internal static BclAdjustmentRule FromWindowsAdjustmentRule(TimeZoneInfo zone, TimeZoneInfo.AdjustmentRule rule)
{
// With .NET 4.6, adjustment rules can have their own standard offsets, allowing
// a much more reasonable set of time zone data. Unfortunately, this isn't directly
// exposed, but we can detect it by just finding the UTC offset for an arbitrary
// time within the rule - the start, in this case - and then take account of the
// possibility of that being in daylight saving time. Fortunately, we only need
// to do this during the setup.
var ruleStandardOffset = zone.GetUtcOffset(rule.DateStart);
if (zone.IsDaylightSavingTime(rule.DateStart))
{
ruleStandardOffset -= rule.DaylightDelta;
}
var standardOffset = ruleStandardOffset.ToOffset();
// Although the rule may have its own standard offset, the start/end is still determined
// using the zone's standard offset.
var zoneStandardOffset = zone.BaseUtcOffset.ToOffset();
// Note: this extends back from DateTime.MinValue to start of time, even though the BCL can represent
// as far back as 1AD. This is in the *spirit* of a rule which goes back that far.
var start = rule.DateStart == DateTime.MinValue ? Instant.BeforeMinValue : rule.DateStart.ToLocalDateTime().WithOffset(zoneStandardOffset).ToInstant();
// The end instant (exclusive) is the end of the given date, so we need to add a day.
var end = rule.DateEnd == MaxDate ? Instant.AfterMaxValue : rule.DateEnd.ToLocalDateTime().PlusDays(1).WithOffset(zoneStandardOffset).ToInstant();
var savings = rule.DaylightDelta.ToOffset();
PartialZoneIntervalMap partialMap;
// Some rules have DST start/end of "January 1st", to indicate that they're just in standard time. This is important
// for rules which have a standard offset which is different to the standard offset of the zone itself.
if (IsStandardOffsetOnlyRule(rule))
{
partialMap = PartialZoneIntervalMap.ForZoneInterval(zone.StandardName, start, end, standardOffset, Offset.Zero);
}
else
{
var daylightRecurrence = new ZoneRecurrence(zone.DaylightName, savings, ConvertTransition(rule.DaylightTransitionStart), int.MinValue, int.MaxValue);
var standardRecurrence = new ZoneRecurrence(zone.StandardName, Offset.Zero, ConvertTransition(rule.DaylightTransitionEnd), int.MinValue, int.MaxValue);
IZoneIntervalMap recurringMap = new StandardDaylightAlternatingMap(standardOffset, standardRecurrence, daylightRecurrence);
// Fake 1 hour savings if the adjustment rule claims to be 0 savings. See DaylightFakingZoneIntervalMap documentation below for more details.
if (savings == Offset.Zero)
{
recurringMap = new DaylightFakingZoneIntervalMap(recurringMap, zone.DaylightName);
}
partialMap = new PartialZoneIntervalMap(start, end, recurringMap);
}
return(new BclAdjustmentRule(start, end, standardOffset, savings, partialMap));
}
/// <summary>
/// Reads a time zone from the specified reader.
/// </summary>
/// <param name="reader">The reader.</param>
/// <param name="id">The id.</param>
/// <returns>The time zone.</returns>
internal static DateTimeZone Read([Trusted][NotNull] IDateTimeZoneReader reader, [Trusted][NotNull] string id)
{
Preconditions.DebugCheckNotNull(reader, nameof(reader));
Preconditions.DebugCheckNotNull(id, nameof(id));
int size = reader.ReadCount();
var periods = new ZoneInterval[size];
// It's not entirely clear why we don't just assume that the first zone interval always starts at Instant.BeforeMinValue
// (given that we check that later) but we don't... and changing that now could cause compatibility issues.
var start = reader.ReadZoneIntervalTransition(null);
for (int i = 0; i < size; i++)
{
var name = reader.ReadString();
var offset = reader.ReadOffset();
var savings = reader.ReadOffset();
var nextStart = reader.ReadZoneIntervalTransition(start);
periods[i] = new ZoneInterval(name, start, nextStart, offset, savings);
start = nextStart;
}
var tailZone = reader.ReadByte() == 1 ? StandardDaylightAlternatingMap.Read(reader) : null;
return(new PrecalculatedDateTimeZone(id, periods, tailZone));
}
