/// <summary>
/// Returns the days at the start of the given week-year. The week-year may be
/// 1 higher or lower than the max/min calendar year. For non-regular rules (i.e. where some weeks
/// can be short) it returns the day when the week-year *would* have started if it were regular.
/// So this *always* returns a date on firstDayOfWeek.
/// </summary>
private int GetWeekYearDaysSinceEpoch(YearMonthDayCalculator yearMonthDayCalculator, [Trusted] int weekYear)
{
unchecked
{
// Need to be slightly careful here, as the week-year can reasonably be (just) outside the calendar year range.
// However, YearMonthDayCalculator.GetStartOfYearInDays already handles min/max -/+ 1.
int startOfCalendarYear = yearMonthDayCalculator.GetStartOfYearInDays(weekYear);
int startOfYearDayOfWeek = unchecked (startOfCalendarYear >= -3 ? 1 + ((startOfCalendarYear + 3) % 7)
: 7 + ((startOfCalendarYear + 4) % 7));
// How many days have there been from the start of the week containing
// the first day of the year, until the first day of the year? To put it another
// way, how many days in the week *containing* the start of the calendar year were
// in the previous calendar year.
// (For example, if the start of the calendar year is Friday and the first day of the week is Monday,
// this will be 4.)
int daysIntoWeek = ((startOfYearDayOfWeek - (int)firstDayOfWeek) + 7) % 7;
int startOfWeekContainingStartOfCalendarYear = startOfCalendarYear - daysIntoWeek;
bool startOfYearIsInWeek1 = (7 - daysIntoWeek >= minDaysInFirstWeek);
return(startOfYearIsInWeek1
? startOfWeekContainingStartOfCalendarYear
: startOfWeekContainingStartOfCalendarYear + 7);
}
}
/// <inheritdoc />
public int GetWeeksInWeekYear(int weekYear, CalendarSystem calendar)
{
Preconditions.CheckNotNull(calendar, nameof(calendar));
YearMonthDayCalculator yearMonthDayCalculator = calendar.YearMonthDayCalculator;
ValidateWeekYear(weekYear, calendar);
unchecked
{
int startOfWeekYear = GetWeekYearDaysSinceEpoch(yearMonthDayCalculator, weekYear);
int startOfCalendarYear = yearMonthDayCalculator.GetStartOfYearInDays(weekYear);
// The number of days gained or lost in the week year compared with the calendar year.
// So if the week year starts on December 31st of the previous calendar year, this will be +1.
// If the week year starts on January 2nd of this calendar year, this will be -1.
int extraDaysAtStart = startOfCalendarYear - startOfWeekYear;
// At the end of the year, we may have some extra days too.
// In a non-regular rule, we just round up, so assume we effectively have 6 extra days.
// In a regular rule, there can be at most minDaysInFirstWeek - 1 days "borrowed"
// from the following year - because if there were any more, those days would be in the
// the following year instead.
int extraDaysAtEnd = irregularWeeks ? 6 : minDaysInFirstWeek - 1;
int daysInThisYear = yearMonthDayCalculator.GetDaysInYear(weekYear);
// We can have up to "minDaysInFirstWeek - 1" days of the next year, too.
return((daysInThisYear + extraDaysAtStart + extraDaysAtEnd) / 7);
}
}
/// <inheritdoc />
public int GetWeeksInWeekYear(int weekYear, [NotNull] CalendarSystem calendar)
{
Preconditions.CheckNotNull(calendar, nameof(calendar));
YearMonthDayCalculator yearMonthDayCalculator = calendar.YearMonthDayCalculator;
ValidateWeekYear(weekYear, calendar);
unchecked
{
int startOfWeekYear = GetWeekYearDaysSinceEpoch(yearMonthDayCalculator, weekYear);
int startOfCalendarYear = yearMonthDayCalculator.GetStartOfYearInDays(weekYear);
// The number of days gained or lost in the week year compared with the calendar year.
