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                 private static bool TryAddTicks (DateTime date, long ticks, out DateTime result, DateTimeKind kind = DateTimeKind.Unspecified)
 237                 {
 238                         var resultTicks = date.Ticks + ticks;
 239                         if (resultTicks < DateTime.MinValue.Ticks || resultTicks > DateTime.MaxValue.Ticks) {
 240                                 result =  default (DateTime);
 241                                 return false;
 242                         }
 243
 244                         result = new DateTime (resultTicks, kind);
 245                         return true;
 246                 }
 247
 248                 public static void ClearCachedData ()
 249                 {
 250                         local = null;
 251                         utc = null;
 252                         systemTimeZones = null;
 253                 }
 254
 255                 public static DateTime ConvertTime (DateTime dateTime, TimeZoneInfo destinationTimeZone)
 256                 {
 257                         return ConvertTime (dateTime, dateTime.Kind == DateTimeKind.Utc ? TimeZoneInfo.Utc : TimeZoneInfo.Local, destinationTimeZone);
 258                 }
 259
 260                 public static DateTime ConvertTime (DateTime dateTime, TimeZoneInfo sourceTimeZone, TimeZoneInfo destinationTimeZone)
 261                 {
 262                         if (sourceTimeZone == null)
 263                                 throw new ArgumentNullException ("sourceTimeZone");
 264
 265                         if (destinationTimeZone == null)
 266                                 throw new ArgumentNullException ("destinationTimeZone");
 267
 268                         if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone != TimeZoneInfo.Local)
 269                                 throw new ArgumentException ("Kind property of dateTime is Local but the sourceTimeZone does not equal TimeZoneInfo.Local");
 270
 271                         if (dateTime.Kind == DateTimeKind.Utc && sourceTimeZone != TimeZoneInfo.Utc)
 272                                 throw new ArgumentException ("Kind property of dateTime is Utc but the sourceTimeZone does not equal TimeZoneInfo.Utc");
 273
 274                         if (sourceTimeZone.IsInvalidTime (dateTime))
 275                                 throw new ArgumentException ("dateTime parameter is an invalid time");
 276
 277                         if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone == TimeZoneInfo.Local && destinationTimeZone == TimeZoneInfo.Local)
 278                                 return dateTime;
 279
 280                         DateTime utc = ConvertTimeToUtc (dateTime, sourceTimeZone);
 281
 282                         if (destinationTimeZone != TimeZoneInfo.Utc) {
 283                                 utc = ConvertTimeFromUtc (utc, destinationTimeZone);
 284                                 if (dateTime.Kind == DateTimeKind.Unspecified)
 285                                         return DateTime.SpecifyKind (utc, DateTimeKind.Unspecified);
 286                         }
 287
 288                         return utc;
 289                 }
 290
 291                 public static DateTimeOffset ConvertTime(DateTimeOffset dateTimeOffset, TimeZoneInfo destinationTimeZone)
 292                 {
 293                         if (destinationTimeZone == null)
 294                                 throw new ArgumentNullException("destinationTimeZone");
 295
 296                         var utcDateTime = dateTimeOffset.UtcDateTime;
 297
 298                         bool isDst;
 299                         var utcOffset =  destinationTimeZone.GetUtcOffset(utcDateTime, out isDst);
 300
 301                         return new DateTimeOffset(DateTime.SpecifyKind(utcDateTime, DateTimeKind.Unspecified) + utcOffset, utcOffset);
 302                 }
 303
 304                 public static DateTime ConvertTimeBySystemTimeZoneId (DateTime dateTime, string destinationTimeZoneId)
 305                 {
 306                         return ConvertTime (dateTime, FindSystemTimeZoneById (destinationTimeZoneId));
 307                 }
 308
 309                 public static DateTime ConvertTimeBySystemTimeZoneId (DateTime dateTime, string sourceTimeZoneId, string destinationTimeZoneId)
 310                 {
 311                         return ConvertTime (dateTime, FindSystemTimeZoneById (sourceTimeZoneId), FindSystemTimeZoneById (destinationTimeZoneId));
 312                 }
 313
 314                 public static DateTimeOffset ConvertTimeBySystemTimeZoneId (DateTimeOffset dateTimeOffset, string destinationTimeZoneId)
 315                 {
 316                         return ConvertTime (dateTimeOffset, FindSystemTimeZoneById (destinationTimeZoneId));
 317                 }
 318
