CODEWITHSUNDEEP
c#datetimenodatime
victor
victor

Reputation: 1552

Noda Time - Create a ZonedDateTime from DateTime and TimeZoneId

Let's say I have the following date, time, and time zone: 2016-10-15, 1:00:00, America/Toronto.

How do I create a ZonedDateTime that represents that exact date and time in the specified zone?

Basically what I need a ZonedDateTime object that represents the exact date and time in the exact time zone.

In case the time is skipped, I would like to add the tick of hour to the new time. Example:

If 00:00 is skipped to 1:00, and I attempt to get the time 00:30 in the zone, I want the result to be 1:30, not only 1:00, which is the first time of the interval.

If 00:00 is skipped to 1:45, and I attempt to get the time 00:20 in the zone, I want the result ot be 2:05.

If a time is ambiguous, i. e., occurs twice, I want the earlir mapping.

Upvotes: 2

Views: 2394

Answers (2)

Jon Skeet
Jon Skeet

Reputation: 1500215

What you've described is precisely the behaviour of LocalDateTime.InZoneLeniently in Noda Time 2.0. (Thanks to Matt Johnson's change :) However, as that's still in alpha, here's a solution for 1.3.2. Basically, you just want an appropriate ZoneLocalMappingResolver, which you can build using Resolvers. Here's a complete example.

using NodaTime.TimeZones;
using NodaTime.Text;

class Program
{
    static void Main(string[] args)
    {
        // Paris went forward from UTC+1 to UTC+2
        // at 2am local time on March 29th 2015, and back
        // from UTC+2 to UTC+1 at 3am local time on October 25th 2015.
        var zone = DateTimeZoneProviders.Tzdb["Europe/Paris"];

        ResolveLocal(new LocalDateTime(2015, 3, 29, 2, 30, 0), zone);
        ResolveLocal(new LocalDateTime(2015, 6, 19, 2, 30, 0), zone);
        ResolveLocal(new LocalDateTime(2015, 10, 25, 2, 30, 0), zone);
    }

    static void ResolveLocal(LocalDateTime input, DateTimeZone zone)
    {
        // This can be cached in a static field; it's thread-safe.
        var resolver = Resolvers.CreateMappingResolver(
            Resolvers.ReturnEarlier, ShiftForward);

        var result = input.InZone(zone, resolver);
        Console.WriteLine("{0} => {1}", input, result);
    }

    static ZonedDateTime ShiftForward(
        LocalDateTime local,
        DateTimeZone zone,
        ZoneInterval intervalBefore,
        ZoneInterval intervalAfter)
    {
        var instant = new OffsetDateTime(local, intervalBefore.WallOffset)
            .WithOffset(intervalAfter.WallOffset)
            .ToInstant();
        return new ZonedDateTime(instant, zone);
    }            
}

Output:

29/03/2015 02:30:00 => 2015-03-29T03:30:00 Europe/Paris (+02)
19/06/2015 02:30:00 => 2015-06-19T02:30:00 Europe/Paris (+02)
25/10/2015 02:30:00 => 2015-10-25T02:30:00 Europe/Paris (+02)

Upvotes: 6

victor
victor

Reputation: 1552

Edit
There were problems with the previous solution, suchs as invalid datetimes during DST, etc.

Here's the new solution that accounts for everything, with explanation. Thanks to @Veeram.

// Transform the "time" in a localized time.                
var tzLocalTime = LocalDateTime.FromDateTime(time);

try
{
    // To get the exact same time in the specified zone.
    zoned = tzLocalTime.InZoneStrictly(zone);
}
catch(SkippedTimeException)
{
    // This happens if the time is skipped
    // because of daylight saving time.
    //
    // Example:
    // If DST starts at Oct 16 00:00:00,
    // then the clock is advanced by 1 hour
    // which means Oct 16 00:00:00 is *skipped*
    // to Oct 16 01:00:00.
    // In this case, it is not possible to convert
    // to exact same date, and SkippedTImeException
    // is thrown.

    // InZoneLeniently will convert the time
    // to the start of the zone interval after
    // the skipped date.
    // For the example above, this would return Oct 16 01:00:00.

     // If someone schedules an appointment at a time that
     // will not occur, than it is ok to adjust it to what
     // will really happen in the real world.

     var originalTime = ste.LocalDateTime;

     // Correct for the minutes, seconds, and milliseconds.
     // This is needed because if someone schedueld an appointment
     // as 00:30:00 when 00:00:00 is skipped, we expect the minute information
     // to be as expected: 01:30:00, instead of 01:00:00.
     var minuteSecondMillisecond = Duration.FromMinutes(originalTime.Minute) + Duration.FromSeconds(originalTime.Second) + Duration.FromMilliseconds(originalTime.Millisecond);

     zoned = zLocalTime.InZoneLeniently(zone).Plus(minuteSecondMillisecond);
}
catch(AmbiguousTimeException ate)
{
    // This happens when the time is ambiguous.
    // During daylight saving time, for example,
    // an hour might happen twice.
    //
    // Example:
    // If DST ends on Feb 19 00:00:00, then
    // Feb 18 23:00:00 will happen twice:
    // once during DST, and once when DST ends
    // and the clock is set back.
    // In such case, we assume the earlier mapping.
    // We could work with the second time that time
    // occur with ate.LaterMapping.

    zoned = ate.EarlierMapping;
}

Upvotes: 1

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