private void changeDateRange(DateRangeParameter newDateRange)
        {
            startOfSelection = null;

            highlightDateRange(newDateRange);

            selectedDateRangeSubject.OnNext(newDateRange);
        }
        private void calendarDayTapped(CalendarDayViewModel tappedDay)
        {
            if (startOfSelection == null)
            {
                var date = tappedDay.DateTimeOffset;

                var dateRange = DateRangeParameter.WithDates(date, date);
                startOfSelection = tappedDay;
                highlightDateRange(dateRange);
            }
            else
            {
                var startDate = startOfSelection.DateTimeOffset;
                var endDate   = tappedDay.DateTimeOffset;

                var dateRange = DateRangeParameter.WithDates(startDate, endDate);
                startOfSelection = null;
                changeDateRange(dateRange);
            }
        }