSettingsOn,
      strUserEmailToSetVacationOn
    );
  } else {
    Logger.log('Updating Vacation Responder to Off');
    var vacationSettings = Gmail.Users.Settings.updateVacation(
      jsonVacationSettingsOff,
      strUserEmailToSetVacationOn
    );

  };

  Logger.log('Finished updating vacation responder:'+today.toDateString());
  
}