CalendarSyncService

script.gs

// run this script as a trigger for your events spreadsheet to sync all the events with google calendar
function myFunction() {
  SpreadsheetApp.getActiveSpreadsheet().getActiveSheet().getDataRange().sort(1)
  
  Logger.log("Fetching calendar data...");
  
  // TODO: replace calendarId with actual id
  var cal = CalendarApp.getCalendarById(calendarId);
  
  var titles = fetchCalendarTitles(cal);  
    
  Logger.log("Fetching sheet data...");
  var data = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet().getDataRange().getValues();
  
  for (row in data) {
    var title = data[row][0] + "'s birthday";
    if (titles.indexOf(title) == -1) {
      // insert the entry in calendar
      var event = cal.createAllDayEventSeries(title, formatDate(data[row][1]), CalendarApp.newRecurrence().addYearlyRule())
      Logger.log("Adding new event: " + event.getTitle() + " (id: " + event.getId() + ")");
    }
  }
  
  Logger.log("Synchronization complete!") 
}

function fetchCalendarTitles(cal) {
  thisYear = new Date().getYear() + 1900;
  startDate = new Date(thisYear+'-1-1');
  endDate = new Date(thisYear+'-12-31');
  
  var events = cal.getEvents(startDate, endDate);
  titles = []
  for (e in events) {
    titles.push(events[e].getTitle());
  }
  return titles;
}

// convert dd/mm to date object
function formatDate(dt) {
  d = dt.split("/")[0];
  m = dt.split("/")[1];
  y = new Date().getYear() + 1900;
  return new Date(y+"-"+m+"-"+d);
}