 319                 private DateTime ConvertTimeFromUtc (DateTime dateTime)
 320                 {
 321                         if (dateTime.Kind == DateTimeKind.Local)
 322                                 throw new ArgumentException ("Kind property of dateTime is Local");
 323
 324                         if (this == TimeZoneInfo.Utc)
 325                                 return DateTime.SpecifyKind (dateTime, DateTimeKind.Utc);
 326
 327                         var utcOffset = GetUtcOffset (dateTime);
 328
 329                         var kind = (this == TimeZoneInfo.Local)? DateTimeKind.Local : DateTimeKind.Unspecified;
 330
 331                         DateTime result;
 332                         if (!TryAddTicks (dateTime, utcOffset.Ticks, out result, kind))
 333                                 return DateTime.SpecifyKind (DateTime.MaxValue, kind);
 334
 335                         return result;
 336                 }
 337
 338                 public static DateTime ConvertTimeFromUtc (DateTime dateTime, TimeZoneInfo destinationTimeZone)
 339                 {
 340                         if (destinationTimeZone == null)
 341                                 throw new ArgumentNullException ("destinationTimeZone");
 342
 343                         return destinationTimeZone.ConvertTimeFromUtc (dateTime);
 344                 }
 345
 346                 public static DateTime ConvertTimeToUtc (DateTime dateTime)
 347                 {
 348                         if (dateTime.Kind == DateTimeKind.Utc)
 349                                 return dateTime;
 350
 351                         return ConvertTimeToUtc (dateTime, TimeZoneInfo.Local);
 352                 }
 353
 354                 static internal DateTime ConvertTimeToUtc(DateTime dateTime, TimeZoneInfoOptions flags)
 355                 {
 356                         return ConvertTimeToUtc (dateTime, TimeZoneInfo.Local, flags);
 357                 }
 358
 359                 public static DateTime ConvertTimeToUtc (DateTime dateTime, TimeZoneInfo sourceTimeZone)
 360                 {
 361                         return ConvertTimeToUtc (dateTime, sourceTimeZone, TimeZoneInfoOptions.None);
 362                 }
 363
 364                 static DateTime ConvertTimeToUtc (DateTime dateTime, TimeZoneInfo sourceTimeZone, TimeZoneInfoOptions flags)
 365                 {
 366                         if ((flags & TimeZoneInfoOptions.NoThrowOnInvalidTime) == 0) {
 367                                 if (sourceTimeZone == null)
 368                                         throw new ArgumentNullException ("sourceTimeZone");
 369
 370                                 if (dateTime.Kind == DateTimeKind.Utc && sourceTimeZone != TimeZoneInfo.Utc)
 371                                         throw new ArgumentException ("Kind property of dateTime is Utc but the sourceTimeZone does not equal TimeZoneInfo.Utc");
 372
 373                                 if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone != TimeZoneInfo.Local)
 374                                         throw new ArgumentException ("Kind property of dateTime is Local but the sourceTimeZone does not equal TimeZoneInfo.Local");
 375
 376                                 if (sourceTimeZone.IsInvalidTime (dateTime))
 377                                         throw new ArgumentException ("dateTime parameter is an invalid time");
 378                         }
 379
 380                         if (dateTime.Kind == DateTimeKind.Utc)
 381                                 return dateTime;
 382
 383                         bool isDst;
 384                         var utcOffset = sourceTimeZone.GetUtcOffset (dateTime, out isDst);
 385
 386                         DateTime utcDateTime;
 387                         if (!TryAddTicks (dateTime, -utcOffset.Ticks, out utcDateTime, DateTimeKind.Utc))
 388                                 return DateTime.SpecifyKind (DateTime.MinValue, DateTimeKind.Utc);
 389
 390                         return utcDateTime;
 391                 }
 392
 393                 static internal TimeSpan GetDateTimeNowUtcOffsetFromUtc(DateTime time, out Boolean isAmbiguousLocalDst)
 394                 {
 395                         bool isDaylightSavings;
 396                         return GetUtcOffsetFromUtc(time, TimeZoneInfo.Local, out isDaylightSavings, out isAmbiguousLocalDst);
 397                 }
 398
 399                 public static TimeZoneInfo CreateCustomTimeZone (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName)
 400                 {
 401                         return CreateCustomTimeZone (id, baseUtcOffset, displayName, standardDisplayName, null, null, true);
 402                 }
 403
 404                 public static TimeZoneInfo CreateCustomTimeZone (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules)
 405                 {
