/// <summary>
/// Work out the year, based on fields of:
/// - Year
/// - YearOfEra
/// - YearTwoDigits (implies YearOfEra)
/// - Era
///
/// If the year is specified, that trumps everything else - any other fields
/// are just used for checking.
///
/// If nothing is specified, the year of the template value is used.
///
/// If just the era is specified, the year of the template value is used,
/// and the specified era is checked against it. (Hopefully no-one will
/// expect to get useful information from a format string with era but no year...)
///
/// Otherwise, we have the year of era (possibly only two digits) and possibly the
/// era. If the era isn't specified, take it from the template value.
/// Finally, if we only have two digits, then use either the century of the template
/// value or the previous century if the year-of-era is greater than TwoDigitYearMax...
/// and if the template value isn't in the first century already.
///
/// Phew.
/// </summary>
private ParseResult <LocalDate> DetermineYear(PatternFields usedFields, string text)
{
if (usedFields.HasAny(PatternFields.Year))
{
if (Year > Calendar.MaxYear || Year < Calendar.MinYear)
{
return(ParseResult <LocalDate> .FieldValueOutOfRangePostParse(text, Year, 'u'));
}
if (usedFields.HasAny(PatternFields.Era) && Era != Calendar.GetEra(Year))
{
return(ParseResult <LocalDate> .InconsistentValues(text, 'g', 'u'));
}
if (usedFields.HasAny(PatternFields.YearOfEra))
{
int yearOfEraFromYear = Calendar.GetYearOfEra(Year);
if (usedFields.HasAny(PatternFields.YearTwoDigits))
{
// We're only checking the last two digits
yearOfEraFromYear = yearOfEraFromYear % 100;
}
if (yearOfEraFromYear != YearOfEra)
{
return(ParseResult <LocalDate> .InconsistentValues(text, 'y', 'u'));
}
}
return(null);
}
// Use the year from the template value, possibly checking the era.
if (!usedFields.HasAny(PatternFields.YearOfEra))
{
Year = TemplateValue.Year;
return(usedFields.HasAny(PatternFields.Era) && Era != Calendar.GetEra(Year)
? ParseResult <LocalDate> .InconsistentValues(text, 'g', 'u') : null);
}
if (!usedFields.HasAny(PatternFields.Era))
{
Era = TemplateValue.Era;
}
if (usedFields.HasAny(PatternFields.YearTwoDigits))
{
int century = TemplateValue.YearOfEra / 100;
if (YearOfEra > TwoDigitYearMax && century > 1)
{
century--;
}
YearOfEra += century * 100;
}
if (YearOfEra < Calendar.GetMinYearOfEra(Era) ||
YearOfEra > Calendar.GetMaxYearOfEra(Era))
{
return(ParseResult <LocalDate> .YearOfEraOutOfRange(text, YearOfEra, Era, Calendar));
}
Year = Calendar.GetAbsoluteYear(YearOfEra, Era);
return(null);
}