mcs/class/corlib/System/TimeZoneInfo.cs

   1
   2 /*
   3  * System.TimeZoneInfo
   4  *
   5  * Author(s)
   6  *      Stephane Delcroix <stephane@delcroix.org>
   7  *
   8  * Copyright 2011 Xamarin Inc.
   9  *
  10  * Permission is hereby granted, free of charge, to any person obtaining
  11  * a copy of this software and associated documentation files (the
  12  * "Software"), to deal in the Software without restriction, including
  13  * without limitation the rights to use, copy, modify, merge, publish,
  14  * distribute, sublicense, and/or sell copies of the Software, and to
  15  * permit persons to whom the Software is furnished to do so, subject to
  16  * the following conditions:
  17  *
  18  * The above copyright notice and this permission notice shall be
  19  * included in all copies or substantial portions of the Software.
  20  *
  21  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  22  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  23  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  24  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  25  * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  26  * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  27  * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  28  */
  29
  30 using System;
  31 using System.Runtime.CompilerServices;
  32 using System.Threading;
  33 using System.Collections.Generic;
  34 using System.Collections.ObjectModel;
  35 using System.Runtime.Serialization;
  36 using System.Text;
  37 using System.Globalization;
  38
  39 #if LIBC || MONODROID
  40 using System.IO;
  41 using Mono;
  42 #endif
  43
  44 using Microsoft.Win32;
  45
  46 namespace System
  47 {
  48 #if MOBILE
  49         [TypeForwardedFrom (Consts.AssemblySystem_Core)]
  50 #else
  51         [TypeForwardedFrom (Consts.AssemblySystemCore_3_5)]
  52 #endif
  53         [SerializableAttribute]
  54         public
  55         sealed partial class TimeZoneInfo : IEquatable<TimeZoneInfo>, ISerializable, IDeserializationCallback
  56         {
  57                 TimeSpan baseUtcOffset;
  58                 public TimeSpan BaseUtcOffset {
  59                         get { return baseUtcOffset; }
  60                 }
  61
  62                 string daylightDisplayName;
  63                 public string DaylightName {
  64                         get {
  65                                 return supportsDaylightSavingTime
  66                                         ? daylightDisplayName
  67                                         : string.Empty;
  68                         }
  69                 }
  70
  71                 string displayName;
  72                 public string DisplayName {
  73                         get { return displayName; }
  74                 }
  75
  76                 string id;
  77                 public string Id {
  78                         get { return id; }
  79                 }
  80
  81                 static TimeZoneInfo local;
  82                 public static TimeZoneInfo Local {
  83                         get {
  84                                 var l = local;
  85                                 if (l == null) {
  86                                         l = CreateLocal ();
  87                                         if (l == null)
  88                                                 throw new TimeZoneNotFoundException ();
  89
  90                                         if (Interlocked.CompareExchange (ref local, l, null) != null)
  91                                                 l = local;
  92                                 }
  93
  94                                 return l;
  95                         }
  96                 }
  97
  98                 /*
  99                         TimeZone transitions are stored when there is a change on the base offset.
 100                 */
 101                 private List<KeyValuePair<DateTime, TimeType>> transitions;
 102
 103                 static TimeZoneInfo CreateLocal ()
 104                 {
 105 #if MONODROID
 106                         return AndroidTimeZones.Local;
 107 #elif MONOTOUCH
 108                         using (Stream stream = GetMonoTouchData (null)) {
 109                                 return BuildFromStream ("Local", stream);
 110                         }
 111 #else
 112 #if !NET_2_1
 113                         if (IsWindows && LocalZoneKey != null) {
 114                                 string name = (string)LocalZoneKey.GetValue ("TimeZoneKeyName");
 115                                 if (name == null)
 116                                         name = (string)LocalZoneKey.GetValue ("StandardName"); // windows xp
 117                                 name = TrimSpecial (name);
 118                                 if (name != null)
 119                                         return TimeZoneInfo.FindSystemTimeZoneById (name);
 120                         }
 121 #endif
 122
 123                         var tz = Environment.GetEnvironmentVariable ("TZ");
 124                         if (tz != null) {
 125                                 if (tz == String.Empty)
 126                                         return Utc;
 127                                 try {
 128                                         return FindSystemTimeZoneByFileName (tz, Path.Combine (TimeZoneDirectory, tz));
 129                                 } catch {
 130                                         return Utc;
 131                                 }
 132                         }
 133
 134                         try {
 135                                 return FindSystemTimeZoneByFileName ("Local", "/etc/localtime");
 136                         } catch {
 137                                 try {
 138                                         return FindSystemTimeZoneByFileName ("Local", Path.Combine (TimeZoneDirectory, "localtime"));
 139                                 } catch {
 140                                         return null;
 141                                 }
 142                         }
 143 #endif
 144                 }
 145
 146                 string standardDisplayName;
 147                 public string StandardName {
 148                         get { return standardDisplayName; }
 149                 }
 150
 151                 bool supportsDaylightSavingTime;
 152                 public bool SupportsDaylightSavingTime {
 153                         get  { return supportsDaylightSavingTime; }
 154                 }
 155
 156                 static TimeZoneInfo utc;
 157                 public static TimeZoneInfo Utc {
 158                         get {
 159                                 if (utc == null)
 160                                         utc = CreateCustomTimeZone ("UTC", new TimeSpan (0), "UTC", "UTC");
 161                                 return utc;
 162                         }
 163                 }
 164 #if LIBC
 165                 static string timeZoneDirectory;
 166                 static string TimeZoneDirectory {
 167                         get {
 168                                 if (timeZoneDirectory == null)
 169                                         timeZoneDirectory = "/usr/share/zoneinfo";
 170                                 return timeZoneDirectory;
 171                         }
 172                         set {
 173                                 ClearCachedData ();
 174                                 timeZoneDirectory = value;
 175                         }
 176                 }
 177 #endif
 178                 private AdjustmentRule [] adjustmentRules;
 179
 180 #if !NET_2_1
 181                 /// <summary>
 182                 /// Determine whether windows of not (taken Stephane Delcroix's code)
 183                 /// </summary>
 184                 private static bool IsWindows
 185                 {
 186                         get {
 187                                 int platform = (int) Environment.OSVersion.Platform;
 188                                 return ((platform != 4) && (platform != 6) && (platform != 128));
 189                         }
 190                 }
 191
 192                 /// <summary>
 193                 /// Needed to trim misc garbage in MS registry keys
 194                 /// </summary>
 195                 private static string TrimSpecial (string str)
 196                 {
 197                         if (str == null)
 198                                 return str;
 199                         var Istart = 0;
 200                         while (Istart < str.Length && !char.IsLetterOrDigit(str[Istart])) Istart++;
 201                         var Iend = str.Length - 1;
 202                         while (Iend > Istart && !char.IsLetterOrDigit(str[Iend])) Iend--;
 203
 204                         return str.Substring (Istart, Iend-Istart+1);
 205                 }
 206
 207                 static RegistryKey timeZoneKey;
 208                 static RegistryKey TimeZoneKey {
 209                         get {
 210                                 if (timeZoneKey != null)
 211                                         return timeZoneKey;
 212                                 if (!IsWindows)
 213                                         return null;
 214
 215                                 return timeZoneKey = Registry.LocalMachine.OpenSubKey (
 216                                         "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones",
 217                                         false);
 218                         }
 219                 }
 220
 221                 static RegistryKey localZoneKey;
 222                 static RegistryKey LocalZoneKey {
 223                         get {
 224                                 if (localZoneKey != null)
 225                                         return localZoneKey;
 226
 227                                 if (!IsWindows)
 228                                         return null;
 229
 230                                 return localZoneKey = Registry.LocalMachine.OpenSubKey (
 231                                         "SYSTEM\\CurrentControlSet\\Control\\TimeZoneInformation", false);
 232                         }
 233                 }
 234 #endif
 235
 236                 public static void ClearCachedData ()
 237                 {
 238                         local = null;
 239                         utc = null;
 240                         systemTimeZones = null;
 241                 }
 242
 243                 public static DateTime ConvertTime (DateTime dateTime, TimeZoneInfo destinationTimeZone)
 244                 {
 245                         return ConvertTime (dateTime, dateTime.Kind == DateTimeKind.Utc ? TimeZoneInfo.Utc : TimeZoneInfo.Local, destinationTimeZone);
 246                 }
 247
 248                 public static DateTime ConvertTime (DateTime dateTime, TimeZoneInfo sourceTimeZone, TimeZoneInfo destinationTimeZone)
 249                 {
 250                         if (sourceTimeZone == null)