 406                         return CreateCustomTimeZone (id, baseUtcOffset, displayName, standardDisplayName, daylightDisplayName, adjustmentRules, false);
 407                 }
 408
 409                 public static TimeZoneInfo CreateCustomTimeZone ( string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules, bool disableDaylightSavingTime)
 410                 {
 411                         return new TimeZoneInfo (id, baseUtcOffset, displayName, standardDisplayName, daylightDisplayName, adjustmentRules, disableDaylightSavingTime);
 412                 }
 413
 414                 public override bool Equals (object obj)
 415                 {
 416                         return Equals (obj as TimeZoneInfo);
 417                 }
 418
 419                 public bool Equals (TimeZoneInfo other)
 420                 {
 421                         if (other == null)
 422                                 return false;
 423
 424                         return other.Id == this.Id && HasSameRules (other);
 425                 }
 426
 427                 public static TimeZoneInfo FindSystemTimeZoneById (string id)
 428                 {
 429                         //FIXME: this method should check for cached values in systemTimeZones
 430                         if (id == null)
 431                                 throw new ArgumentNullException ("id");
 432 #if !NET_2_1
 433                         if (TimeZoneKey != null)
 434                         {
 435                                 if (id == "Coordinated Universal Time")
 436                                         id = "UTC"; //windows xp exception for "StandardName" property
 437                                 RegistryKey key = TimeZoneKey.OpenSubKey (id, false);
 438                                 if (key == null)
 439                                         throw new TimeZoneNotFoundException ();
 440                                 return FromRegistryKey(id, key);
 441                         }
 442 #endif
 443                         // Local requires special logic that already exists in the Local property (bug #326)
 444                         if (id == "Local")
 445                                 return Local;
 446 #if MONOTOUCH
 447                         using (Stream stream = GetMonoTouchData (id)) {
 448                                 return BuildFromStream (id, stream);
 449                         }
 450 #elif MONODROID
 451                         var timeZoneInfo = AndroidTimeZones.GetTimeZone (id, id);
 452                         if (timeZoneInfo == null)
 453                                 throw new TimeZoneNotFoundException ();
 454                         return timeZoneInfo;
 455 #elif LIBC
 456                         string filepath = Path.Combine (TimeZoneDirectory, id);
 457                         return FindSystemTimeZoneByFileName (id, filepath);
 458 #else
 459                         throw new NotImplementedException ();
 460 #endif
 461                 }
 462
 463 #if LIBC
 464                 private static TimeZoneInfo FindSystemTimeZoneByFileName (string id, string filepath)
 465                 {
 466                         if (!File.Exists (filepath))
 467                                 throw new TimeZoneNotFoundException ();
 468
 469                         using (FileStream stream = File.OpenRead (filepath)) {
 470                                 return BuildFromStream (id, stream);
 471                         }
 472                 }
 473 #endif
 474 #if LIBC || MONOTOUCH
 475                 const int BUFFER_SIZE = 16384; //Big enough for any tz file (on Oct 2008, all tz files are under 10k)
 476
 477                 private static TimeZoneInfo BuildFromStream (string id, Stream stream)
 478                 {
 479                         byte [] buffer = new byte [BUFFER_SIZE];
 480                         int length = stream.Read (buffer, 0, BUFFER_SIZE);
 481
 482                         if (!ValidTZFile (buffer, length))
 483                                 throw new InvalidTimeZoneException ("TZ file too big for the buffer");
 484
 485                         try {
 486                                 return ParseTZBuffer (id, buffer, length);
 487                         } catch (Exception e) {
 488                                 throw new InvalidTimeZoneException (e.Message);
 489                         }
 490                 }
 491 #endif
 492
 493 #if !NET_2_1
 494                 private static TimeZoneInfo FromRegistryKey (string id, RegistryKey key)
 495                 {
 496                         byte [] reg_tzi = (byte []) key.GetValue ("TZI");
 497
 498                         if (reg_tzi == null)
 499                                 throw new InvalidTimeZoneException ();
 500
 501                         int bias = BitConverter.ToInt32 (reg_tzi, 0);
 502                         TimeSpan baseUtcOffset = new TimeSpan (0, -bias, 0);
