public DateTime GetNextOccurrence(DateTime baseTime, DateTime endTime)
        {
            const int nil = -1;

            var baseYear   = baseTime.Year;
            var baseMonth  = baseTime.Month;
            var baseDay    = baseTime.Day;
            var baseHour   = baseTime.Hour;
            var baseMinute = baseTime.Minute;

            var endYear  = endTime.Year;
            var endMonth = endTime.Month;
            var endDay   = endTime.Day;

            var year   = baseYear;
            var month  = baseMonth;
            var day    = baseDay;
            var hour   = baseHour;
            var minute = baseMinute + 1;

            //
            // Minute
            //

            minute = _minutes.Next(minute);

            if (minute == nil)
            {
                minute = _minutes.GetFirst();
                hour++;
            }

            //
            // Hour
            //

            hour = _hours.Next(hour);

            if (hour == nil)
            {
                minute = _minutes.GetFirst();
                hour   = _hours.GetFirst();
                day++;
            }
            else if (hour > baseHour)
            {
                minute = _minutes.GetFirst();
            }

            //
            // Day
            //

            day = _days.Next(day);

RetryDayMonth:

            if (day == nil)
            {
                minute = _minutes.GetFirst();
                hour   = _hours.GetFirst();
                day    = _days.GetFirst();
                month++;
            }
            else if (day > baseDay)
            {
                minute = _minutes.GetFirst();
                hour   = _hours.GetFirst();
            }

            //
            // Month
            //

            month = _months.Next(month);

            if (month == nil)
            {
                minute = _minutes.GetFirst();
                hour   = _hours.GetFirst();
                day    = _days.GetFirst();
                month  = _months.GetFirst();
                year++;
            }
            else if (month > baseMonth)
            {
                minute = _minutes.GetFirst();
                hour   = _hours.GetFirst();
                day    = _days.GetFirst();
            }

            //
            // The day field in a cron expression spans the entire range of days
            // in a month, which is from 1 to 31. However, the number of days in
            // a month tend to be variable depending on the month (and the year
            // in case of February). So a check is needed here to see if the
            // date is a border case. If the day happens to be beyond 28
            // (meaning that we're dealing with the suspicious range of 29-31)
            // and the date part has changed then we need to determine whether
            // the day still makes sense for the given year and month. If the
            // day is beyond the last possible value, then the day/month part
            // for the schedule is re-evaluated. So an expression like "0 0
            // 15,31 * *" will yield the following sequence starting on midnight
            // of Jan 1, 2000:
            //
            //  Jan 15, Jan 31, Feb 15, Mar 15, Apr 15, Apr 31, ...
            //

            var dateChanged = day != baseDay || month != baseMonth || year != baseYear;

            if (day > 28 && dateChanged && day > Calendar.GetDaysInMonth(year, month))
            {
                if (year >= endYear && month >= endMonth && day >= endDay)
                {
                    return(endTime);
                }

                day = nil;
                goto RetryDayMonth;
            }

            var nextTime = new DateTime(year, month, day, hour, minute, 0, 0, baseTime.Kind);

            if (nextTime >= endTime)
            {
                return(endTime);
            }

            //
            // Day of week
            //

            if (_daysOfWeek.Contains((int)nextTime.DayOfWeek))
            {
                return(nextTime);
            }

            return(GetNextOccurrence(new DateTime(year, month, day, 23, 59, 0, 0, baseTime.Kind), endTime));
        }