function addDays(date, dayAdd) {
	millisec = (dayAdd) * 86400000;
	newTime = date.getTime() + millisec;
	return new Date(newTime);
}
function diffDays(date1, date2) {
	diff = Math.floor((date2.getTime() - date1.getTime())/86400000  );
	return diff;
}

function setLastDay() {

  var date_ini_str = document.getElementById('arr_date').value;
  var date_end_str = document.getElementById('dep_date').value;
  var date_ini_ = date_ini_str.split("-");
  var date_end_ = date_end_str.split("-");
	var dataStart = new Date(date_ini_[0],date_ini_[1]-1,date_ini_[2],12);
	var dataEnd = new Date(date_end_[0],date_end_[1]-1,date_end_[2],12);

	if (dataStart>=dataEnd) {
      dataEnd = addDays (dataStart, Number(document.getElementById('nights').value));
      var d  = dataEnd.getDate();
      var day = (d < 10) ? '0' + d : d;
      var m = dataEnd.getMonth() + 1;
      var month = (m < 10) ? '0' + m : m;
      document.getElementById('dep_date').value = dataEnd.getFullYear()+"-"+month+"-"+day;
  } else {
      setNumNights();
  }

	return true;
}

function setNumNights() {
  var date_ini_str = document.getElementById('arr_date').value;
  var date_end_str = document.getElementById('dep_date').value;
  var date_ini_=date_ini_str.split("-");
  var date_end_=date_end_str.split("-");
	var dataStart = new Date(date_ini_[0],date_ini_[1]-1,date_ini_[2],12);
	var dataEnd = new Date(date_end_[0],date_end_[1]-1,date_end_[2],12);
	
	if (dataStart<dataEnd) {
		document.getElementById('nights').value=diffDays(dataStart, dataEnd);
	} else {
			document.getElementById('nights').value=2;
			setLastDay();
	}
	return true;
}