 503
 504                         string display_name = (string) key.GetValue ("Display");
 505                         string standard_name = (string) key.GetValue ("Std");
 506                         string daylight_name = (string) key.GetValue ("Dlt");
 507
 508                         List<AdjustmentRule> adjustmentRules = new List<AdjustmentRule> ();
 509
 510                         RegistryKey dst_key = key.OpenSubKey ("Dynamic DST", false);
 511                         if (dst_key != null) {
 512                                 int first_year = (int) dst_key.GetValue ("FirstEntry");
 513                                 int last_year = (int) dst_key.GetValue ("LastEntry");
 514                                 int year;
 515
 516                                 for (year=first_year; year<=last_year; year++) {
 517                                         byte [] dst_tzi = (byte []) dst_key.GetValue (year.ToString ());
 518                                         if (dst_tzi != null) {
 519                                                 int start_year = year == first_year ? 1 : year;
 520                                                 int end_year = year == last_year ? 9999 : year;
 521                                                 ParseRegTzi(adjustmentRules, start_year, end_year, dst_tzi);
 522                                         }
 523                                 }
 524                         }
 525                         else
 526                                 ParseRegTzi(adjustmentRules, 1, 9999, reg_tzi);
 527
 528                         return CreateCustomTimeZone (id, baseUtcOffset, display_name, standard_name, daylight_name, ValidateRules (adjustmentRules).ToArray ());
 529                 }
 530
 531                 private static void ParseRegTzi (List<AdjustmentRule> adjustmentRules, int start_year, int end_year, byte [] buffer)
 532                 {
 533                         //int standard_bias = BitConverter.ToInt32 (buffer, 4); /* not sure how to handle this */
 534                         int daylight_bias = BitConverter.ToInt32 (buffer, 8);
 535
 536                         int standard_year = BitConverter.ToInt16 (buffer, 12);
 537                         int standard_month = BitConverter.ToInt16 (buffer, 14);
 538                         int standard_dayofweek = BitConverter.ToInt16 (buffer, 16);
 539                         int standard_day = BitConverter.ToInt16 (buffer, 18);
 540                         int standard_hour = BitConverter.ToInt16 (buffer, 20);
 541                         int standard_minute = BitConverter.ToInt16 (buffer, 22);
 542                         int standard_second = BitConverter.ToInt16 (buffer, 24);
 543                         int standard_millisecond = BitConverter.ToInt16 (buffer, 26);
 544
 545                         int daylight_year = BitConverter.ToInt16 (buffer, 28);
 546                         int daylight_month = BitConverter.ToInt16 (buffer, 30);
 547                         int daylight_dayofweek = BitConverter.ToInt16 (buffer, 32);
 548                         int daylight_day = BitConverter.ToInt16 (buffer, 34);
 549                         int daylight_hour = BitConverter.ToInt16 (buffer, 36);
 550                         int daylight_minute = BitConverter.ToInt16 (buffer, 38);
 551                         int daylight_second = BitConverter.ToInt16 (buffer, 40);
 552                         int daylight_millisecond = BitConverter.ToInt16 (buffer, 42);
 553
 554                         if (standard_month == 0 || daylight_month == 0)
 555                                 return;
 556
 557                         DateTime start_date;
 558                         DateTime start_timeofday = new DateTime (1, 1, 1, daylight_hour, daylight_minute, daylight_second, daylight_millisecond);
 559                         TransitionTime start_transition_time;
 560
 561                         if (daylight_year == 0) {
 562                                 start_date = new DateTime (start_year, 1, 1);
 563                                 start_transition_time = TransitionTime.CreateFloatingDateRule (
 564                                         start_timeofday, daylight_month, daylight_day,
 565                                         (DayOfWeek) daylight_dayofweek);
 566                         }
 567                         else {
 568                                 start_date = new DateTime (daylight_year, daylight_month, daylight_day,
 569                                         daylight_hour, daylight_minute, daylight_second, daylight_millisecond);
 570                                 start_transition_time = TransitionTime.CreateFixedDateRule (
 571                                         start_timeofday, daylight_month, daylight_day);
 572                         }
 573
 574                         DateTime end_date;
