internal override LocalInstant AddMonths(LocalInstant localInstant, int months)
{
// Note: this method gives the same result regardless of the month numbering used
// by the instance. The method works in terms of civil month numbers for most of
// the time in order to simplify the logic.
if (months == 0)
{
return(localInstant);
}
long tickOfDay = TimeOfDayCalculator.GetTickOfDay(localInstant);
var startDate = HebrewScripturalCalculator.HebrewFromAbsolute(AbsoluteDayFromLocalInstant(localInstant));
int year = startDate.Year;
int month = HebrewMonthConverter.ScripturalToCivil(year, startDate.Month);
// This arithmetic works the same both backwards and forwards.
year += (months / MonthsPerLeapCycle) * YearsPerLeapCycle;
months = months % MonthsPerLeapCycle;
if (months > 0)
{
// Add as many months as we need to in order to act as if we'd begun at the start
// of the year, for simplicity.
months += month - 1;
// Add a year at a time
while (months >= GetMaxMonth(year))
{
months -= GetMaxMonth(year);
year++;
}
// However many months we've got left to add tells us the final month.
month = months + 1;
}
else
{
// Pretend we were given the month at the end of the years.
months -= GetMaxMonth(year) - month;
// Subtract a year at a time
while (months + GetMaxMonth(year) <= 0)
{
months += GetMaxMonth(year);
year--;
}
// However many months we've got left to add (which will still be negative...)
// tells us the final month.
month = GetMaxMonth(year) + months;
}
// Convert back to scriptural for the last bit
month = HebrewMonthConverter.CivilToScriptural(year, month);
int day = Math.Min(HebrewScripturalCalculator.DaysInMonth(year, month), startDate.Day);
int absoluteDay = HebrewScripturalCalculator.AbsoluteFromHebrew(year, month, day);
return(LocalInstantFromAbsoluteDay(absoluteDay, tickOfDay));
}
/// <summary>
/// Change the year, maintaining month and day as well as possible. This doesn't
/// work in the same way as other calendars; see http://judaism.stackexchange.com/questions/39053
/// for the reasoning behind the rules.
/// </summary>
internal override LocalInstant SetYear(LocalInstant localInstant, int year)
{
long tickOfDay = TimeOfDayCalculator.GetTickOfDay(localInstant);
int absoluteSourceDay = AbsoluteDayFromLocalInstant(localInstant);
YearMonthDay ymd = HebrewScripturalCalculator.HebrewFromAbsolute(absoluteSourceDay);
int targetDay = ymd.Day;
int targetScripturalMonth = ymd.Month;
if (targetScripturalMonth == 13 && !IsLeapYear(year))
{
// If we were in Adar II and the target year is not a leap year, map to Adar.
targetScripturalMonth = 12;
}
else if (targetScripturalMonth == 12 && IsLeapYear(year) && !IsLeapYear(ymd.Year))
{
// If we were in Adar (non-leap year), go to Adar II rather than Adar I in a leap year.
targetScripturalMonth = 13;
}
// If we're aiming for the 30th day of Heshvan, Kislev or an Adar, it's possible that the change in year
// has meant the day becomes invalid. In that case, roll over to the 1st of the subsequent month.
if (targetDay == 30 && (targetScripturalMonth == 8 || targetScripturalMonth == 9 || targetScripturalMonth == 12))
{
if (HebrewScripturalCalculator.DaysInMonth(year, targetScripturalMonth) != 30)
{
targetDay = 1;
targetScripturalMonth++;
// From Adar, roll to Nisan.
if (targetScripturalMonth == 13)
{
targetScripturalMonth = 1;
}
}
}
int absoluteTargetDay = HebrewScripturalCalculator.AbsoluteFromHebrew(year, targetScripturalMonth, targetDay);
return(LocalInstantFromAbsoluteDay(absoluteTargetDay, tickOfDay));
}
/// <summary>
/// Change the year, maintaining month and day as well as possible. This doesn't
/// work in the same way as other calendars; see https://judaism.stackexchange.com/questions/39053
/// for the reasoning behind the rules.
/// </summary>
internal override YearMonthDay SetYear(YearMonthDay yearMonthDay, int year)
{
int currentYear = yearMonthDay.Year;
int currentMonth = yearMonthDay.Month;
int targetDay = yearMonthDay.Day;
int targetScripturalMonth = CalendarToScripturalMonth(currentYear, currentMonth);
if (targetScripturalMonth == 13 && !IsLeapYear(year))
{
// If we were in Adar II and the target year is not a leap year, map to Adar.
targetScripturalMonth = 12;
}
else if (targetScripturalMonth == 12 && IsLeapYear(year) && !IsLeapYear(currentYear))
{
// If we were in Adar (non-leap year), go to Adar II rather than Adar I in a leap year.
targetScripturalMonth = 13;
}
// If we're aiming for the 30th day of Heshvan, Kislev or an Adar, it's possible that the change in year
// has meant the day becomes invalid. In that case, roll over to the 1st of the subsequent month.
if (targetDay == 30 && (targetScripturalMonth == 8 || targetScripturalMonth == 9 || targetScripturalMonth == 12))
{
if (HebrewScripturalCalculator.DaysInMonth(year, targetScripturalMonth) != 30)
{
targetDay = 1;
targetScripturalMonth++;
// From Adar, roll to Nisan.
if (targetScripturalMonth == 13)
{
targetScripturalMonth = 1;
}
}
}
int targetCalendarMonth = ScripturalToCalendarMonth(year, targetScripturalMonth);
return(new YearMonthDay(year, targetCalendarMonth, targetDay));
}
internal override int GetDaysInMonth(int year, int month) => HebrewScripturalCalculator.DaysInMonth(year, CalendarToScripturalMonth(year, month));
internal override int GetDaysInMonth(int year, int month)
{
return(HebrewScripturalCalculator.DaysInMonth(year, calendarToScriptural(year, month)));
}