// So if the week year starts on December 31st of the previous calendar year, this will be +1.
// If the week year starts on January 2nd of this calendar year, this will be -1.
int extraDaysAtStart = startOfCalendarYear - startOfWeekYear;
// At the end of the year, we may have some extra days too.
// In a non-regular rule, we just round up, so assume we effectively have 6 extra days.
// TODO: Explain the reasoning for the regular rule part. I know it works, I just
// don't know why.
int extraDaysAtEnd = irregularWeeks ? 6: minDaysInFirstWeek - 1;
int daysInThisYear = yearMonthDayCalculator.GetDaysInYear(weekYear);
// We can have up to "minDaysInFirstWeek - 1" days of the next year, too.
return((daysInThisYear + extraDaysAtStart + extraDaysAtEnd) / 7);
}
}
private int GetWeeksInWeekYear([Trusted] int weekYear)
{
unchecked
{
int startOfWeekYear = GetWeekYearDaysSinceEpoch(weekYear);
int startOfCalendarYear = yearMonthDayCalculator.GetStartOfYearInDays(weekYear);
// The number of days gained or lost in the week year compared with the calendar year.
// So if the week year starts on December 31st of the previous calendar year, this will be +1.
// If the week year starts on January 2nd of this calendar year, this will be -1.
int extraDays = startOfCalendarYear - startOfWeekYear;
int daysInThisYear = yearMonthDayCalculator.GetDaysInYear(weekYear);
// We can have up to "minDaysInFirstWeek - 1" days of the next year, too.
return((daysInThisYear + extraDays + (minDaysInFirstWeek - 1)) / 7);
}
}
/// <inheritdoc />
public int GetWeeksInWeekYear(int weekYear, [NotNull] CalendarSystem calendar)
{
Preconditions.CheckNotNull(calendar, nameof(calendar));
YearMonthDayCalculator yearMonthDayCalculator = calendar.YearMonthDayCalculator;
ValidateWeekYear(weekYear, calendar);
unchecked
{
int startOfWeekYear = GetWeekYearDaysSinceEpoch(yearMonthDayCalculator, weekYear);
int startOfCalendarYear = yearMonthDayCalculator.GetStartOfYearInDays(weekYear);
// The number of days gained or lost in the week year compared with the calendar year.
// So if the week year starts on December 31st of the previous calendar year, this will be +1.
// If the week year starts on January 2nd of this calendar year, this will be -1.
int extraDays = startOfCalendarYear - startOfWeekYear;
int daysInThisYear = yearMonthDayCalculator.GetDaysInYear(weekYear);
// We can have up to "minDaysInFirstWeek - 1" days of the next year, too.
return((daysInThisYear + extraDays + (minDaysInFirstWeek - 1)) / 7);
}
}
/// <summary>
/// Returns the days at the start of the given week-year. The week-year may be
/// 1 higher or lower than the max/min calendar year.
/// </summary>
private int GetWeekYearDaysSinceEpoch(YearMonthDayCalculator yearMonthDayCalculator, [Trusted] int weekYear)
{
unchecked
{
// Need to be slightly careful here, as the week-year can reasonably be (just) outside the calendar year range.
// However, YearMonthDayCalculator.GetStartOfYearInDays already handles min/max -/+ 1.
int startOfCalendarYear = yearMonthDayCalculator.GetStartOfYearInDays(weekYear);
int startOfYearDayOfWeek = unchecked (startOfCalendarYear >= -3 ? 1 + ((startOfCalendarYear + 3) % 7)
: 7 + ((startOfCalendarYear + 4) % 7));
if (startOfYearDayOfWeek > (8 - minDaysInFirstWeek))
{
// First week is end of previous year because it doesn't have enough days.
return(startOfCalendarYear + (8 - startOfYearDayOfWeek));
}
else
{
// First week is start of this year because it has enough days.
return(startOfCalendarYear - (startOfYearDayOfWeek - 1));
}
}
}