 251                                 throw new ArgumentNullException ("sourceTimeZone");
 252
 253                         if (destinationTimeZone == null)
 254                                 throw new ArgumentNullException ("destinationTimeZone");
 255
 256                         if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone != TimeZoneInfo.Local)
 257                                 throw new ArgumentException ("Kind property of dateTime is Local but the sourceTimeZone does not equal TimeZoneInfo.Local");
 258
 259                         if (dateTime.Kind == DateTimeKind.Utc && sourceTimeZone != TimeZoneInfo.Utc)
 260                                 throw new ArgumentException ("Kind property of dateTime is Utc but the sourceTimeZone does not equal TimeZoneInfo.Utc");
 261
 262                         if (sourceTimeZone.IsInvalidTime (dateTime))
 263                                 throw new ArgumentException ("dateTime parameter is an invalid time");
 264
 265                         if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone == TimeZoneInfo.Local && destinationTimeZone == TimeZoneInfo.Local)
 266                                 return dateTime;
 267
 268                         DateTime utc = ConvertTimeToUtc (dateTime, sourceTimeZone);
 269
 270                         if (destinationTimeZone != TimeZoneInfo.Utc) {
 271                                 utc = ConvertTimeFromUtc (utc, destinationTimeZone);
 272                                 if (dateTime.Kind == DateTimeKind.Unspecified)
 273                                         return DateTime.SpecifyKind (utc, DateTimeKind.Unspecified);
 274                         }
 275
 276                         return utc;
 277                 }
 278
 279                 public static DateTimeOffset ConvertTime(DateTimeOffset dateTimeOffset, TimeZoneInfo destinationTimeZone)
 280                 {
 281                         if (destinationTimeZone == null)
 282                                 throw new ArgumentNullException("destinationTimeZone");
 283
 284                         var utcDateTime = dateTimeOffset.UtcDateTime;
 285
 286                         bool isDst;
 287                         var utcOffset =  destinationTimeZone.GetUtcOffset(utcDateTime, out isDst);
 288
 289                         return new DateTimeOffset(DateTime.SpecifyKind(utcDateTime, DateTimeKind.Unspecified) + utcOffset, utcOffset);
 290                 }
 291
 292                 public static DateTime ConvertTimeBySystemTimeZoneId (DateTime dateTime, string destinationTimeZoneId)
 293                 {
 294                         return ConvertTime (dateTime, FindSystemTimeZoneById (destinationTimeZoneId));
 295                 }
 296
 297                 public static DateTime ConvertTimeBySystemTimeZoneId (DateTime dateTime, string sourceTimeZoneId, string destinationTimeZoneId)
 298                 {
 299                         return ConvertTime (dateTime, FindSystemTimeZoneById (sourceTimeZoneId), FindSystemTimeZoneById (destinationTimeZoneId));
 300                 }
 301
 302                 public static DateTimeOffset ConvertTimeBySystemTimeZoneId (DateTimeOffset dateTimeOffset, string destinationTimeZoneId)
 303                 {
 304                         return ConvertTime (dateTimeOffset, FindSystemTimeZoneById (destinationTimeZoneId));
 305                 }
 306
 307                 private DateTime ConvertTimeFromUtc (DateTime dateTime)
 308                 {
 309                         if (dateTime.Kind == DateTimeKind.Local)
 310                                 throw new ArgumentException ("Kind property of dateTime is Local");
 311
 312                         if (this == TimeZoneInfo.Utc)
 313                                 return DateTime.SpecifyKind (dateTime, DateTimeKind.Utc);
 314
 315                         var utcOffset = GetUtcOffset (dateTime);
 316
 317                         var kind = (this == TimeZoneInfo.Local)? DateTimeKind.Local : DateTimeKind.Unspecified;
 318
 319                         return DateTime.SpecifyKind (dateTime + utcOffset, kind);
 320                 }
 321
 322                 public static DateTime ConvertTimeFromUtc (DateTime dateTime, TimeZoneInfo destinationTimeZone)
 323                 {
 324                         if (destinationTimeZone == null)
 325                                 throw new ArgumentNullException ("destinationTimeZone");
 326
 327                         return destinationTimeZone.ConvertTimeFromUtc (dateTime);
 328                 }
 329
 330                 public static DateTime ConvertTimeToUtc (DateTime dateTime)
 331                 {
 332                         if (dateTime.Kind == DateTimeKind.Utc)
 333                                 return dateTime;
 334
 335                         return ConvertTimeToUtc (dateTime, TimeZoneInfo.Local);
 336                 }
 337
 338                 static internal DateTime ConvertTimeToUtc(DateTime dateTime, TimeZoneInfoOptions flags)
 339                 {
 340                         return ConvertTimeToUtc (dateTime, TimeZoneInfo.Local, flags);
 341                 }
 342
 343                 public static DateTime ConvertTimeToUtc (DateTime dateTime, TimeZoneInfo sourceTimeZone)
 344                 {
 345                         return ConvertTimeToUtc (dateTime, sourceTimeZone, TimeZoneInfoOptions.None);
 346                 }
 347
 348                 static DateTime ConvertTimeToUtc (DateTime dateTime, TimeZoneInfo sourceTimeZone, TimeZoneInfoOptions flags)
 349                 {
 350                         if ((flags & TimeZoneInfoOptions.NoThrowOnInvalidTime) == 0) {
 351                                 if (sourceTimeZone == null)
 352                                         throw new ArgumentNullException ("sourceTimeZone");
 353
 354                                 if (dateTime.Kind == DateTimeKind.Utc && sourceTimeZone != TimeZoneInfo.Utc)
 355                                         throw new ArgumentException ("Kind property of dateTime is Utc but the sourceTimeZone does not equal TimeZoneInfo.Utc");
 356
 357                                 if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone != TimeZoneInfo.Local)
 358                                         throw new ArgumentException ("Kind property of dateTime is Local but the sourceTimeZone does not equal TimeZoneInfo.Local");
 359
 360                                 if (sourceTimeZone.IsInvalidTime (dateTime))
 361                                         throw new ArgumentException ("dateTime parameter is an invalid time");
 362                         }
 363
 364                         if (dateTime.Kind == DateTimeKind.Utc)
 365                                 return dateTime;
 366
 367                         bool isDst;
 368                         var utcOffset = sourceTimeZone.GetUtcOffset (dateTime, out isDst);
 369
 370                         return DateTime.SpecifyKind (dateTime - utcOffset, DateTimeKind.Utc);
 371                 }
 372
 373                 static internal TimeSpan GetDateTimeNowUtcOffsetFromUtc(DateTime time, out Boolean isAmbiguousLocalDst)
 374                 {
 375                         bool isDaylightSavings;
 376                         return GetUtcOffsetFromUtc(time, TimeZoneInfo.Local, out isDaylightSavings, out isAmbiguousLocalDst);
 377                 }
 378
 379                 public static TimeZoneInfo CreateCustomTimeZone (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName)
 380                 {
 381                         return CreateCustomTimeZone (id, baseUtcOffset, displayName, standardDisplayName, null, null, true);
 382                 }
 383
 384                 public static TimeZoneInfo CreateCustomTimeZone (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules)
 385                 {
 386                         return CreateCustomTimeZone (id, baseUtcOffset, displayName, standardDisplayName, daylightDisplayName, adjustmentRules, false);
 387                 }
 388
 389                 public static TimeZoneInfo CreateCustomTimeZone ( string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules, bool disableDaylightSavingTime)
 390                 {
 391                         return new TimeZoneInfo (id, baseUtcOffset, displayName, standardDisplayName, daylightDisplayName, adjustmentRules, disableDaylightSavingTime);
 392                 }
 393
 394                 public override bool Equals (object obj)
 395                 {
 396                         return Equals (obj as TimeZoneInfo);
 397                 }
 398
 399                 public bool Equals (TimeZoneInfo other)
 400                 {
 401                         if (other == null)
 402                                 return false;
 403
 404                         return other.Id == this.Id && HasSameRules (other);
 405                 }
 406
 407                 public static TimeZoneInfo FindSystemTimeZoneById (string id)
 408                 {
 409                         //FIXME: this method should check for cached values in systemTimeZones
 410                         if (id == null)
 411                                 throw new ArgumentNullException ("id");
 412 #if !NET_2_1
 413                         if (TimeZoneKey != null)
 414                         {
 415                                 if (id == "Coordinated Universal Time")
 416                                         id = "UTC"; //windows xp exception for "StandardName" property
 417                                 RegistryKey key = TimeZoneKey.OpenSubKey (id, false);
 418                                 if (key == null)
 419                                         throw new TimeZoneNotFoundException ();
 420                                 return FromRegistryKey(id, key);
 421                         }
 422 #endif
 423                         // Local requires special logic that already exists in the Local property (bug #326)
 424                         if (id == "Local")
 425                                 return Local;
 426 #if MONOTOUCH
 427                         using (Stream stream = GetMonoTouchData (id)) {
 428                                 return BuildFromStream (id, stream);
 429                         }
 430 #elif MONODROID
 431                         var timeZoneInfo = AndroidTimeZones.GetTimeZone (id, id);
 432                         if (timeZoneInfo == null)
 433                                 throw new TimeZoneNotFoundException ();
 434                         return timeZoneInfo;
 435 #elif LIBC
 436                         string filepath = Path.Combine (TimeZoneDirectory, id);
 437                         return FindSystemTimeZoneByFileName (id, filepath);
 438 #else
 439                         throw new NotImplementedException ();
 440 #endif
 441                 }
 442
 443 #if LIBC
 444                 private static TimeZoneInfo FindSystemTimeZoneByFileName (string id, string filepath)
 445                 {
 446                         if (!File.Exists (filepath))
 447                                 throw new TimeZoneNotFoundException ();
 448