 575                         DateTime end_timeofday = new DateTime (1, 1, 1, standard_hour, standard_minute, standard_second, standard_millisecond);
 576                         TransitionTime end_transition_time;
 577
 578                         if (standard_year == 0) {
 579                                 end_date = new DateTime (end_year, 12, 31);
 580                                 end_transition_time = TransitionTime.CreateFloatingDateRule (
 581                                         end_timeofday, standard_month, standard_day,
 582                                         (DayOfWeek) standard_dayofweek);
 583                         }
 584                         else {
 585                                 end_date = new DateTime (standard_year, standard_month, standard_day,
 586                                         standard_hour, standard_minute, standard_second, standard_millisecond);
 587                                 end_transition_time = TransitionTime.CreateFixedDateRule (
 588                                         end_timeofday, standard_month, standard_day);
 589                         }
 590
 591                         TimeSpan daylight_delta = new TimeSpan(0, -daylight_bias, 0);
 592
 593                         adjustmentRules.Add (AdjustmentRule.CreateAdjustmentRule (
 594                                 start_date, end_date, daylight_delta,
 595                                 start_transition_time, end_transition_time));
 596                 }
 597 #endif
 598
 599                 public AdjustmentRule [] GetAdjustmentRules ()
 600                 {
 601                         if (!supportsDaylightSavingTime)
 602                                 return new AdjustmentRule [0];
 603                         else
 604                                 return (AdjustmentRule []) adjustmentRules.Clone ();
 605                 }
 606
 607                 public TimeSpan [] GetAmbiguousTimeOffsets (DateTime dateTime)
 608                 {
 609                         if (!IsAmbiguousTime (dateTime))
 610                                 throw new ArgumentException ("dateTime is not an ambiguous time");
 611
 612                         AdjustmentRule rule = GetApplicableRule (dateTime);
 613                         if (rule != null)
 614                                 return new TimeSpan[] {baseUtcOffset, baseUtcOffset + rule.DaylightDelta};
 615                         else
 616                                 return new TimeSpan[] {baseUtcOffset, baseUtcOffset};
 617                 }
 618
 619                 public TimeSpan [] GetAmbiguousTimeOffsets (DateTimeOffset dateTimeOffset)
 620                 {
 621                         if (!IsAmbiguousTime (dateTimeOffset))
 622                                 throw new ArgumentException ("dateTimeOffset is not an ambiguous time");
 623
 624                         throw new NotImplementedException ();
 625                 }
 626
 627                 public override int GetHashCode ()
 628                 {
 629                         int hash_code = Id.GetHashCode ();
 630                         foreach (AdjustmentRule rule in GetAdjustmentRules ())
 631                                 hash_code ^= rule.GetHashCode ();
 632                         return hash_code;
 633                 }
 634
 635                 void ISerializable.GetObjectData (SerializationInfo info, StreamingContext context)
 636                 {
 637                         if (info == null)
 638                                 throw new ArgumentNullException ("info");
 639                         info.AddValue ("Id", id);
 640                         info.AddValue ("DisplayName", displayName);
 641                         info.AddValue ("StandardName", standardDisplayName);
 642                         info.AddValue ("DaylightName", daylightDisplayName);
 643                         info.AddValue ("BaseUtcOffset", baseUtcOffset);
 644                         info.AddValue ("AdjustmentRules", adjustmentRules);
 645                         info.AddValue ("SupportsDaylightSavingTime", SupportsDaylightSavingTime);
 646                 }
 647
 648                 //FIXME: change this to a generic Dictionary and allow caching for FindSystemTimeZoneById
 649                 private static List<TimeZoneInfo> systemTimeZones;
 650                 public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones ()
 651                 {
 652                         if (systemTimeZones == null) {
 653                                 systemTimeZones = new List<TimeZoneInfo> ();
 654 #if !NET_2_1
 655                                 if (TimeZoneKey != null) {
 656                                         foreach (string id in TimeZoneKey.GetSubKeyNames ()) {
 657                                                 try {
