var d1 = flatpickr('#d1', {});
var d2 = flatpickr('#d2', {});

jQuery(document).ready(() => {
  jQuery('#calc').click(() => {
 var d1 = $('#d1').val();
  var d2 = $('#d2').val();
  jQuery('#dif').text(workingDaysBetweenDates(d1,d2));
  });
});

let workingDaysBetweenDates = (d0, d1) => {
  /* Two working days and an sunday (not working day) */
  var holidays = d'2016-05-03', '2016-05-05', '2016-05-07'];
  var startDate = parseDate(d0);
  var endDate = parseDate(d1);

console.log(startDate);
console.log(endDate);
Qualtrics.SurveyEngine.setEmbeddedData ( "startDate", startDate );
Qualtrics.SurveyEngine.setEmbeddedData ( "endDate", endDate );

// Validate input
  if (endDate < startDate) {
  return 0;
  }

// Calculate days between dates
  var millisecondsPerDay = 86400 * 1000; // Day in milliseconds
  startDate.setHours(0, 0, 0, 1); // Start just after midnight
  endDate.setHours(23, 59, 59, 999); // End just before midnight
  var diff = endDate - startDate; // Milliseconds between datetime objects
  var days = Math.ceil(diff / millisecondsPerDay);


  // Subtract two weekend days for every week in between
  var weeks = Math.floor(days / 7);
  days -= weeks * 2;

  // Handle special cases
  var startDay = startDate.getDay();
  var endDay = endDate.getDay();
 
  // Remove weekend not previously removed.
  if (startDay - endDay > 1) {
  days -= 2;
  }
  // Remove start day if span starts on Sunday but ends before Saturday
  if (startDay == 0 && endDay != 6) {
  days--;
  }
  // Remove end day if span ends on Saturday but starts after Sunday
  if (endDay == 6 && startDay != 0) {
  days--;
  }
  /* Here is the code */
  holidays.forEach(day => {
  if ((day >= d0) && (day <= d1)) {
  /* If it is not saturday (6) or sunday (0), substract it */
  if ((parseDate(day).getDay() % 6) != 0) {
  days--;

  }
} Qualtrics.SurveyEngine.setEmbeddedData ( "DaysBetween", days);
  });
  return days ;
}

function parseDate(input) {
  // Transform date from text to date
  var parts = input.match(/(\\d+)/g);
  // new Date(year, month m, date \, hours;, minutes , secondsy, ms]]]]])
  return new Date(parts[0], parts[1]-1, partsb2]); // months are 0-based
}