 449                         using (FileStream stream = File.OpenRead (filepath)) {
 450                                 return BuildFromStream (id, stream);
 451                         }
 452                 }
 453 #endif
 454 #if LIBC || MONOTOUCH
 455                 const int BUFFER_SIZE = 16384; //Big enough for any tz file (on Oct 2008, all tz files are under 10k)
 456
 457                 private static TimeZoneInfo BuildFromStream (string id, Stream stream)
 458                 {
 459                         byte [] buffer = new byte [BUFFER_SIZE];
 460                         int length = stream.Read (buffer, 0, BUFFER_SIZE);
 461
 462                         if (!ValidTZFile (buffer, length))
 463                                 throw new InvalidTimeZoneException ("TZ file too big for the buffer");
 464
 465                         try {
 466                                 return ParseTZBuffer (id, buffer, length);
 467                         } catch (Exception e) {
 468                                 throw new InvalidTimeZoneException (e.Message);
 469                         }
 470                 }
 471 #endif
 472
 473 #if !NET_2_1
 474                 private static TimeZoneInfo FromRegistryKey (string id, RegistryKey key)
 475                 {
 476                         byte [] reg_tzi = (byte []) key.GetValue ("TZI");
 477
 478                         if (reg_tzi == null)
 479                                 throw new InvalidTimeZoneException ();
 480
 481                         int bias = BitConverter.ToInt32 (reg_tzi, 0);
 482                         TimeSpan baseUtcOffset = new TimeSpan (0, -bias, 0);
 483
 484                         string display_name = (string) key.GetValue ("Display");
 485                         string standard_name = (string) key.GetValue ("Std");
 486                         string daylight_name = (string) key.GetValue ("Dlt");
 487
 488                         List<AdjustmentRule> adjustmentRules = new List<AdjustmentRule> ();
 489
 490                         RegistryKey dst_key = key.OpenSubKey ("Dynamic DST", false);
 491                         if (dst_key != null) {
 492                                 int first_year = (int) dst_key.GetValue ("FirstEntry");
 493                                 int last_year = (int) dst_key.GetValue ("LastEntry");
 494                                 int year;
 495
 496                                 for (year=first_year; year<=last_year; year++) {
 497                                         byte [] dst_tzi = (byte []) dst_key.GetValue (year.ToString ());
 498                                         if (dst_tzi != null) {
 499                                                 int start_year = year == first_year ? 1 : year;
 500                                                 int end_year = year == last_year ? 9999 : year;
 501                                                 ParseRegTzi(adjustmentRules, start_year, end_year, dst_tzi);
 502                                         }
 503                                 }
 504                         }
 505                         else
 506                                 ParseRegTzi(adjustmentRules, 1, 9999, reg_tzi);
 507
 508                         return CreateCustomTimeZone (id, baseUtcOffset, display_name, standard_name, daylight_name, ValidateRules (adjustmentRules).ToArray ());
 509                 }
 510
 511                 private static void ParseRegTzi (List<AdjustmentRule> adjustmentRules, int start_year, int end_year, byte [] buffer)
 512                 {
 513                         //int standard_bias = BitConverter.ToInt32 (buffer, 4); /* not sure how to handle this */
 514                         int daylight_bias = BitConverter.ToInt32 (buffer, 8);
 515
 516                         int standard_year = BitConverter.ToInt16 (buffer, 12);
 517                         int standard_month = BitConverter.ToInt16 (buffer, 14);
 518                         int standard_dayofweek = BitConverter.ToInt16 (buffer, 16);
 519                         int standard_day = BitConverter.ToInt16 (buffer, 18);
 520                         int standard_hour = BitConverter.ToInt16 (buffer, 20);
 521                         int standard_minute = BitConverter.ToInt16 (buffer, 22);
 522                         int standard_second = BitConverter.ToInt16 (buffer, 24);
 523                         int standard_millisecond = BitConverter.ToInt16 (buffer, 26);
 524
 525                         int daylight_year = BitConverter.ToInt16 (buffer, 28);
 526                         int daylight_month = BitConverter.ToInt16 (buffer, 30);
 527                         int daylight_dayofweek = BitConverter.ToInt16 (buffer, 32);
 528                         int daylight_day = BitConverter.ToInt16 (buffer, 34);
 529                         int daylight_hour = BitConverter.ToInt16 (buffer, 36);
 530                         int daylight_minute = BitConverter.ToInt16 (buffer, 38);
 531                         int daylight_second = BitConverter.ToInt16 (buffer, 40);
 532                         int daylight_millisecond = BitConverter.ToInt16 (buffer, 42);
 533
 534                         if (standard_month == 0 || daylight_month == 0)
 535                                 return;
 536
 537                         DateTime start_date;
 538                         DateTime start_timeofday = new DateTime (1, 1, 1, daylight_hour, daylight_minute, daylight_second, daylight_millisecond);
 539                         TransitionTime start_transition_time;
 540
 541                         if (daylight_year == 0) {
 542                                 start_date = new DateTime (start_year, 1, 1);
 543                                 start_transition_time = TransitionTime.CreateFloatingDateRule (
 544                                         start_timeofday, daylight_month, daylight_day,
 545                                         (DayOfWeek) daylight_dayofweek);
 546                         }
 547                         else {
 548                                 start_date = new DateTime (daylight_year, daylight_month, daylight_day,
 549                                         daylight_hour, daylight_minute, daylight_second, daylight_millisecond);
 550                                 start_transition_time = TransitionTime.CreateFixedDateRule (
 551                                         start_timeofday, daylight_month, daylight_day);
 552                         }
 553
 554                         DateTime end_date;
 555                         DateTime end_timeofday = new DateTime (1, 1, 1, standard_hour, standard_minute, standard_second, standard_millisecond);
 556                         TransitionTime end_transition_time;
 557
 558                         if (standard_year == 0) {
 559                                 end_date = new DateTime (end_year, 12, 31);
 560                                 end_transition_time = TransitionTime.CreateFloatingDateRule (
 561                                         end_timeofday, standard_month, standard_day,
 562                                         (DayOfWeek) standard_dayofweek);
 563                         }
 564                         else {
 565                                 end_date = new DateTime (standard_year, standard_month, standard_day,
 566                                         standard_hour, standard_minute, standard_second, standard_millisecond);
 567                                 end_transition_time = TransitionTime.CreateFixedDateRule (
 568                                         end_timeofday, standard_month, standard_day);
 569                         }
 570
 571                         TimeSpan daylight_delta = new TimeSpan(0, -daylight_bias, 0);
 572
 573                         adjustmentRules.Add (AdjustmentRule.CreateAdjustmentRule (
 574                                 start_date, end_date, daylight_delta,
 575                                 start_transition_time, end_transition_time));
 576                 }
 577 #endif
 578
 579                 public AdjustmentRule [] GetAdjustmentRules ()
 580                 {
 581                         if (!supportsDaylightSavingTime)
 582                                 return new AdjustmentRule [0];
 583                         else
 584                                 return (AdjustmentRule []) adjustmentRules.Clone ();
 585                 }
 586
 587                 public TimeSpan [] GetAmbiguousTimeOffsets (DateTime dateTime)
 588                 {
 589                         if (!IsAmbiguousTime (dateTime))
 590                                 throw new ArgumentException ("dateTime is not an ambiguous time");
 591
 592                         AdjustmentRule rule = GetApplicableRule (dateTime);
 593                         if (rule != null)
 594                                 return new TimeSpan[] {baseUtcOffset, baseUtcOffset + rule.DaylightDelta};
 595                         else
 596                                 return new TimeSpan[] {baseUtcOffset, baseUtcOffset};
 597                 }
 598
 599                 public TimeSpan [] GetAmbiguousTimeOffsets (DateTimeOffset dateTimeOffset)
 600                 {
 601                         if (!IsAmbiguousTime (dateTimeOffset))
 602                                 throw new ArgumentException ("dateTimeOffset is not an ambiguous time");
 603
 604                         throw new NotImplementedException ();
 605                 }
 606
 607                 public override int GetHashCode ()
 608                 {
 609                         int hash_code = Id.GetHashCode ();
 610                         foreach (AdjustmentRule rule in GetAdjustmentRules ())
 611                                 hash_code ^= rule.GetHashCode ();
 612                         return hash_code;
 613                 }
 614
 615                 void ISerializable.GetObjectData (SerializationInfo info, StreamingContext context)
 616                 {
 617                         if (info == null)
 618                                 throw new ArgumentNullException ("info");
 619                         info.AddValue ("Id", id);
 620                         info.AddValue ("DisplayName", displayName);
 621                         info.AddValue ("StandardName", standardDisplayName);
 622                         info.AddValue ("DaylightName", daylightDisplayName);
 623                         info.AddValue ("BaseUtcOffset", baseUtcOffset);
 624                         info.AddValue ("AdjustmentRules", adjustmentRules);
 625                         info.AddValue ("SupportsDaylightSavingTime", SupportsDaylightSavingTime);
 626                 }
 627
 628                 //FIXME: change this to a generic Dictionary and allow caching for FindSystemTimeZoneById
 629                 private static List<TimeZoneInfo> systemTimeZones;
 630                 public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones ()
 631                 {
 632                         if (systemTimeZones == null) {
 633                                 systemTimeZones = new List<TimeZoneInfo> ();