 658                                                         systemTimeZones.Add (FindSystemTimeZoneById (id));
 659                                                 } catch {}
 660                                         }
 661
 662                                         return new ReadOnlyCollection<TimeZoneInfo> (systemTimeZones);
 663                                 }
 664 #endif
 665 #if MONODROID
 666                         foreach (string id in AndroidTimeZones.GetAvailableIds ()) {
 667                                 var tz = AndroidTimeZones.GetTimeZone (id, id);
 668                                 if (tz != null)
 669                                         systemTimeZones.Add (tz);
 670                         }
 671 #elif MONOTOUCH
 672                                 if (systemTimeZones.Count == 0) {
 673                                         foreach (string name in GetMonoTouchNames ()) {
 674                                                 using (Stream stream = GetMonoTouchData (name, false)) {
 675                                                         if (stream == null)
 676                                                                 continue;
 677                                                         systemTimeZones.Add (BuildFromStream (name, stream));
 678                                                 }
 679                                         }
 680                                 }
 681 #elif LIBC
 682                                 string[] continents = new string [] {"Africa", "America", "Antarctica", "Arctic", "Asia", "Atlantic", "Brazil", "Canada", "Chile", "Europe", "Indian", "Mexico", "Mideast", "Pacific", "US"};
 683                                 foreach (string continent in continents) {
 684                                         try {
 685                                                 foreach (string zonepath in Directory.GetFiles (Path.Combine (TimeZoneDirectory, continent))) {
 686                                                         try {
 687                                                                 string id = String.Format ("{0}/{1}", continent, Path.GetFileName (zonepath));
 688                                                                 systemTimeZones.Add (FindSystemTimeZoneById (id));
 689                                                         } catch (ArgumentNullException) {
 690                                                         } catch (TimeZoneNotFoundException) {
 691                                                         } catch (InvalidTimeZoneException) {
 692                                                         } catch (Exception) {
 693                                                                 throw;
 694                                                         }
 695                                                 }
 696                                         } catch {}
 697                                 }
 698 #else
 699                                 throw new NotImplementedException ("This method is not implemented for this platform");
 700 #endif
 701                         }
 702                         return new ReadOnlyCollection<TimeZoneInfo> (systemTimeZones);
 703                 }
 704
 705                 public TimeSpan GetUtcOffset (DateTime dateTime)
 706                 {
 707                         bool isDST;
 708                         return GetUtcOffset (dateTime, out isDST);
 709                 }
 710
 711                 public TimeSpan GetUtcOffset (DateTimeOffset dateTimeOffset)
 712                 {
 713                         throw new NotImplementedException ();
 714                 }
 715
 716                 private TimeSpan GetUtcOffset (DateTime dateTime, out bool isDST)
 717                 {
 718                         isDST = false;
 719
 720                         TimeZoneInfo tz = this;
 721                         if (dateTime.Kind == DateTimeKind.Utc)
 722                                 tz = TimeZoneInfo.Utc;
 723
 724                         if (dateTime.Kind == DateTimeKind.Local)
 725                                 tz = TimeZoneInfo.Local;
 726
 727                         bool isTzDst;
 728                         var tzOffset = GetUtcOffsetHelper (dateTime, tz, out isTzDst);
 729
 730                         if (tz == this) {
 731                                 isDST = isTzDst;
 732                                 return tzOffset;
 733                         }
 734
 735                         DateTime utcDateTime;
 736                         if (!TryAddTicks (dateTime, -tzOffset.Ticks, out utcDateTime, DateTimeKind.Utc))
 737                                 return BaseUtcOffset;
 738
 739                         return GetUtcOffsetHelper (utcDateTime, this, out isDST);
 740                 }
 741
 742                 // This is an helper method used by the method above, do not use this on its own.
