// Licensed to the .NET Foundation under one or more agreements. // The .NET Foundation licenses this file to you under the MIT license. // See the LICENSE file in the project root for more information. /*============================================================ ** ** ** ** Purpose: ** This class is used to represent a TimeZone. It ** has methods for converting a DateTime to UTC from local time ** and to local time from UTC and methods for getting the ** standard name and daylight name of the time zone. ** ** The only TimeZone that we support in version 1 is the ** CurrentTimeZone as determined by the system timezone. ** ** ============================================================*/ using System; using System.Text; using System.Threading; using System.Collections; using System.Globalization; namespace System { [Obsolete("System.TimeZone has been deprecated. Please investigate the use of System.TimeZoneInfo instead.")] public abstract class TimeZone { private static volatile TimeZone? currentTimeZone = null; // Private object for locking instead of locking on a public type for SQL reliability work. private static object? s_InternalSyncObject; private static object InternalSyncObject { get { if (s_InternalSyncObject == null) { object o = new object(); Interlocked.CompareExchange(ref s_InternalSyncObject, o, null); } return s_InternalSyncObject; } } protected TimeZone() { } public static TimeZone CurrentTimeZone { get { //Grabbing the cached value is required at the top of this function so that //we don't incur a race condition with the ResetTimeZone method below. TimeZone? tz = currentTimeZone; if (tz == null) { lock (InternalSyncObject) { if (currentTimeZone == null) { currentTimeZone = new CurrentSystemTimeZone(); } tz = currentTimeZone; } } return (tz); } } //This method is called by CultureInfo.ClearCachedData in response to control panel //change events. It must be synchronized because otherwise there is a race condition //with the CurrentTimeZone property above. internal static void ResetTimeZone() { if (currentTimeZone != null) { lock (InternalSyncObject) { currentTimeZone = null; } } } public abstract string StandardName { get; } public abstract string DaylightName { get; } public abstract TimeSpan GetUtcOffset(DateTime time); // // Converts the specified datatime to the Universal time base on the current timezone // public virtual DateTime ToUniversalTime(DateTime time) { if (time.Kind == DateTimeKind.Utc) { return time; } long tickCount = time.Ticks - GetUtcOffset(time).Ticks; if (tickCount > DateTime.MaxTicks) { return new DateTime(DateTime.MaxTicks, DateTimeKind.Utc); } if (tickCount < DateTime.MinTicks) { return new DateTime(DateTime.MinTicks, DateTimeKind.Utc); } return new DateTime(tickCount, DateTimeKind.Utc); } // // Convert the specified datetime value from UTC to the local time based on the time zone. // public virtual DateTime ToLocalTime(DateTime time) { if (time.Kind == DateTimeKind.Local) { return time; } bool isAmbiguousLocalDst = false; long offset = ((CurrentSystemTimeZone)(TimeZone.CurrentTimeZone)).GetUtcOffsetFromUniversalTime(time, ref isAmbiguousLocalDst); return new DateTime(time.Ticks + offset, DateTimeKind.Local, isAmbiguousLocalDst); } // Return an array of DaylightTime which reflects the daylight saving periods in a particular year. // We currently only support having one DaylightSavingTime per year. // If daylight saving time is not used in this timezone, null will be returned. public abstract DaylightTime GetDaylightChanges(int year); public virtual bool IsDaylightSavingTime(DateTime time) { return (IsDaylightSavingTime(time, GetDaylightChanges(time.Year))); } // Check if the specified time is in a daylight saving time. Allows the user to // specify the array of Daylight Saving Times. public static bool IsDaylightSavingTime(DateTime time, DaylightTime daylightTimes) { return CalculateUtcOffset(time, daylightTimes) != TimeSpan.Zero; } // // NOTENOTE: Implementation detail // In the transition from