How do I round a DateTime to the nearest Period

Question

I want to be able to round any given Instant to the nearest Period to support grouping of data.

i.e. someone might want to group by 2 week periods, so given an Instant, I want to be able to work out the nearest instant (before or after) on the period boundary where "now" is considered to be the end of the current period. If today is Tuesday, then consider that this 2 week Period ends this week. Given any date (from now backward) I'd like to calculate the "2 week Period" that it fits in to.

// pseudo code

Period sevenDays = Days.SEVEN;

Instant nearestWeek = sevenDays.roundToNearest(new DateTime());

Period twelveHours = Hours.hours(12);

Instant nearestHalfDay = twelveHours.roundToNearest(new DateTime());

I hope that makes sense, any help or pointers greatly appreciated.

Answer 1

Ok, this is one solution I made myself but I really think this functionality should be built into Joda Time.

public static DateTime dateTimeFloor(DateTime dt, Period p) {
    if (p.getYears() != 0) {
        return dt.yearOfEra().roundFloorCopy().minusYears(dt.getYearOfEra() % p.getYears());
    } else if (p.getMonths() != 0) {
        return dt.monthOfYear().roundFloorCopy().minusMonths((dt.getMonthOfYear() - 1) % p.getMonths());
    } else if (p.getWeeks() != 0) {
        return dt.weekOfWeekyear().roundFloorCopy().minusWeeks((dt.getWeekOfWeekyear() - 1) % p.getWeeks());
    } else if (p.getDays() != 0) {
        return dt.dayOfMonth().roundFloorCopy().minusDays((dt.getDayOfMonth() - 1) % p.getDays());
    } else if (p.getHours() != 0) {
        return dt.hourOfDay().roundFloorCopy().minusHours(dt.getHourOfDay() % p.getHours());
    } else if (p.getMinutes() != 0) {
        return dt.minuteOfHour().roundFloorCopy().minusMinutes(dt.getMinuteOfHour() % p.getMinutes());
    } else if (p.getSeconds() != 0) {
        return dt.secondOfMinute().roundFloorCopy().minusSeconds(dt.getSecondOfMinute() % p.getSeconds());
    }
    return dt.millisOfSecond().roundCeilingCopy().minusMillis(dt.getMillisOfSecond() % p.getMillis());
}