 743                 private static TimeSpan GetUtcOffsetHelper (DateTime dateTime, TimeZoneInfo tz, out bool isDST)
 744                 {
 745                         if (dateTime.Kind == DateTimeKind.Local && tz != TimeZoneInfo.Local)
 746                                 throw new Exception ();
 747
 748                         isDST = false;
 749
 750                         if (tz == TimeZoneInfo.Utc)
 751                                 return TimeSpan.Zero;
 752
 753                         TimeSpan offset;
 754                         if (tz.TryGetTransitionOffset(dateTime, out offset, out isDST))
 755                                 return offset;
 756
 757                         if (dateTime.Kind == DateTimeKind.Utc) {
 758                                 var utcRule = tz.GetApplicableRule (dateTime);
 759                                 if (utcRule != null && tz.IsInDST (utcRule, dateTime)) {
 760                                         isDST = true;
 761                                         return tz.BaseUtcOffset + utcRule.DaylightDelta;
 762                                 }
 763
 764                                 return tz.BaseUtcOffset;
 765                         }
 766
 767                         DateTime stdUtcDateTime;
 768                         if (!TryAddTicks (dateTime, -tz.BaseUtcOffset.Ticks, out stdUtcDateTime, DateTimeKind.Utc))
 769                                 return tz.BaseUtcOffset;
 770
 771                         var tzRule = tz.GetApplicableRule (stdUtcDateTime);
 772
 773                         DateTime dstUtcDateTime = DateTime.MinValue;
 774                         if (tzRule != null) {
 775                                 if (!TryAddTicks (stdUtcDateTime, -tzRule.DaylightDelta.Ticks, out dstUtcDateTime, DateTimeKind.Utc))
 776                                         return tz.BaseUtcOffset;
 777                         }
 778
 779                         if (tzRule != null && tz.IsInDST (tzRule, stdUtcDateTime) && tz.IsInDST (tzRule, dstUtcDateTime)) {
 780                                 isDST = true;
 781                                 return tz.BaseUtcOffset + tzRule.DaylightDelta;
 782                         }
 783
 784                         return tz.BaseUtcOffset;
 785                 }
 786
 787                 public bool HasSameRules (TimeZoneInfo other)
 788                 {
 789                         if (other == null)
 790                                 throw new ArgumentNullException ("other");
 791
 792                         if ((this.adjustmentRules == null) != (other.adjustmentRules == null))
 793                                 return false;
 794
 795                         if (this.adjustmentRules == null)
 796                                 return true;
 797
 798                         if (this.BaseUtcOffset != other.BaseUtcOffset)
 799                                 return false;
 800
 801                         if (this.adjustmentRules.Length != other.adjustmentRules.Length)
 802                                 return false;
 803
 804                         for (int i = 0; i < adjustmentRules.Length; i++) {
 805                                 if (! (this.adjustmentRules [i]).Equals (other.adjustmentRules [i]))
 806                                         return false;
 807                         }
 808
 809                         return true;
 810                 }
 811
 812                 public bool IsAmbiguousTime (DateTime dateTime)
 813                 {
 814                         if (dateTime.Kind == DateTimeKind.Local && IsInvalidTime (dateTime))
 815                                 throw new ArgumentException ("Kind is Local and time is Invalid");
 816
 817                         if (this == TimeZoneInfo.Utc)
 818                                 return false;
 819
 820                         if (dateTime.Kind == DateTimeKind.Utc)
 821                                 dateTime = ConvertTimeFromUtc (dateTime);
 822
