/// <summary>
/// Returns the first transition which occurs strictly after the given instant.
/// </summary>
/// <remarks>
/// If the given instant is before the starting year, the year of the given instant is
/// adjusted to the beginning of the starting year. The first transition after the
/// adjusted instant is determined. If the next adjustment is after the ending year, this
/// method returns null; otherwise the next transition is returned.
/// </remarks>
/// <param name="instant">The <see cref="Instant"/> lower bound for the next transition.</param>
/// <param name="standardOffset">The <see cref="Offset"/> standard offset.</param>
/// <param name="previousSavings">The <see cref="Offset"/> savings adjustment at the given Instant.</param>
/// <returns>The next transition, or null if there is no next transition. The transition may be
/// infinite, i.e. after the end of representable time.</returns>
internal Transition?Next(Instant instant, Offset standardOffset, Offset previousSavings)
{
Offset ruleOffset = YearOffset.GetRuleOffset(standardOffset, previousSavings);
Offset newOffset = standardOffset + Savings;
LocalInstant safeLocal = instant.SafePlus(ruleOffset);
int targetYear;
if (safeLocal < minLocalInstant)
{
// Asked for a transition after some point before the first transition: crop to first year (so we get the first transition)
targetYear = FromYear;
}
else if (safeLocal >= maxLocalInstant)
{
// Asked for a transition after our final transition... or both are beyond the end of time (in which case
// we can return an infinite transition). This branch will always be taken for transitions beyond the end
// of time.
return(maxLocalInstant == LocalInstant.AfterMaxValue ? new Transition(Instant.AfterMaxValue, newOffset) : (Transition?)null);
}
else if (safeLocal == LocalInstant.BeforeMinValue)
{
// We've been asked to find the next transition after some point which is a valid instant, but is before the
// start of valid local time after applying the rule offset. For example, passing Instant.MinValue for a rule which says
// "transition uses wall time, which is UTC-5". Proceed as if we'd been asked for something in -9998.
// I *think* that works...
targetYear = GregorianYearMonthDayCalculator.MinGregorianYear;
}
else
{
// Simple case: we were asked for a "normal" value in the range of years for which this recurrence is valid.
int ignoredDayOfYear;
targetYear = CalendarSystem.Iso.YearMonthDayCalculator.GetYear(safeLocal.DaysSinceEpoch, out ignoredDayOfYear);
}
LocalInstant transition = YearOffset.GetOccurrenceForYear(targetYear);
Instant safeTransition = transition.SafeMinus(ruleOffset);
if (safeTransition > instant)
{
return(new Transition(safeTransition, newOffset));
}
// We've got a transition earlier than we were asked for. Try next year.
// Note that this will stil be within the FromYear/ToYear range, otherwise
// safeLocal >= maxLocalInstant would have been triggered earlier.
targetYear++;
// Handle infinite transitions
if (targetYear > GregorianYearMonthDayCalculator.MaxGregorianYear)
{
return(new Transition(Instant.AfterMaxValue, newOffset));
}
// It's fine for this to be "end of time", and it can't be "start of time" because we're at least finding a transition in -9997.
safeTransition = YearOffset.GetOccurrenceForYear(targetYear).SafeMinus(ruleOffset);
return(new Transition(safeTransition, newOffset));
}
/// <summary>
/// Returns the last transition which occurs before or on the given instant.
/// </summary>
/// <param name="instant">The <see cref="Instant"/> lower bound for the next trasnition.</param>
/// <param name="standardOffset">The <see cref="Offset"/> standard offset.</param>
/// <param name="previousSavings">The <see cref="Offset"/> savings adjustment at the given Instant.</param>
/// <returns>The previous transition, or null if there is no previous transition. The transition may be
/// infinite, i.e. before the start of representable time.</returns>
internal Transition?PreviousOrSame(Instant instant, Offset standardOffset, Offset previousSavings)
{
Offset ruleOffset = YearOffset.GetRuleOffset(standardOffset, previousSavings);
Offset newOffset = standardOffset + Savings;
LocalInstant safeLocal = instant.SafePlus(ruleOffset);
int targetYear;
if (safeLocal > maxLocalInstant)
{
// Asked for a transition before some point after our last year: crop to last year.
targetYear = ToYear;
}
// Deliberately < here; "previous or same" means if safeLocal==minLocalInstant, we should compute it for this year.
else if (safeLocal < minLocalInstant)
{
// Asked for a transition before our first one
return(null);
}
else if (!safeLocal.IsValid)
{
if (safeLocal == LocalInstant.BeforeMinValue)
{
// We've been asked to find the next transition before some point which is a valid instant, but is before the
// start of valid local time after applying the rule offset. It's possible that the next transition *would*
// be representable as an instant (e.g. 1pm Dec 31st -9999 with an offset of -5) but it's reasonable to
// just return an infinite transition.
return(new Transition(Instant.BeforeMinValue, newOffset));
}
else
{
// We've been asked to find the next transition before some point which is a valid instant, but is after the
// end of valid local time after applying the rule offset. For example, passing Instant.MaxValue for a rule which says
// "transition uses wall time, which is UTC+5". Proceed as if we'd been asked for something in 9999.
// I *think* that works...
targetYear = GregorianYearMonthDayCalculator.MaxGregorianYear;
}
}
else
{
// Simple case: we were asked for a "normal" value in the range of years for which this recurrence is valid.
targetYear = CalendarSystem.Iso.YearMonthDayCalculator.GetYear(safeLocal.DaysSinceEpoch, out int ignoredDayOfYear);
}
LocalInstant transition = YearOffset.GetOccurrenceForYear(targetYear);
Instant safeTransition = transition.SafeMinus(ruleOffset);
if (safeTransition <= instant)
{
return(new Transition(safeTransition, newOffset));
}
// We've got a transition later than we were asked for. Try next year.
// Note that this will stil be within the FromYear/ToYear range, otherwise
// safeLocal < minLocalInstant would have been triggered earlier.
targetYear--;
// Handle infinite transitions
if (targetYear < GregorianYearMonthDayCalculator.MinGregorianYear)
{
return(new Transition(Instant.BeforeMinValue, newOffset));
}
// It's fine for this to be "start of time", and it can't be "end of time" because we're at latest finding a transition in 9998.
safeTransition = YearOffset.GetOccurrenceForYear(targetYear).SafeMinus(ruleOffset);
return(new Transition(safeTransition, newOffset));
}