 634 #if !NET_2_1
 635                                 if (TimeZoneKey != null) {
 636                                         foreach (string id in TimeZoneKey.GetSubKeyNames ()) {
 637                                                 try {
 638                                                         systemTimeZones.Add (FindSystemTimeZoneById (id));
 639                                                 } catch {}
 640                                         }
 641
 642                                         return new ReadOnlyCollection<TimeZoneInfo> (systemTimeZones);
 643                                 }
 644 #endif
 645 #if MONODROID
 646                         foreach (string id in AndroidTimeZones.GetAvailableIds ()) {
 647                                 var tz = AndroidTimeZones.GetTimeZone (id, id);
 648                                 if (tz != null)
 649                                         systemTimeZones.Add (tz);
 650                         }
 651 #elif MONOTOUCH
 652                                 if (systemTimeZones.Count == 0) {
 653                                         foreach (string name in GetMonoTouchNames ()) {
 654                                                 using (Stream stream = GetMonoTouchData (name, false)) {
 655                                                         if (stream == null)
 656                                                                 continue;
 657                                                         systemTimeZones.Add (BuildFromStream (name, stream));
 658                                                 }
 659                                         }
 660                                 }
 661 #elif LIBC
 662                                 string[] continents = new string [] {"Africa", "America", "Antarctica", "Arctic", "Asia", "Atlantic", "Brazil", "Canada", "Chile", "Europe", "Indian", "Mexico", "Mideast", "Pacific", "US"};
 663                                 foreach (string continent in continents) {
 664                                         try {
 665                                                 foreach (string zonepath in Directory.GetFiles (Path.Combine (TimeZoneDirectory, continent))) {
 666                                                         try {
 667                                                                 string id = String.Format ("{0}/{1}", continent, Path.GetFileName (zonepath));
 668                                                                 systemTimeZones.Add (FindSystemTimeZoneById (id));
 669                                                         } catch (ArgumentNullException) {
 670                                                         } catch (TimeZoneNotFoundException) {
 671                                                         } catch (InvalidTimeZoneException) {
 672                                                         } catch (Exception) {
 673                                                                 throw;
 674                                                         }
 675                                                 }
 676                                         } catch {}
 677                                 }
 678 #else
 679                                 throw new NotImplementedException ("This method is not implemented for this platform");
 680 #endif
 681                         }
 682                         return new ReadOnlyCollection<TimeZoneInfo> (systemTimeZones);
 683                 }
 684
 685                 public TimeSpan GetUtcOffset (DateTime dateTime)
 686                 {
 687                         bool isDST;
 688                         return GetUtcOffset (dateTime, out isDST);
 689                 }
 690
 691                 public TimeSpan GetUtcOffset (DateTimeOffset dateTimeOffset)
 692                 {
 693                         throw new NotImplementedException ();
 694                 }
 695
 696                 private TimeSpan GetUtcOffset (DateTime dateTime, out bool isDST)
 697                 {
 698                         isDST = false;
 699
 700                         TimeZoneInfo tz = this;
 701                         if (dateTime.Kind == DateTimeKind.Utc)
 702                                 tz = TimeZoneInfo.Utc;
 703
 704                         if (dateTime.Kind == DateTimeKind.Local)
 705                                 tz = TimeZoneInfo.Local;
 706
 707                         bool isTzDst;
 708                         var tzOffset = GetUtcOffset (dateTime, tz, out isTzDst);
 709
 710                         if (tz == this) {
 711                                 isDST = isTzDst;
 712                                 return tzOffset;
 713                         }
 714
 715                         var utcTicks = dateTime.Ticks - tzOffset.Ticks;
 716                         if (utcTicks < 0 || utcTicks > DateTime.MaxValue.Ticks)
 717                                 return BaseUtcOffset;
 718
 719                         var utcDateTime = new DateTime (utcTicks, DateTimeKind.Utc);
 720
 721                         return GetUtcOffset (utcDateTime, this, out isDST);
 722                 }
 723
 724                 private static TimeSpan GetUtcOffset (DateTime dateTime, TimeZoneInfo tz, out bool isDST)
 725                 {
 726                         if (dateTime.Kind == DateTimeKind.Local && tz != TimeZoneInfo.Local)
 727                                 throw new Exception ();
 728
 729                         isDST = false;
 730
 731                         if (tz == TimeZoneInfo.Utc)
 732                                 return TimeSpan.Zero;
 733
 734                         TimeSpan offset;
 735                         if (tz.TryGetTransitionOffset(dateTime, out offset, out isDST))
 736                                 return offset;
 737
 738                         if (dateTime.Kind == DateTimeKind.Utc) {
 739                                 var utcRule = tz.GetApplicableRule (dateTime);
 740                                 if (utcRule != null && tz.IsInDST (utcRule, dateTime)) {
 741                                         isDST = true;
 742                                         return tz.BaseUtcOffset + utcRule.DaylightDelta;
 743                                 }
 744
 745                                 return tz.BaseUtcOffset;
 746                         }
 747
 748                         var stdTicks = dateTime.Ticks - tz.BaseUtcOffset.Ticks;
 749                         if (stdTicks < 0 || stdTicks > DateTime.MaxValue.Ticks)
 750                                 return tz.BaseUtcOffset;
 751
 752                         var stdUtcDateTime = new DateTime (stdTicks, DateTimeKind.Utc);
 753                         var tzRule = tz.GetApplicableRule (stdUtcDateTime);
 754
 755                         DateTime dstUtcDateTime = DateTime.MinValue;
 756                         if (tzRule != null) {
 757                                 var dstTicks = stdUtcDateTime.Ticks - tzRule.DaylightDelta.Ticks;
 758                                 if (dstTicks < 0 || dstTicks > DateTime.MaxValue.Ticks)
 759                                         return tz.BaseUtcOffset;
 760
 761                                 dstUtcDateTime = new DateTime (dstTicks, DateTimeKind.Utc);
 762                         }
 763
 764                         if (tzRule != null && tz.IsInDST (tzRule, stdUtcDateTime) && tz.IsInDST (tzRule, dstUtcDateTime)) {
 765                                 isDST = true;
 766                                 return tz.BaseUtcOffset + tzRule.DaylightDelta;
 767                         }
 768
 769                         return tz.BaseUtcOffset;
 770                 }
 771
 772                 public bool HasSameRules (TimeZoneInfo other)
 773                 {
 774                         if (other == null)
 775                                 throw new ArgumentNullException ("other");
 776
 777                         if ((this.adjustmentRules == null) != (other.adjustmentRules == null))
 778                                 return false;
 779
 780                         if (this.adjustmentRules == null)
 781                                 return true;
 782
 783                         if (this.BaseUtcOffset != other.BaseUtcOffset)
 784                                 return false;
 785
 786                         if (this.adjustmentRules.Length != other.adjustmentRules.Length)
 787                                 return false;
 788
 789                         for (int i = 0; i < adjustmentRules.Length; i++) {
 790                                 if (! (this.adjustmentRules [i]).Equals (other.adjustmentRules [i]))
 791                                         return false;
 792                         }
 793
 794                         return true;
 795                 }
 796
 797                 public bool IsAmbiguousTime (DateTime dateTime)
 798                 {
 799                         if (dateTime.Kind == DateTimeKind.Local && IsInvalidTime (dateTime))
 800                                 throw new ArgumentException ("Kind is Local and time is Invalid");
 801
 802                         if (this == TimeZoneInfo.Utc)
 803                                 return false;
 804
 805                         if (dateTime.Kind == DateTimeKind.Utc)
 806                                 dateTime = ConvertTimeFromUtc (dateTime);
 807
 808                         if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local)
 809                                 dateTime = ConvertTime (dateTime, TimeZoneInfo.Local, this);
 810
 811                         AdjustmentRule rule = GetApplicableRule (dateTime);
 812                         if (rule != null) {
 813                                 DateTime tpoint = TransitionPoint (rule.DaylightTransitionEnd, dateTime.Year);
 814                                 if (dateTime > tpoint - rule.DaylightDelta  && dateTime <= tpoint)
 815                                         return true;
 816                         }
 817
 818                         return false;
 819                 }
 820
 821                 public bool IsAmbiguousTime (DateTimeOffset dateTimeOffset)
 822                 {
 823                         throw new NotImplementedException ();
 824                 }
 825
 826                 private bool IsInDST (AdjustmentRule rule, DateTime dateTime)
 827                 {
 828                         // Check whether we're in the dateTime year's DST period
 829                         if (IsInDSTForYear (rule, dateTime, dateTime.Year))
 830                                 return true;
 831
 832                         // We might be in the dateTime previous year's DST period
 833                         return IsInDSTForYear (rule, dateTime, dateTime.Year - 1);
 834                 }
 835
 836                 bool IsInDSTForYear (AdjustmentRule rule, DateTime dateTime, int year)
 837                 {
 838                         DateTime DST_start = TransitionPoint (rule.DaylightTransitionStart, year);
