mcs/class/corlib/System/TimeZone.cs

   1 //
   2 // System.TimeZone.cs
   3 //
   4 // Authors:
   5 //   Duncan Mak (duncan@ximian.com)
   6 //   Ajay Kumar Dwivedi (adwiv@yahoo.com)
   7 //   Martin Baulig (martin@gnome.org)
   8 //
   9 // (C) Ximian, Inc.
  10 // Copyright (C) 2004-2006 Novell, Inc (http://www.novell.com)
  11 // Copyright 2011 Xamarin Inc.
  12 //
  13 // Permission is hereby granted, free of charge, to any person obtaining
  14 // a copy of this software and associated documentation files (the
  15 // "Software"), to deal in the Software without restriction, including
  16 // without limitation the rights to use, copy, modify, merge, publish,
  17 // distribute, sublicense, and/or sell copies of the Software, and to
  18 // permit persons to whom the Software is furnished to do so, subject to
  19 // the following conditions:
  20 //
  21 // The above copyright notice and this permission notice shall be
  22 // included in all copies or substantial portions of the Software.
  23 //
  24 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  25 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  26 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  27 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  28 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  29 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  30 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  31 //
  32 //
  33 // TODO:
  34 //
  35 //    Rewrite ToLocalTime to use GetLocalTimeDiff(DateTime,TimeSpan),
  36 //    this should only leave the validation at the beginning (for MaxValue)
  37 //    and then call the helper function.  This would remove all the
  38 //    ifdefs in that code, and replace it with only one, for the construction
  39 //    of the object.
  40 //
  41 //    Rewrite ToUniversalTime to use a similar setup to that
  42 //
  43 using System.Collections.Generic;
  44 using System.Globalization;
  45 using System.Runtime.CompilerServices;
  46 using System.Runtime.Serialization;
  47 using System.Runtime.InteropServices;
  48
  49 namespace System
  50 {
  51         [Serializable]
  52         [ComVisible (true)]
  53         public abstract class TimeZone
  54         {
  55                 // Fields
  56                 static TimeZone currentTimeZone;
  57
  58                 [NonSerialized]
  59                 static object tz_lock = new object ();
  60                 [NonSerialized]
  61                 static long timezone_check;
  62
  63                 // Constructor
  64                 protected TimeZone ()
  65                 {
  66                 }
  67
  68                 // Properties
  69                 public static TimeZone CurrentTimeZone {
  70                         get {
  71                                 long now = DateTime.UtcNow.Ticks;
  72                                 TimeZone tz = currentTimeZone;
  73
  74                                 lock (tz_lock) {
  75                                         if (tz == null || Math.Abs (now - timezone_check) > TimeSpan.TicksPerMinute) {
  76                                                 tz = new CurrentSystemTimeZone ();
  77                                                 timezone_check = now;
  78
  79                                                 currentTimeZone = tz;
  80                                         }
  81                                 }
  82
  83                                 return tz;
  84                         }
  85                 }
  86
  87                 public abstract string DaylightName {
  88                         get;
  89                 }
  90
  91                 public abstract string StandardName {
  92                         get;
  93                 }
  94
  95                 // Methods
  96                 public abstract DaylightTime GetDaylightChanges (int year);
  97
  98                 public abstract TimeSpan GetUtcOffset (DateTime time);
  99
 100                 public virtual bool IsDaylightSavingTime (DateTime time)
 101                 {
 102                         return IsDaylightSavingTime (time, GetDaylightChanges (time.Year));
 103                 }
 104
 105                 public static bool IsDaylightSavingTime (DateTime time, DaylightTime daylightTimes)
 106                 {
 107                         if (daylightTimes == null)
 108                                 throw new ArgumentNullException ("daylightTimes");
 109
 110                         // If Start == End, then DST is off
 111                         if (daylightTimes.Start.Ticks == daylightTimes.End.Ticks)
 112                                 return false;
 113
 114                         //We are in the northern hemisphere.