standard time to daylight saving time, // if we convert local time to Universal time, we can have the // following (take PST as an example): // Local Universal UTC Offset // ----- --------- ---------- // 01:00AM 09:00 -8:00 // 02:00 (=> 03:00) 10:00 -8:00 [This time doesn't actually exist, but it can be created from DateTime] // 03:00 10:00 -7:00 // 04:00 11:00 -7:00 // 05:00 12:00 -7:00 // // So from 02:00 - 02:59:59, we should return the standard offset, instead of the daylight saving offset. // // In the transition from daylight saving time to standard time, // if we convert local time to Universal time, we can have the // following (take PST as an example): // Local Universal UTC Offset // ----- --------- ---------- // 01:00AM 08:00 -7:00 // 02:00 (=> 01:00) 09:00 -8:00 // 02:00 10:00 -8:00 // 03:00 11:00 -8:00 // 04:00 12:00 -8:00 // // So in this case, the 02:00 does exist after the first 2:00 rolls back to 01:00. We don't need to special case this. // But note that there are two 01:00 in the local time. // // And imagine if the daylight saving offset is negative (although this does not exist in real life) // In the transition from standard time to daylight saving time, // if we convert local time to Universal time, we can have the // following (take PST as an example, but the daylight saving offset is -01:00): // Local Universal UTC Offset // ----- --------- ---------- // 01:00AM 09:00 -8:00 // 02:00 (=> 01:00) 10:00 -9:00 // 02:00 11:00 -9:00 // 03:00 12:00 -9:00 // 04:00 13:00 -9:00 // 05:00 14:00 -9:00 // // So in this case, the 02:00 does exist after the first 2:00 rolls back to 01:00. We don't need to special case this. // // In the transition from daylight saving time to standard time, // if we convert local time to Universal time, we can have the // following (take PST as an example, daylight saving offset is -01:00): // // Local Universal UTC Offset // ----- --------- ---------- // 01:00AM 10:00 -9:00 // 02:00 (=> 03:00) 11:00 -9:00 // 03:00 11:00 -8:00 // 04:00 12:00 -8:00 // 05:00 13:00 -8:00 // 06:00 14:00 -8:00 // // So from 02:00 - 02:59:59, we should return the daylight saving offset, instead of the standard offset. // internal static TimeSpan CalculateUtcOffset(DateTime time, DaylightTime daylightTimes) { if (daylightTimes == null) { return TimeSpan.Zero; } DateTimeKind kind = time.Kind; if (kind == DateTimeKind.Utc) { return TimeSpan.Zero; } DateTime startTime; DateTime endTime; // startTime and endTime represent the period from either the start of DST to the end and includes the // potentially overlapped times startTime = daylightTimes.Start + daylightTimes.Delta; endTime = daylightTimes.End; // For normal time zones, the ambiguous hour is the last hour of daylight saving when you wind the // clock back. It is theoretically possible to have a positive delta, (which would really be daylight // reduction time), where you would have to wind the clock back in the begnning. DateTime ambiguousStart; DateTime ambiguousEnd; if (daylightTimes.Delta.Ticks > 0) { ambiguousStart = endTime - daylightTimes.Delta; ambiguousEnd = endTime; } else { ambiguousStart = startTime; ambiguousEnd = startTime - daylightTimes.Delta; } bool isDst = false; if (startTime > endTime) { // In southern hemisphere, the daylight saving time starts later in the year, and ends in the beginning of next year. // Note, the summer in the southern hemisphere begins late in the year. if (time >= startTime || time < endTime) { isDst = true; } } else if (time >= startTime && time < endTime) { // In northern hemisphere, the daylight saving time starts in the middle of the year. isDst = true; } // If this date was previously converted from a UTC date and we were able to detect that the local // DateTime would be ambiguous, this data is stored in the DateTime to resolve this ambiguity. if (isDst && time >= ambiguousStart && time < ambiguousEnd) { isDst = time.IsAmbiguousDaylightSavingTime(); } if (isDst) { return daylightTimes.Delta; } return TimeSpan.Zero; } } }