/// <summary>
/// Returns the difference TAI - UTC as of the given date, in seconds.
/// </summary>
/// <param name="date">The date.</param>
/// <returns>The difference.</returns>
public double GetTaiMinusUtc(JulianDate date)
{
LeapSecond toFind = new LeapSecond(date, 0.0);
// Start by assuming we're working with UTC, we'll check later if we're
// off by one because we really have TAI.
int index = m_leapSeconds.BinarySearch(toFind, s_compareLeapSecondDate);
if (index < 0)
{
index = ~index;
--index;
}
// Check if we're off by one because we're really working with TAI.
// If the requested date minus the most recent previous leap second offset is less than the date
// for the current leap second, then we haven't quite gotten to that leap second yet.
// This gets a little tricky because JulianDate and its conversion mechanisms try to outsmart us.
if (date.Standard == TimeStandard.InternationalAtomicTime)
{
JulianDate lastDate = GetDateForIndex(index);
JulianDate taiCutoff = new JulianDate(lastDate.Day, lastDate.SecondsOfDay, TimeStandard.InternationalAtomicTime);
taiCutoff += Duration.FromSeconds(GetOffsetForIndex(index));
if (date < taiCutoff)
{
--index;
}
}
return(GetOffsetForIndex(index));
}
/// <summary>
/// Try to convert <paramref name="date"/> from TAI to UTC, if possible.
/// </summary>
/// <param name="date">The date, which must be in the TAI
/// <see cref="TimeStandard"/>.</param>
/// <param name="result">Out parameter for returning the resulting UTC
/// <see cref="JulianDate"/>, if it was possible to convert.</param>
/// <returns><see langword="true"/> if <paramref name="date"/> could be converted
/// to UTC, otherwise false.</returns>
internal bool TryConvertTaiToUtc(JulianDate date, out JulianDate result)
{
//treat the request date as if it were UTC, and search for the most recent leap second.
LeapSecond toFind = new LeapSecond(date, 0.0);
int index = m_leapSeconds.BinarySearch(toFind, s_compareLeapSecondDate);
if (index < 0)
{
index = ~index;
--index;
}
//now we have the index of the most recent leap second that is after the requested date
if (index >= 0)
{
double mostRecentOffset = GetOffsetForIndex(index);
JulianDate leapSecondDate = GetDateForIndex(index);
if (date.Day == leapSecondDate.Day)
{
//if the requested date is on the day of the leap second, we may have to adjust
double secondsSinceLeapSecond = date.SecondsOfDay - leapSecondDate.SecondsOfDay;
if (secondsSinceLeapSecond >= mostRecentOffset - 1 &&
secondsSinceLeapSecond < mostRecentOffset)
{
//if the requested date is during the moment of a leap second, then we cannot convert to UTC.
result = JulianDate.MinValue;
return(false);
}
if (secondsSinceLeapSecond < mostRecentOffset)
{
//The leap second we found is actually after the desired date, as a result of simply treating the
//TAI date as if it were UTC. So, use the next previous leap second instead.
--index;
}
}
}
result = new JulianDate(date.Day, date.SecondsOfDay - GetOffsetForIndex(index), TimeStandard.CoordinatedUniversalTime);
return(true);
}
/// <summary>
/// Determines if a given day contains a leap second.
/// </summary>
/// <param name="julianDayNumber">The day, specified as a Julian day number.</param>
/// <returns>true if the day contains a leap second, otherwise false.</returns>
public bool DoesDayHaveLeapSecond(int julianDayNumber)
{
LeapSecond potentialLeapSecond = new LeapSecond(new JulianDate(julianDayNumber, 43200, TimeStandard.CoordinatedUniversalTime), 0.0);
return(m_leapSeconds.BinarySearch(potentialLeapSecond, s_compareLeapSecondDate) >= 0);
}