 839                         DateTime DST_end = TransitionPoint (rule.DaylightTransitionEnd, year + ((rule.DaylightTransitionStart.Month < rule.DaylightTransitionEnd.Month) ? 0 : 1));
 840                         if (dateTime.Kind == DateTimeKind.Utc) {
 841                                 DST_start -= BaseUtcOffset;
 842                                 DST_end -= (BaseUtcOffset + rule.DaylightDelta);
 843                         }
 844
 845                         return (dateTime >= DST_start && dateTime < DST_end);
 846                 }
 847
 848                 public bool IsDaylightSavingTime (DateTime dateTime)
 849                 {
 850                         if (dateTime.Kind == DateTimeKind.Local && IsInvalidTime (dateTime))
 851                                 throw new ArgumentException ("dateTime is invalid and Kind is Local");
 852
 853                         if (this == TimeZoneInfo.Utc)
 854                                 return false;
 855
 856                         if (!SupportsDaylightSavingTime)
 857                                 return false;
 858
 859                         bool isDst;
 860                         GetUtcOffset (dateTime, out isDst);
 861
 862                         return isDst;
 863                 }
 864
 865                 internal bool IsDaylightSavingTime (DateTime dateTime, TimeZoneInfoOptions flags)
 866                 {
 867                         return IsDaylightSavingTime (dateTime);
 868                 }
 869
 870                 public bool IsDaylightSavingTime (DateTimeOffset dateTimeOffset)
 871                 {
 872                         throw new NotImplementedException ();
 873                 }
 874
 875                 void IDeserializationCallback.OnDeserialization (object sender)
 876                 {
 877                         try {
 878                                         TimeZoneInfo.Validate (id, baseUtcOffset, adjustmentRules);
 879                                 } catch (ArgumentException ex) {
 880                                         throw new SerializationException ("invalid serialization data", ex);
 881                                 }
 882                 }
 883
 884                 private static void Validate (string id, TimeSpan baseUtcOffset, AdjustmentRule [] adjustmentRules)
 885                 {
 886                         if (id == null)
 887                                 throw new ArgumentNullException ("id");
 888
 889                         if (id == String.Empty)
 890                                 throw new ArgumentException ("id parameter is an empty string");
 891
 892                         if (baseUtcOffset.Ticks % TimeSpan.TicksPerMinute != 0)
 893                                 throw new ArgumentException ("baseUtcOffset parameter does not represent a whole number of minutes");
 894
 895                         if (baseUtcOffset > new TimeSpan (14, 0, 0) || baseUtcOffset < new TimeSpan (-14, 0, 0))
 896                                 throw new ArgumentOutOfRangeException ("baseUtcOffset parameter is greater than 14 hours or less than -14 hours");
 897
 898 #if STRICT
 899                         if (id.Length > 32)
 900                                 throw new ArgumentException ("id parameter shouldn't be longer than 32 characters");
 901 #endif
 902
 903                         if (adjustmentRules != null && adjustmentRules.Length != 0) {
 904                                 AdjustmentRule prev = null;
 905                                 foreach (AdjustmentRule current in adjustmentRules) {
 906                                         if (current == null)
 907                                                 throw new InvalidTimeZoneException ("one or more elements in adjustmentRules are null");
 908
 909                                         if ((baseUtcOffset + current.DaylightDelta < new TimeSpan (-14, 0, 0)) ||
 910                                                         (baseUtcOffset + current.DaylightDelta > new TimeSpan (14, 0, 0)))
 911                                                 throw new InvalidTimeZoneException ("Sum of baseUtcOffset and DaylightDelta of one or more object in adjustmentRules array is greater than 14 or less than -14 hours;");
 912
 913                                         if (prev != null && prev.DateStart > current.DateStart)
 914                                                 throw new InvalidTimeZoneException ("adjustment rules specified in adjustmentRules parameter are not in chronological order");
 915
 916                                         if (prev != null && prev.DateEnd > current.DateStart)
 917                                                 throw new InvalidTimeZoneException ("some adjustment rules in the adjustmentRules parameter overlap");
 918
 919                                         if (prev != null && prev.DateEnd == current.DateStart)
 920                                                 throw new InvalidTimeZoneException ("a date can have multiple adjustment rules applied to it");
 921
 922                                         prev = current;
 923                                 }
 924                         }
 925                 }
 926
 927                 public override string ToString ()
 928                 {
 929                         return DisplayName;
 930                 }
 931
 932                 private TimeZoneInfo (SerializationInfo info, StreamingContext context)
 933                 {
 934                         if (info == null)
 935                                 throw new ArgumentNullException ("info");
 936                         id = (string) info.GetValue ("Id", typeof (string));
 937                         displayName = (string) info.GetValue ("DisplayName", typeof (string));
 938                         standardDisplayName = (string) info.GetValue ("StandardName", typeof (string));
 939                         daylightDisplayName = (string) info.GetValue ("DaylightName", typeof (string));
 940                         baseUtcOffset = (TimeSpan) info.GetValue ("BaseUtcOffset", typeof (TimeSpan));
 941                         adjustmentRules = (TimeZoneInfo.AdjustmentRule []) info.GetValue ("AdjustmentRules", typeof (TimeZoneInfo.AdjustmentRule []));
 942                         supportsDaylightSavingTime = (bool) info.GetValue ("SupportsDaylightSavingTime", typeof (bool));
 943                 }
 944
 945                 private TimeZoneInfo (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules, bool disableDaylightSavingTime)
 946                 {
 947                         if (id == null)
 948                                 throw new ArgumentNullException ("id");
 949
 950                         if (id == String.Empty)
 951                                 throw new ArgumentException ("id parameter is an empty string");
 952
 953                         if (baseUtcOffset.Ticks % TimeSpan.TicksPerMinute != 0)
 954                                 throw new ArgumentException ("baseUtcOffset parameter does not represent a whole number of minutes");
 955
 956                         if (baseUtcOffset > new TimeSpan (14, 0, 0) || baseUtcOffset < new TimeSpan (-14, 0, 0))
 957                                 throw new ArgumentOutOfRangeException ("baseUtcOffset parameter is greater than 14 hours or less than -14 hours");
 958
 959 #if STRICT
 960                         if (id.Length > 32)
 961                                 throw new ArgumentException ("id parameter shouldn't be longer than 32 characters");
 962 #endif
 963
 964                         bool supportsDaylightSavingTime = !disableDaylightSavingTime;
 965
 966                         if (adjustmentRules != null && adjustmentRules.Length != 0) {
 967                                 AdjustmentRule prev = null;
 968                                 foreach (AdjustmentRule current in adjustmentRules) {
 969                                         if (current == null)
 970                                                 throw new InvalidTimeZoneException ("one or more elements in adjustmentRules are null");
 971
 972                                         if ((baseUtcOffset + current.DaylightDelta < new TimeSpan (-14, 0, 0)) ||
 973                                                         (baseUtcOffset + current.DaylightDelta > new TimeSpan (14, 0, 0)))
 974                                                 throw new InvalidTimeZoneException ("Sum of baseUtcOffset and DaylightDelta of one or more object in adjustmentRules array is greater than 14 or less than -14 hours;");
 975
 976                                         if (prev != null && prev.DateStart > current.DateStart)
 977                                                 throw new InvalidTimeZoneException ("adjustment rules specified in adjustmentRules parameter are not in chronological order");
 978
 979                                         if (prev != null && prev.DateEnd > current.DateStart)
 980                                                 throw new InvalidTimeZoneException ("some adjustment rules in the adjustmentRules parameter overlap");
 981
 982                                         if (prev != null && prev.DateEnd == current.DateStart)
 983                                                 throw new InvalidTimeZoneException ("a date can have multiple adjustment rules applied to it");
 984
 985                                         prev = current;
 986                                 }
 987                         } else {
 988                                 supportsDaylightSavingTime = false;
 989                         }
 990
 991                         this.id = id;
 992                         this.baseUtcOffset = baseUtcOffset;
 993                         this.displayName = displayName ?? id;
 994                         this.standardDisplayName = standardDisplayName ?? id;
 995                         this.daylightDisplayName = daylightDisplayName;
 996                         this.supportsDaylightSavingTime = supportsDaylightSavingTime;
 997                         this.adjustmentRules = adjustmentRules;
 998                 }
 999
1000                 private AdjustmentRule GetApplicableRule (DateTime dateTime)
1001                 {
1002                         //Applicable rules are in standard time
1003                         DateTime date = dateTime;
1004
1005                         if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local)
1006                                 date = date.ToUniversalTime () + BaseUtcOffset;
1007                         else if (dateTime.Kind == DateTimeKind.Utc && this != TimeZoneInfo.Utc)
1008                                 date = date + BaseUtcOffset;
1009
1010                         // get the date component of the datetime
1011                         date = date.Date;
1012
1013                         if (adjustmentRules != null) {
1014                                 foreach (AdjustmentRule rule in adjustmentRules) {
1015                                         if (rule.DateStart > date)
1016                                                 return null;
