How to use timeZone of calendar to set timeZone for date object

Question

I want to use the calendar timezone to set the time zone of a date object. I'm looking for the proper technique. We have several bases around the nation, and each has their own calendar for journal and daily activities. We have multiple scripts that post to the calendars. I want to use the timezone of the calendar to set the date Object timezone, because the users travel around to different bases, and their computers might not be set to the correct time zone. We want to avoid incorrect time settings.

1. Should the script's timeZone be set to UTC?

2. This is where I'm currently at:

   function submitUiTest(e) {
     var app = UiApp.getActiveApplication();
     var cal = CalendarApp.getCalendarById('calendarId');
     var timeZone = cal.getTimeZone();
   
     var ss = SpreadsheetApp.getActiveSpreadsheet();
     var sheet = ss.getSheetByName('Sheet1');
   
     var startTime = e.parameter.startDate
     startTime.setHours(e.parameter.startHour, e.parameter.startMin, 0)
     startTime = formatTime(startTime, timeZone);
     Logger.log(startTime)
   
     var endTime = e.parameter.endDate
     endTime.setHours(e.parameter.endHour, e.parameter.endMin, 0);
     endTime = formatTime(endTime, timeZone);
     Logger.log(endTime)
   
     cal.createEvent('TimeZone Test', new Date(startTime), new Date(endTime));
   
     ss.appendRow([startTime, endTime]);
   
     return app;
   }
   
   function formatTime(time, timeZone){
     return Utilities.formatDate(time, (timeZone-time.getTimezoneOffset()), 'M/d/yyyy HH:mm');
   }
   

Edit: Currently there are 3 calendars, they are not user calendars, just each a separate calendar created for individual Air Stations. The air stations are each in separate time zone's. As crew members work at these stations they post daily activities to the calendars, and there are also several Ui scripts we have that post to the same calendars ex. a flight log. When an entry to a calendar is posted to any calendar, the time relates only to the timezone set on the script, not the timezone on the calendar. When the date or timestamp object is created, how can I use the timeZone that the calendar itself is set to.

What is best practice for scripts that record dates for different time zones? Set the script timezone to UTC and do the conversion? What do you use to get the user's timezone or in this case, I don't care what the user's timezone is set too, I need to use the timezone of the calendar.

Answer 1

Here is a modified version of the answer, without the UI stuff:

function gasTimezoneOffset(date, hour){
  var cal,calTimeZone,calTz,date,dateString,scriptTimeZone,sessionTz;

  var testMonth = "March",
      testDayOfMnth = "26",
      testYr = "2016",
      hour = "10:00",
      timeZoneDiff = 0;

  Logger.log("Script Time Zone: " + Session.getScriptTimeZone());

  dateString = testMonth + " " + testDayOfMnth + ", " + testYr;
  Logger.log("dateString: " + dateString);

  date = new Date(dateString);

  cal = CalendarApp.getDefaultCalendar();
  calTimeZone = cal.getTimeZone();

  calTimeZone = Utilities.formatDate(date, calTimeZone, 'Z');
  scriptTimeZone = Utilities.formatDate(date, Session.getTimeZone(), 'Z');

  calTz = Number(calTimeZone.slice(0,3));
  sessionTz = Number(scriptTimeZone.slice(0,3));

  //If both time zones are the same sign, get the difference between the
  //two.  E.g. -4 and -2.  Difference is 2
  //if each time zone is a different sign, add the absolute values together.
  //-4 and +1 should be 5
  if (calTz < 0 && sessionTz > 0 || calTz > 0 && sessionTz < 0){
    timeZoneDiff = Math.abs(Math.abs(calTz) + Math.abs(sessionTz));
  } else {
    timeZoneDiff = Math.abs(Math.abs(calTz) - Math.abs(sessionTz));
  };

  hour = Number(hour.slice(0,2));    
  return hour + timeZoneDiff;
};

Answer 2

EDIT : I wrote a small test UI and ran it with 2 calendars in 2 different timezones. Calendar events are created in the Calendar timezone and the user interface shows user values. Google takes care of timezone settings in both calendars and I didn't notice any anomalies : events where created as I wanted to, ie at the time shown in the UI in the calendar Timezone.

(screen capture)

Here is the code I used for testing :

var tz = [['test_agenda(pacific Time)','test_agenda'],['testencodage(Belgium time)','testencodage']]

