Get offset from Utc on any system/time zone

Question

Hello experts,

Need to get the current system's time zone offset from UTC:

This:

TimeZone.CurrentTimeZone.GetUtcOffset(Now.Date).TotalHours.ToString

Will not show the correct value when in the daylight saving period.

This one seems to work correctly:

TimeZoneInfo.Local.BaseUtcOffset.ToString

So 2 questions, is TimeZoneInfo.Local.BaseUtcOffset.ToString always working as expected on all time zones and both in standard / daylight time?

Second, this returns "-05:00:00", is there a formatter to get it as "-05:00" ?

And show positive offset "14:00:00" as "+14:00".

Thanks in advance :)

Answer 1

Check out NodaTime NuGet package.

using NodaTime;

namespace TODO;
/// <summary>
///
/// Patterns for Offset values
/// https://nodatime.org/3.1.x/userguide/offset-patterns
///
/// Time zone list
/// https://nodatime.org/TimeZones
/// https://gist.github.com/jrolstad/5ca7d78dbfe182d7c1be
/// </summary>
internal static class TimeOperations
{
    private static string TimeZoneOffset(string timeZoneId, DateTime dateTimeUtc)
    {
        
        Instant instant = Instant.FromDateTimeUtc(dateTimeUtc);
        DateTimeZone zone = DateTimeZoneProviders.Tzdb[timeZoneId];

        ZonedDateTime dateTime = new ZonedDateTime(instant, zone);
        var daylightSavings = dateTime.IsDaylightSavingsTime();
        Offset offset = daylightSavings? zone.MinOffset : zone.MaxOffset;
        return offset.ToString("m", null);
    }

    private static bool IsDaylightSavingsTime(this ZonedDateTime zonedDateTime)
    {
        var instant = zonedDateTime.ToInstant();
        var zoneInterval = zonedDateTime.Zone.GetZoneInterval(instant);
        return zoneInterval.Savings != Offset.Zero;
    }

    public static DateTime GetSysDateTimeNow(string zone = "US/Pacific")
    {
        Instant now = SystemClock.Instance.GetCurrentInstant();
        return now.InZone(DateTimeZoneProviders.Tzdb[zone]).ToDateTimeUnspecified();
    }
    public static string Cancun()
    {
        const string timeZoneId = "America/Cancun";
        var offset = TimeZoneOffset(timeZoneId, DateTime.SpecifyKind(GetSysDateTimeNow(timeZoneId), DateTimeKind.Utc));
        return offset;
    }

    public static string Local()
    {
        const string timeZoneId = "US/Pacific";
        var offset = TimeZoneOffset(timeZoneId, DateTime.SpecifyKind(GetSysDateTimeNow(), DateTimeKind.Utc));
        return offset;
    }

    public static string USEastern()
    {
        const string timeZoneId = "US/Eastern";
        var offset = TimeZoneOffset(timeZoneId, DateTime.SpecifyKind(GetSysDateTimeNow(timeZoneId), DateTimeKind.Utc));
        return offset;
    }
}