1017                                         if (rule.DateEnd < date)
1018                                                 continue;
1019                                         return rule;
1020                                 }
1021                         }
1022                         return null;
1023                 }
1024
1025                 private bool TryGetTransitionOffset (DateTime dateTime, out TimeSpan offset,out bool isDst)
1026                 {
1027                         offset = BaseUtcOffset;
1028                         isDst = false;
1029
1030                         if (transitions == null)
1031                                 return false;
1032
1033                         //Transitions are in UTC
1034                         DateTime date = dateTime;
1035
1036                         if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local) {
1037                                 var ticks = date.ToUniversalTime ().Ticks + BaseUtcOffset.Ticks;
1038                                 if (ticks < DateTime.MinValue.Ticks || ticks > DateTime.MaxValue.Ticks)
1039                                         return false;
1040
1041                                 date = new DateTime (ticks, DateTimeKind.Utc);
1042                         }
1043
1044                         if (dateTime.Kind != DateTimeKind.Utc) {
1045                                 var ticks = date.Ticks - BaseUtcOffset.Ticks;
1046                                 if (ticks < DateTime.MinValue.Ticks || ticks > DateTime.MaxValue.Ticks)
1047                                         return false;
1048
1049                                 date = new DateTime (ticks, DateTimeKind.Utc);
1050                         }
1051
1052                         for (var i =  transitions.Count - 1; i >= 0; i--) {
1053                                 var pair = transitions [i];
1054                                 DateTime ttime = pair.Key;
1055                                 TimeType ttype = pair.Value;
1056
1057                                 if (ttime > date)
1058                                         continue;
1059
1060                                 offset =  new TimeSpan (0, 0, ttype.Offset);
1061                                 isDst = ttype.IsDst;
1062
1063                                 return true;
1064                         }
1065
1066                         return false;
1067                 }
1068
1069                 private static DateTime TransitionPoint (TransitionTime transition, int year)
1070                 {
1071                         if (transition.IsFixedDateRule)
1072                                 return new DateTime (year, transition.Month, transition.Day) + transition.TimeOfDay.TimeOfDay;
1073
1074                         DayOfWeek first = (new DateTime (year, transition.Month, 1)).DayOfWeek;
1075                         int day = 1 + (transition.Week - 1) * 7 + (transition.DayOfWeek - first + 7) % 7;
1076                         if (day >  DateTime.DaysInMonth (year, transition.Month))
1077                                 day -= 7;
1078                         if (day < 1)
1079                                 day += 7;
1080                         return new DateTime (year, transition.Month, day) + transition.TimeOfDay.TimeOfDay;
1081                 }
1082
1083                 static List<AdjustmentRule> ValidateRules (List<AdjustmentRule> adjustmentRules)
1084                 {
1085                         AdjustmentRule prev = null;
1086                         foreach (AdjustmentRule current in adjustmentRules.ToArray ()) {
1087                                 if (prev != null && prev.DateEnd > current.DateStart) {
1088                                         adjustmentRules.Remove (current);
1089                                 }
1090                                 prev = current;
1091                         }
1092                         return adjustmentRules;
1093                 }
1094
1095 #if LIBC || MONODROID
1096                 private static bool ValidTZFile (byte [] buffer, int length)
1097                 {
1098                         StringBuilder magic = new StringBuilder ();
1099
1100                         for (int i = 0; i < 4; i++)
1101                                 magic.Append ((char)buffer [i]);
1102
1103                         if (magic.ToString () != "TZif")
1104                                 return false;
1105
1106                         if (length >= BUFFER_SIZE)
1107                                 return false;
1108
1109                         return true;
1110                 }
1111
1112                 static int SwapInt32 (int i)
1113                 {
1114                         return (((i >> 24) & 0xff)
1115                                 | ((i >> 8) & 0xff00)
1116                                 | ((i << 8) & 0xff0000)
1117                                 | ((i << 24)));
1118                 }
1119
1120                 static int ReadBigEndianInt32 (byte [] buffer, int start)
1121                 {
1122                         int i = BitConverter.ToInt32 (buffer, start);
1123                         if (!BitConverter.IsLittleEndian)
1124                                 return i;
1125
1126                         return SwapInt32 (i);
1127                 }
1128
1129                 private static TimeZoneInfo ParseTZBuffer (string id, byte [] buffer, int length)
1130                 {
1131                         //Reading the header. 4 bytes for magic, 16 are reserved
1132                         int ttisgmtcnt = ReadBigEndianInt32 (buffer, 20);
1133                         int ttisstdcnt = ReadBigEndianInt32 (buffer, 24);
1134                         int leapcnt = ReadBigEndianInt32 (buffer, 28);
1135                         int timecnt = ReadBigEndianInt32 (buffer, 32);
1136                         int typecnt = ReadBigEndianInt32 (buffer, 36);
1137                         int charcnt = ReadBigEndianInt32 (buffer, 40);
1138
1139                         if (length < 44 + timecnt * 5 + typecnt * 6 + charcnt + leapcnt * 8 + ttisstdcnt + ttisgmtcnt)
1140                                 throw new InvalidTimeZoneException ();
1141
1142                         Dictionary<int, string> abbreviations = ParseAbbreviations (buffer, 44 + 4 * timecnt + timecnt + 6 * typecnt, charcnt);
1143                         Dictionary<int, TimeType> time_types = ParseTimesTypes (buffer, 44 + 4 * timecnt + timecnt, typecnt, abbreviations);
1144                         List<KeyValuePair<DateTime, TimeType>> transitions = ParseTransitions (buffer, 44, timecnt, time_types);
1145
1146                         if (time_types.Count == 0)
1147                                 throw new InvalidTimeZoneException ();
1148
1149                         if (time_types.Count == 1 && ((TimeType)time_types[0]).IsDst)
1150                                 throw new InvalidTimeZoneException ();
1151
1152                         TimeSpan baseUtcOffset = new TimeSpan (0);
1153                         TimeSpan dstDelta = new TimeSpan (0);
1154                         string standardDisplayName = null;
1155                         string daylightDisplayName = null;
1156                         bool dst_observed = false;
1157                         DateTime dst_start = DateTime.MinValue;
1158                         List<AdjustmentRule> adjustmentRules = new List<AdjustmentRule> ();
1159                         bool storeTransition = false;
1160
1161                         for (int i = 0; i < transitions.Count; i++) {
1162                                 var pair = transitions [i];
1163                                 DateTime ttime = pair.Key;
1164                                 TimeType ttype = pair.Value;
1165                                 if (!ttype.IsDst) {
1166                                         if (standardDisplayName != ttype.Name)
1167                                                 standardDisplayName = ttype.Name;
1168                                         if (baseUtcOffset.TotalSeconds != ttype.Offset) {
1169                                                 baseUtcOffset = new TimeSpan (0, 0, ttype.Offset);
1170                                                 if (adjustmentRules.Count > 0) // We ignore AdjustmentRules but store transitions.
1171                                                         storeTransition = true;
1172                                                 adjustmentRules = new List<AdjustmentRule> ();
1173                                                 dst_observed = false;
1174                                         }
1175                                         if (dst_observed) {
1176                                                 //FIXME: check additional fields for this:
1177                                                 //most of the transitions are expressed in GMT
1178                                                 dst_start += baseUtcOffset;
1179                                                 DateTime dst_end = ttime + baseUtcOffset + dstDelta;
1180
1181                                                 //some weird timezone (America/Phoenix) have end dates on Jan 1st
1182                                                 if (dst_end.Date == new DateTime (dst_end.Year, 1, 1) && dst_end.Year > dst_start.Year)
1183                                                         dst_end -= new TimeSpan (24, 0, 0);
1184
1185                                                 DateTime dateStart, dateEnd;
1186                                                 if (dst_start.Month < 7)
1187                                                         dateStart = new DateTime (dst_start.Year, 1, 1);
1188                                                 else
1189                                                         dateStart = new DateTime (dst_start.Year, 7, 1);
1190
1191                                                 if (dst_end.Month >= 7)
1192                                                         dateEnd = new DateTime (dst_end.Year, 12, 31);
1193                                                 else
1194                                                         dateEnd = new DateTime (dst_end.Year, 6, 30);
1195
1196
1197                                                 TransitionTime transition_start = TransitionTime.CreateFixedDateRule (new DateTime (1, 1, 1) + dst_start.TimeOfDay, dst_start.Month, dst_start.Day);
1198                                                 TransitionTime transition_end = TransitionTime.CreateFixedDateRule (new DateTime (1, 1, 1) + dst_end.TimeOfDay, dst_end.Month, dst_end.Day);
1199                                                 if  (transition_start != transition_end) //y, that happened in Argentina in 1943-1946
1200                                                         adjustmentRules.Add (AdjustmentRule.CreateAdjustmentRule (dateStart, dateEnd, dstDelta, transition_start, transition_end));
1201                                         }
1202                                         dst_observed = false;
1203                                 } else {
1204                                         if (daylightDisplayName != ttype.Name)