function doGet() {
  var app = UiApp.createApplication().setStyleAttribute('padding','15PX');
  var hpanel = app.createHorizontalPanel();
  var dateBox = app.createDateBox().setId('dateBox').setName('dateBox');
  var hour = app.createListBox(false).setId('hour').setName('hour')
  for(h=0;h<25;++h){
    if(h/2==parseInt(h/2)){hour.addItem(parseInt(h/2)+':00')
                         }else{
                          hour.addItem(parseInt(h/2)+':30')
                         }
  }
  var amPm = app.createListBox(false).setId('am').setName('amPm')
  .addItem('AM').addItem('PM');
  var dateTimeLabel = app.createLabel('',false).setId('dateTimeLabel');
  var submit = app.createButton('Submit').setId('submit');
  var tzList = app.createListBox().setName('tzList');
    for(var c in tz){tzList.addItem(tz[c][0],tz[c][1])}
  var handler1 = app.createClientHandler().validateMatches(dateBox, '2','g').forEventSource().setEnabled(false);
  var handler2 = app.createServerHandler('createE').validateMatches(dateBox, '2','g').addCallbackElement(hpanel).addCallbackElement(tzList);
  submit.addClickHandler(handler1).addClickHandler(handler2);
  hpanel.add(dateBox).add(hour).add(amPm)
  app.add(hpanel);
  app.add(tzList).add(submit);
  app.add(dateTimeLabel);
  return app;
}

function createE(e) {
  var app = UiApp.getActiveApplication();
  var date = e.parameter.dateBox;
  var cal = CalendarApp.getCalendarsByName(e.parameter.tzList)[0]
  var timeZone = cal.getTimeZone();
  var sessionTz = Session.getTimeZone()
  Logger.log(sessionTz)
  Logger.log(timeZone)
  var hour = Number(e.parameter.hour.split(':')[0]);  
  var min = Number(e.parameter.hour.split(':')[1]);
  var amPm = e.parameter.amPm;
  if (amPm == 'PM' ){hour = hour+12};  // ADD 12 HOURS TO PM HOURS, EXCEPT 12PM
  if (hour == 24){hour = 0;amPm='AM'};  // HANDLE 12AM HOUR CORRECTLY
  var newDate=new Date(date)
  newDate.setHours(hour,min,0,0)
  Logger.log('start : '+newDate)
  var newDateString = Utilities.formatDate(newDate, sessionTz, 'MM/dd/yyyy hh:mm aaa');
  app.getElementById('dateTimeLabel').setText('tz = '+timeZone+' - '+newDateString);
  Logger.log('end : '+new Date(newDate.getTime()+3600000))
  cal.createEvent('test Event in TZ '+timeZone, newDate, new Date(newDate.getTime()+3600000))

  app.getElementById('submit').setEnabled(true);
  return app;
}

first comment :

I began to write a comment to ask you some questions but it was getting too long... so please consider this as a comment, not an answer ;-). I'm not sure I understand what you say about 'their computer not being set to the right timezone' the timezone of their computer is not relevant if they use Google Calendar, it is only a matter of parameter in Google Cal. If I understood your goal is that if the script sets an appointment at 8:00 AM they will see it shown at 8:00 AM in their Calendar wherever they are (8:00 AM in their 'local' timezone), right ?
So to summarize, you are running this script from one place and creating events for people in other timezones in their own calendars ? And are the users moving across different timezones ? These are 2 separate questions and it doesn't have one single solution. If a single user is moving across timezones all the events will be shifted unless he doesn't change his GCal parameters. But if he does so he won't be notified at the right time and the Calendar interface will be out of time... so that's not a reasonable solution. My last question : when you create an event in another calendar (in another tz) can it be an appointment between you and this person ? in other words is the absolute time of any importance for you use case ?

Answer 3

Ok here is a solution to the problem. I've probably went way out of my way or missed something simple but this finally works like I was hoping. Feel free to critique. I set the webapp timezone to GMT-0000 just for simplicity.

function uiTest() {
  var app = UiApp.createApplication();

  var startDate = app.createDateBox().setName('startDate').setId('startDate').setWidth('75');
  var startHour = app.createListBox().setName('startHour').setId('startHour').setWidth('45');
  var startMin = app.createListBox().setName('startMin').setId('startMin').setWidth('45');

  var endDate = app.createDateBox().setName('endDate').setId('endDate').setWidth('75');
  var endHour = app.createListBox().setName('endHour').setId('endHour').setWidth('45');
  var endMin = app.createListBox().setName('endMin').setId('endMin').setWidth('45');

  for (h=0;h<24;++h){
  if(h<10){
    var hourstr='0'+h
  }else{
    var hourstr=h.toString()
    }
  startHour.addItem(hourstr)
  endHour.addItem(hourstr)
  }
  for (m=0;m<60;++m){
  if(m<10){
    var minstr='0'+m
  }else{
    var minstr=m.toString()
    }
  startMin.addItem(minstr)
  endMin.addItem(minstr)
  }


  var grid = app.createFlexTable().setId('grid');
  app.add(grid);

  grid.setWidget(0, 0, app.createLabel('Start Date'));
  grid.setWidget(1, 0, startDate);

  grid.setWidget(0, 1, app.createLabel('Hour'));
  grid.setWidget(1, 1, startHour);


  grid.setWidget(0, 2, app.createLabel('Min'));
  grid.setWidget(1, 2, startMin);

  grid.setWidget(2, 0, app.createLabel('End Date'));
  grid.setWidget(3, 0, endDate);

  grid.setWidget(2, 1, app.createLabel('Hour'));
  grid.setWidget(3, 1, endHour);

  grid.setWidget(2, 2, app.createLabel('Min'));
  grid.setWidget(3, 2, endMin);



  app.add(app.createButton('Submit', app.createServerHandler('submitUiTest').addCallbackElement(grid)));