 115                         if (daylightTimes.Start.Ticks < daylightTimes.End.Ticks) {
 116                                 if (daylightTimes.Start.Ticks < time.Ticks && daylightTimes.End.Ticks > time.Ticks)
 117                                         return true; // time lies between Start and End
 118
 119                         }
 120                         else {  // We are in the southern hemisphere.
 121                                 if (time.Year == daylightTimes.Start.Year && time.Year == daylightTimes.End.Year)
 122                                         if (time.Ticks < daylightTimes.End.Ticks || time.Ticks > daylightTimes.Start.Ticks)
 123                                                 return true; // time is less than End OR more than Start
 124                         }
 125
 126                         return false;
 127                 }
 128
 129                 public virtual DateTime ToLocalTime (DateTime time)
 130                 {
 131                         if (time.Kind == DateTimeKind.Local)
 132                                 return time;
 133
 134                         TimeSpan utcOffset = GetUtcOffset (new DateTime (time.Ticks));
 135                         if (utcOffset.Ticks > 0) {
 136                                 if (DateTime.MaxValue - utcOffset < time)
 137                                         return DateTime.SpecifyKind (DateTime.MaxValue, DateTimeKind.Local);
 138                         } else if (utcOffset.Ticks < 0) {
 139                                 if (time.Ticks + utcOffset.Ticks < DateTime.MinValue.Ticks)
 140                                         return DateTime.SpecifyKind (DateTime.MinValue, DateTimeKind.Local);
 141                         }
 142
 143                         return DateTime.SpecifyKind (time.Add (utcOffset), DateTimeKind.Local);
 144                 }
 145
 146                 public virtual DateTime ToUniversalTime (DateTime time)
 147                 {
 148                         if (time.Kind == DateTimeKind.Utc)
 149                                 return time;
 150
 151                         TimeSpan offset = GetUtcOffset (time);
 152
 153                         if (offset.Ticks < 0) {
 154                                 if (DateTime.MaxValue + offset < time)
 155                                         return DateTime.SpecifyKind (DateTime.MaxValue, DateTimeKind.Utc);
 156                         } else if (offset.Ticks > 0) {
 157                                 if (DateTime.MinValue + offset > time)
 158                                         return DateTime.SpecifyKind (DateTime.MinValue, DateTimeKind.Utc);
 159                         }
 160
 161                         return DateTime.SpecifyKind (new DateTime (time.Ticks - offset.Ticks), DateTimeKind.Utc);
 162                 }
 163
 164                 internal static void ClearCachedData ()
 165                 {
 166                         currentTimeZone = null;
 167                 }
 168         }
 169
 170         [Serializable]
 171         internal class CurrentSystemTimeZone : TimeZone {
 172
 173                 readonly  TimeZoneInfo  LocalTimeZone;
 174
 175                 // Constructor
 176                 internal CurrentSystemTimeZone ()
 177                 {
 178                         LocalTimeZone = TimeZoneInfo.Local;
 179                 }
 180
 181                 public override string DaylightName {
 182                         get {
 183                                 return LocalTimeZone.DaylightName;
 184                         }
 185                 }
 186
 187                 public override string StandardName {
 188                         get {
 189                                 return LocalTimeZone.StandardName;
 190                         }
 191                 }
 192
 193                 public override System.Globalization.DaylightTime GetDaylightChanges (int year)
 194                 {
 195                         return LocalTimeZone.GetDaylightChanges (year);
 196                 }
 197
 198                 public override TimeSpan GetUtcOffset (DateTime dateTime)
 199                 {
 200                         if (dateTime.Kind == DateTimeKind.Utc)
 201                                 return TimeSpan.Zero;
 202
 203                         return LocalTimeZone.GetUtcOffset (dateTime);
 204                 }
 205
 206                 public override bool IsDaylightSavingTime (DateTime dateTime)
 207                 {
 208                         if (dateTime.Kind == DateTimeKind.Utc)
 209                                 return false;
 210
 211                         return LocalTimeZone.IsDaylightSavingTime (dateTime);
 212                 }
 213         }
 214 }