1205                                                 daylightDisplayName = ttype.Name;
1206                                         if (dstDelta.TotalSeconds != ttype.Offset - baseUtcOffset.TotalSeconds)
1207                                                 dstDelta = new TimeSpan(0, 0, ttype.Offset) - baseUtcOffset;
1208
1209                                         dst_start = ttime;
1210                                         dst_observed = true;
1211                                 }
1212                         }
1213
1214                         TimeZoneInfo tz;
1215                         if (adjustmentRules.Count == 0 && !storeTransition) {
1216                                 TimeType t = (TimeType)time_types [0];
1217                                 if (standardDisplayName == null) {
1218                                         standardDisplayName = t.Name;
1219                                         baseUtcOffset = new TimeSpan (0, 0, t.Offset);
1220                                 }
1221                                 tz = CreateCustomTimeZone (id, baseUtcOffset, id, standardDisplayName);
1222                         } else {
1223                                 tz = CreateCustomTimeZone (id, baseUtcOffset, id, standardDisplayName, daylightDisplayName, ValidateRules (adjustmentRules).ToArray ());
1224                         }
1225
1226                         if (storeTransition)
1227                                 tz.transitions = transitions;
1228
1229                         return tz;
1230                 }
1231
1232                 static Dictionary<int, string> ParseAbbreviations (byte [] buffer, int index, int count)
1233                 {
1234                         var abbrevs = new Dictionary<int, string> ();
1235                         int abbrev_index = 0;
1236                         var sb = new StringBuilder ();
1237                         for (int i = 0; i < count; i++) {
1238                                 char c = (char) buffer [index + i];
1239                                 if (c != '\0')
1240                                         sb.Append (c);
1241                                 else {
1242                                         abbrevs.Add (abbrev_index, sb.ToString ());
1243                                         //Adding all the substrings too, as it seems to be used, at least for Africa/Windhoek
1244                                         for (int j = 1; j < sb.Length; j++)
1245                                                 abbrevs.Add (abbrev_index + j, sb.ToString (j, sb.Length - j));
1246                                         abbrev_index = i + 1;
1247                                         sb = new StringBuilder ();
1248                                 }
1249                         }
1250                         return abbrevs;
1251                 }
1252
1253                 static Dictionary<int, TimeType> ParseTimesTypes (byte [] buffer, int index, int count, Dictionary<int, string> abbreviations)
1254                 {
1255                         var types = new Dictionary<int, TimeType> (count);
1256                         for (int i = 0; i < count; i++) {
1257                                 int offset = ReadBigEndianInt32 (buffer, index + 6 * i);
1258                                 byte is_dst = buffer [index + 6 * i + 4];
1259                                 byte abbrev = buffer [index + 6 * i + 5];
1260                                 types.Add (i, new TimeType (offset, (is_dst != 0), abbreviations [(int)abbrev]));
1261                         }
1262                         return types;
1263                 }
1264
1265                 static List<KeyValuePair<DateTime, TimeType>> ParseTransitions (byte [] buffer, int index, int count, Dictionary<int, TimeType> time_types)
1266                 {
1267                         var list = new List<KeyValuePair<DateTime, TimeType>> (count);
1268                         for (int i = 0; i < count; i++) {
1269                                 int unixtime = ReadBigEndianInt32 (buffer, index + 4 * i);
1270                                 DateTime ttime = DateTimeFromUnixTime (unixtime);
1271                                 byte ttype = buffer [index + 4 * count + i];
1272                                 list.Add (new KeyValuePair<DateTime, TimeType> (ttime, time_types [(int)ttype]));
1273                         }
1274                         return list;
1275                 }
1276
1277                 static DateTime DateTimeFromUnixTime (long unix_time)
1278                 {
1279                         DateTime date_time = new DateTime (1970, 1, 1);
1280                         return date_time.AddSeconds (unix_time);
1281                 }
1282
1283 #region reference sources
1284         // Shortcut for TimeZoneInfo.Local.GetUtcOffset
1285         internal static TimeSpan GetLocalUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
1286         {
1287             bool dst;
1288             return Local.GetUtcOffset (dateTime, out dst);
1289         }
1290
1291         internal TimeSpan GetUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
1292         {
1293             bool dst;
1294             return GetUtcOffset (dateTime, out dst);
1295         }
1296
1297         // used by GetUtcOffsetFromUtc (DateTime.Now, DateTime.ToLocalTime) for max/min whole-day range checks
1298         private static DateTime s_maxDateOnly = new DateTime(9999, 12, 31);
1299         private static DateTime s_minDateOnly = new DateTime(1, 1, 2);
1300
1301         static internal TimeSpan GetUtcOffsetFromUtc (DateTime time, TimeZoneInfo zone, out Boolean isDaylightSavings, out Boolean isAmbiguousLocalDst)
1302         {
1303             isDaylightSavings = false;
1304             isAmbiguousLocalDst = false;
1305             TimeSpan baseOffset = zone.BaseUtcOffset;
1306             Int32 year;
1307             AdjustmentRule rule;
1308
1309             if (time > s_maxDateOnly) {
1310                 rule = zone.GetAdjustmentRuleForTime(DateTime.MaxValue);
1311                 year = 9999;
1312             }
1313             else if (time < s_minDateOnly) {
1314                 rule = zone.GetAdjustmentRuleForTime(DateTime.MinValue);
1315                 year = 1;
1316             }
1317             else {
1318                 DateTime targetTime = time + baseOffset;
1319                 year = time.Year;
1320                 rule = zone.GetAdjustmentRuleForTime(targetTime);
1321             }
1322
1323             if (rule != null) {
1324                 isDaylightSavings = GetIsDaylightSavingsFromUtc(time, year, zone.baseUtcOffset, rule, out isAmbiguousLocalDst);
1325                 baseOffset += (isDaylightSavings ? rule.DaylightDelta : TimeSpan.Zero /* */);
1326             }
1327
1328             return baseOffset;
1329         }
1330
1331         // assumes dateTime is in the current time zone's time
1332         private AdjustmentRule GetAdjustmentRuleForTime(DateTime dateTime) {
1333             if (adjustmentRules == null || adjustmentRules.Length == 0) {
1334                 return null;
1335             }
1336
1337 #if WINXP_AND_WIN2K3_SUPPORT
1338             // On pre-Vista versions of Windows if you run "cmd /c date" or "cmd /c time" to update the system time
1339             // the operating system doesn't pick up the correct time zone adjustment rule (it stays on the currently loaded rule).
1340             // We need to use the OS API data in this scenario instead of the loaded adjustment rules from the registry for
1341             // consistency.  Otherwise DateTime.Now might not match the time displayed in the system tray.
1342             if (!Environment.IsWindowsVistaOrAbove && s_cachedData.GetCorrespondingKind(this) == DateTimeKind.Local) {
1343                 return s_cachedData.GetOneYearLocalFromLocal(dateTime.Year).rule;
1344             }
1345 #endif
1346             // Only check the whole-date portion of the dateTime -
1347             // This is because the AdjustmentRule DateStart & DateEnd are stored as
1348             // Date-only values {4/2/2006 - 10/28/2006} but actually represent the
1349             // time span {4/2/2006@00:00:00.00000 - 10/28/2006@23:59:59.99999}
1350             DateTime date = dateTime.Date;
1351
1352             for (int i = 0; i < adjustmentRules.Length; i++) {
1353                 if (adjustmentRules[i].DateStart <= date && adjustmentRules[i].DateEnd >= date) {
1354                     return adjustmentRules[i];
1355                 }
1356             }
1357
1358             return null;
1359         }
1360
1361         //
1362         // GetIsDaylightSavingsFromUtc -
1363         //
1364         // Helper function that checks if a given dateTime is in Daylight Saving Time (DST)
1365         // This function assumes the dateTime is in UTC and AdjustmentRule is in a different time zone
1366         //
1367         static private Boolean GetIsDaylightSavingsFromUtc(DateTime time, Int32 Year, TimeSpan utc, AdjustmentRule rule, out Boolean isAmbiguousLocalDst) {
1368             isAmbiguousLocalDst = false;
1369
1370             if (rule == null) {
1371                 return false;
1372             }
1373
1374             // Get the daylight changes for the year of the specified time.
1375             TimeSpan offset = utc; /* */
1376             DaylightTime daylightTime = GetDaylightTime(Year, rule);
1377
1378             // The start and end times represent the range of universal times that are in DST for that year.
1379             // Within that there is an ambiguous hour, usually right at the end, but at the beginning in
1380             // the unusual case of a negative daylight savings delta.
1381             DateTime startTime = daylightTime.Start - offset;
1382             DateTime endTime = daylightTime.End - offset - rule.DaylightDelta; /* */
1383             DateTime ambiguousStart;
1384             DateTime ambiguousEnd;
1385             if (daylightTime.Delta.Ticks > 0) {
1386                 ambiguousStart = endTime - daylightTime.Delta;
1387                 ambiguousEnd = endTime;
1388             } else {
1389                 ambiguousStart = startTime;
1390                 ambiguousEnd = startTime - daylightTime.Delta;
1391             }
1392
1393             Boolean isDst = CheckIsDst(startTime, time, endTime);
1394
1395             // See if the resulting local time becomes ambiguous. This must be captured here or the
1396             // DateTime will not be able to round-trip back to UTC accurately.
1397             if (isDst) {
1398                 isAmbiguousLocalDst = (time >= ambiguousStart && time < ambiguousEnd);
1399
1400                 if (!isAmbiguousLocalDst && ambiguousStart.Year != ambiguousEnd.Year) {
1401                     // there exists an extreme corner case where the start or end period is on a year boundary and
1402                     // because of this the comparison above might have been performed for a year-early or a year-later
1403                     // than it should have been.