  SpreadsheetApp.getActiveSpreadsheet().show(app);  
}


function submitUiTest(e) {
  var app = UiApp.getActiveApplication();
  var cal = CalendarApp.getCalendarById('');//Info Sys Calendar set to Central Time
  //var cal = CalendarApp.getCalendarById('');//Fort Bliss (Mountain Time)
  var calTimeZone = cal.getTimeZone();

  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getSheetByName('Sheet1');


  var startTime = e.parameter.startDate
  startTime.setHours(gasTimezoneOffset(startTime, e.parameter.startHour, calTimeZone), e.parameter.startMin, 0);
  Logger.log('startTime: '+Utilities.formatDate(startTime, calTimeZone, 'M/d/yyyy HH:mm z'));

  var endTime = e.parameter.endDate
  endTime.setHours(gasTimezoneOffset(endTime, e.parameter.endHour, calTimeZone), e.parameter.endMin, 0);
  Logger.log('endTime: '+endTime)

  var timeStamp = Utilities.formatDate(startTime, calTimeZone, 'M/d/yyyy HH:mm z');

  cal.createEvent(timeStamp, new Date(startTime), new Date(endTime));

  ss.appendRow([startTime, endTime]);

  return app;
}


function gasTimezoneOffset(date, hour, calTimeZone){
  var calTz = new Number(Utilities.formatDate(date, calTimeZone, 'Z').substr(1,2));
  var sessionTz = new Number(Utilities.formatDate(date, Session.getTimeZone(), 'Z').substr(1,2));

  switch (Utilities.formatDate(date, calTimeZone, 'Z').substring(0,1)){
    case '+':
      var timeZoneOffset = sessionTz - calTz;
      break;
    case '-':
      var timeZoneOffset = sessionTz + calTz;
      break;
  }

  hour = new Number(hour);

  return hour + timeZoneOffset;
}

Answer 4

Here's the version of Sandy's code that I ended up using to create a function that takes the Calendar object and the "script time" and returns the "calendar time":

/**
 * Given a script date object, return the time in the user's calendar
 *
 * Sandy Good's answer to this SO question:
 *
 *   http://stackoverflow.com/questions/15645343/how-to-use-timezone-of-calendar-to-set-timezone-for-date-object
 *
 * @param {Date} scriptDateTime
 * @param {Calendar} calendar
 *
 * @return {Date} calendarDateTime
 */

function getCalendarDateTime (scriptDateTime, calendar) {

  Logger.log('scriptDateTime: ' + scriptDateTime)

  var calendarTimeZoneString = calendar.getTimeZone() 
  var calendarTimeZone = Utilities.formatDate(scriptDateTime, calendarTimeZoneString, 'Z')
  var calendarTz = Number(calendarTimeZone.slice(0,3)) 
  Logger.log('calendarTimeZone: %s (%s)', calendarTimeZoneString, calendarTz)

  var scriptTimeZoneString = Session.getScriptTimeZone()
  var scriptTimeZone = Utilities.formatDate(scriptDateTime, scriptTimeZoneString, 'Z')
  var sessionTz = Number(scriptTimeZone.slice(0,3))
  Logger.log('scriptTimeZone: %s (%s)', scriptTimeZoneString, sessionTz)

  // If both time zones are the same sign, get the difference between the
  // two.  E.g. -4 and -2.  Difference is 2
  // 
  // If each time zone is a different sign, add the absolute values together.
  // -4 and +1 should be 5

  var timeZoneDiff

  if (calendarTz < 0 && sessionTz > 0 || calendarTz > 0 && sessionTz < 0) {

    timeZoneDiff = Math.abs(Math.abs(calendarTz) + Math.abs(sessionTz))

  } else {

    timeZoneDiff = Math.abs(Math.abs(calendarTz) - Math.abs(sessionTz)) 
  }

  Logger.log('timeZoneDiff: ' + timeZoneDiff)

  var scriptHour = scriptDateTime.getHours()
  var calendarHour = scriptHour + timeZoneDiff

  var calendarDateTime = new Date(
    scriptDateTime.getYear(), 
    scriptDateTime.getMonth(),
    scriptDateTime.getDate(),
    calendarHour,
    scriptDateTime.getMinutes())

  Logger.log('calendarDateTime: ' + calendarDateTime)

  return calendarDateTime  
}

// Script is PST (GMT-8) and calendar is GMT

function test_getCalendarDateTime() {
  var calendar = CalendarApp.getDefaultCalendar()
  var scriptDateTime = new Date(2017, 0, 30, 12, 0) // 2017-01-30 12:00 PST
  var calendarDateTime = getCalendarDateTime(scriptDateTime, calendar) // 2017-01-30 20:00 PST
}

Answer 5

Could try deploying a separate web app for each time zone. Set the time zone of each app to match that of the unique calendar they are linked to. Since you only have 3 calendars in different time zones, seems like it would work for your case.