1404                     DateTime ambiguousStartModified;
1405                     DateTime ambiguousEndModified;
1406                     try {
1407                         ambiguousStartModified = ambiguousStart.AddYears(1);
1408                         ambiguousEndModified   = ambiguousEnd.AddYears(1);
1409                         isAmbiguousLocalDst = (time >= ambiguousStart && time < ambiguousEnd);
1410                     }
1411                     catch (ArgumentOutOfRangeException) {}
1412
1413                     if (!isAmbiguousLocalDst) {
1414                         try {
1415                             ambiguousStartModified = ambiguousStart.AddYears(-1);
1416                             ambiguousEndModified   = ambiguousEnd.AddYears(-1);
1417                             isAmbiguousLocalDst = (time >= ambiguousStart && time < ambiguousEnd);
1418                         }
1419                         catch (ArgumentOutOfRangeException) {}
1420                     }
1421
1422                 }
1423             }
1424
1425             return isDst;
1426         }
1427
1428
1429         static private Boolean CheckIsDst(DateTime startTime, DateTime time, DateTime endTime) {
1430             Boolean isDst;
1431
1432             int startTimeYear = startTime.Year;
1433             int endTimeYear = endTime.Year;
1434
1435             if (startTimeYear != endTimeYear) {
1436                 endTime = endTime.AddYears(startTimeYear - endTimeYear);
1437             }
1438
1439             int timeYear = time.Year;
1440
1441             if (startTimeYear != timeYear) {
1442                 time = time.AddYears(startTimeYear - timeYear);
1443             }
1444
1445             if (startTime > endTime) {
1446                 // In southern hemisphere, the daylight saving time starts later in the year, and ends in the beginning of next year.
1447                 // Note, the summer in the southern hemisphere begins late in the year.
1448                 isDst = (time < endTime || time >= startTime);
1449             }
1450             else {
1451                 // In northern hemisphere, the daylight saving time starts in the middle of the year.
1452                 isDst = (time >= startTime && time < endTime);
1453             }
1454             return isDst;
1455         }
1456
1457         //
1458         // GetDaylightTime -
1459         //
1460         // Helper function that returns a DaylightTime from a year and AdjustmentRule
1461         //
1462         static private DaylightTime GetDaylightTime(Int32 year, AdjustmentRule rule) {
1463             TimeSpan delta = rule.DaylightDelta;
1464             DateTime startTime = TransitionTimeToDateTime(year, rule.DaylightTransitionStart);
1465             DateTime endTime = TransitionTimeToDateTime(year, rule.DaylightTransitionEnd);
1466             return new DaylightTime(startTime, endTime, delta);
1467         }
1468
1469         //
1470         // TransitionTimeToDateTime -
1471         //
1472         // Helper function that converts a year and TransitionTime into a DateTime
1473         //
1474         static private DateTime TransitionTimeToDateTime(Int32 year, TransitionTime transitionTime) {
1475             DateTime value;
1476             DateTime timeOfDay = transitionTime.TimeOfDay;
1477
1478             if (transitionTime.IsFixedDateRule) {
1479                 // create a DateTime from the passed in year and the properties on the transitionTime
1480
1481                 // if the day is out of range for the month then use the last day of the month
1482                 Int32 day = DateTime.DaysInMonth(year, transitionTime.Month);
1483
1484                 value = new DateTime(year, transitionTime.Month, (day < transitionTime.Day) ? day : transitionTime.Day,
1485                             timeOfDay.Hour, timeOfDay.Minute, timeOfDay.Second, timeOfDay.Millisecond);
1486             }
1487             else {
1488                 if (transitionTime.Week <= 4) {
1489                     //
1490                     // Get the (transitionTime.Week)th Sunday.
1491                     //
1492                     value = new DateTime(year, transitionTime.Month, 1,
1493                             timeOfDay.Hour, timeOfDay.Minute, timeOfDay.Second, timeOfDay.Millisecond);
1494
1495                     int dayOfWeek = (int)value.DayOfWeek;
1496                     int delta = (int)transitionTime.DayOfWeek - dayOfWeek;
1497                     if (delta < 0) {
1498                         delta += 7;
1499                     }
1500                     delta += 7 * (transitionTime.Week - 1);
1501
1502                     if (delta > 0) {
1503                         value = value.AddDays(delta);
1504                     }
1505                 }
1506                 else {
1507                     //
1508                     // If TransitionWeek is greater than 4, we will get the last week.
1509                     //
1510                     Int32 daysInMonth = DateTime.DaysInMonth(year, transitionTime.Month);
1511                     value = new DateTime(year, transitionTime.Month, daysInMonth,
1512                             timeOfDay.Hour, timeOfDay.Minute, timeOfDay.Second, timeOfDay.Millisecond);
1513
1514                     // This is the day of week for the last day of the month.
1515                     int dayOfWeek = (int)value.DayOfWeek;
1516                     int delta = dayOfWeek - (int)transitionTime.DayOfWeek;
1517                     if (delta < 0) {
1518                         delta += 7;
1519                     }
1520
1521                     if (delta > 0) {
1522                         value = value.AddDays(-delta);
1523                     }
1524                 }
1525             }
1526             return value;
1527         }
1528
1529         //
1530         // IsInvalidTime -
1531         //
1532         // returns true when dateTime falls into a "hole in time".
1533         //
1534         public Boolean IsInvalidTime(DateTime dateTime) {
1535             Boolean isInvalid = false;
1536
1537             if ( (dateTime.Kind == DateTimeKind.Unspecified)
1538             ||   (dateTime.Kind == DateTimeKind.Local && this == Local) ) {
1539
1540                 // only check Unspecified and (Local when this TimeZoneInfo instance is Local)
1541                 AdjustmentRule rule = GetAdjustmentRuleForTime(dateTime);
1542
1543
1544                 if (rule != null) {
1545                     DaylightTime daylightTime = GetDaylightTime(dateTime.Year, rule);
1546                     isInvalid = GetIsInvalidTime(dateTime, rule, daylightTime);
1547                 }
1548                 else {
1549                     isInvalid = false;
1550                 }
1551             }
1552
1553             return isInvalid;
1554         }
1555
1556         //
1557         // GetIsInvalidTime -
1558         //
1559         // Helper function that checks if a given DateTime is in an invalid time ("time hole")
1560         // A "time hole" occurs at a DST transition point when time jumps forward;
1561         // For example, in Pacific Standard Time on Sunday, April 2, 2006 time jumps from
1562         // 1:59:59.9999999 to 3AM.  The time range 2AM to 2:59:59.9999999AM is the "time hole".
1563         // A "time hole" is not limited to only occurring at the start of DST, and may occur at
1564         // the end of DST as well.
1565         //
1566         static private Boolean GetIsInvalidTime(DateTime time, AdjustmentRule rule, DaylightTime daylightTime) {
1567             Boolean isInvalid = false;
1568             if (rule == null || rule.DaylightDelta == TimeSpan.Zero) {
1569                 return isInvalid;
1570             }
1571
1572             DateTime startInvalidTime;
1573             DateTime endInvalidTime;
1574
1575             // if at DST start we transition forward in time then there is an ambiguous time range at the DST end
1576             if (rule.DaylightDelta < TimeSpan.Zero) {
1577                 startInvalidTime = daylightTime.End;
1578                 endInvalidTime = daylightTime.End - rule.DaylightDelta; /* */
1579             }
1580             else {
1581                 startInvalidTime = daylightTime.Start;
1582                 endInvalidTime = daylightTime.Start + rule.DaylightDelta; /* */
1583             }
1584
1585             isInvalid = (time >= startInvalidTime && time < endInvalidTime);
1586
1587             if (!isInvalid && startInvalidTime.Year != endInvalidTime.Year) {
1588                 // there exists an extreme corner case where the start or end period is on a year boundary and
1589                 // because of this the comparison above might have been performed for a year-early or a year-later
1590                 // than it should have been.
1591                 DateTime startModifiedInvalidTime;
1592                 DateTime endModifiedInvalidTime;
1593                 try {
1594                     startModifiedInvalidTime = startInvalidTime.AddYears(1);
1595                     endModifiedInvalidTime   = endInvalidTime.AddYears(1);
1596                     isInvalid = (time >= startModifiedInvalidTime && time < endModifiedInvalidTime);
1597                 }
1598                 catch (ArgumentOutOfRangeException) {}
1599
1600                 if (!isInvalid) {
1601                     try {
1602                         startModifiedInvalidTime = startInvalidTime.AddYears(-1);
1603                         endModifiedInvalidTime  = endInvalidTime.AddYears(-1);
1604                         isInvalid = (time >= startModifiedInvalidTime && time < endModifiedInvalidTime);
1605                     }
1606                     catch (ArgumentOutOfRangeException) {}
1607                 }
1608             }
1609             return isInvalid;
1610         }
1611 #endregion
1612         }
1613
1614         struct TimeType {
1615                 public readonly int Offset;
1616                 public readonly bool IsDst;
1617                 public string Name;
1618
1619                 public TimeType (int offset, bool is_dst, string abbrev)
1620                 {
1621                         this.Offset = offset;
1622                         this.IsDst = is_dst;
1623                         this.Name = abbrev;
1624                 }
1625
1626                 public override string ToString ()
1627                 {
1628                         return "offset: " + Offset + "s, is_dst: " + IsDst + ", zone name: " + Name;
1629                 }
1630 #else
1631         }
1632 #endif
1633         }
1634 }