 823                         if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local)
 824                                 dateTime = ConvertTime (dateTime, TimeZoneInfo.Local, this);
 825
 826                         AdjustmentRule rule = GetApplicableRule (dateTime);
 827                         if (rule != null) {
 828                                 DateTime tpoint = TransitionPoint (rule.DaylightTransitionEnd, dateTime.Year);
 829                                 if (dateTime > tpoint - rule.DaylightDelta  && dateTime <= tpoint)
 830                                         return true;
 831                         }
 832
 833                         return false;
 834                 }
 835
 836                 public bool IsAmbiguousTime (DateTimeOffset dateTimeOffset)
 837                 {
 838                         throw new NotImplementedException ();
 839                 }
 840
 841                 private bool IsInDST (AdjustmentRule rule, DateTime dateTime)
 842                 {
 843                         // Check whether we're in the dateTime year's DST period
 844                         if (IsInDSTForYear (rule, dateTime, dateTime.Year))
 845                                 return true;
 846
 847                         // We might be in the dateTime previous year's DST period
 848                         return IsInDSTForYear (rule, dateTime, dateTime.Year - 1);
 849                 }
 850
 851                 bool IsInDSTForYear (AdjustmentRule rule, DateTime dateTime, int year)
 852                 {
 853                         DateTime DST_start = TransitionPoint (rule.DaylightTransitionStart, year);
 854                         DateTime DST_end = TransitionPoint (rule.DaylightTransitionEnd, year + ((rule.DaylightTransitionStart.Month < rule.DaylightTransitionEnd.Month) ? 0 : 1));
 855                         if (dateTime.Kind == DateTimeKind.Utc) {
 856                                 DST_start -= BaseUtcOffset;
 857                                 DST_end -= (BaseUtcOffset + rule.DaylightDelta);
 858                         }
 859
 860                         return (dateTime >= DST_start && dateTime < DST_end);
 861                 }
 862
 863                 public bool IsDaylightSavingTime (DateTime dateTime)
 864                 {
 865                         if (dateTime.Kind == DateTimeKind.Local && IsInvalidTime (dateTime))
 866                                 throw new ArgumentException ("dateTime is invalid and Kind is Local");
 867
 868                         if (this == TimeZoneInfo.Utc)
 869                                 return false;
 870
 871                         if (!SupportsDaylightSavingTime)
 872                                 return false;
 873
 874                         bool isDst;
 875                         GetUtcOffset (dateTime, out isDst);
 876
 877                         return isDst;
 878                 }
 879
 880                 internal bool IsDaylightSavingTime (DateTime dateTime, TimeZoneInfoOptions flags)
 881                 {
 882                         return IsDaylightSavingTime (dateTime);
 883                 }
 884
 885                 public bool IsDaylightSavingTime (DateTimeOffset dateTimeOffset)
 886                 {
 887                         throw new NotImplementedException ();
 888                 }
 889
 890                 public bool IsInvalidTime (DateTime dateTime)
 891                 {
 892                         if (dateTime.Kind == DateTimeKind.Utc)
 893                                 return false;
 894                         if (dateTime.Kind == DateTimeKind.Local && this != Local)
 895                                 return false;
 896
 897                         AdjustmentRule rule = GetApplicableRule (dateTime);
 898                         if (rule != null) {
 899                                 DateTime tpoint = TransitionPoint (rule.DaylightTransitionStart, dateTime.Year);
 900                                 if (dateTime >= tpoint && dateTime < tpoint + rule.DaylightDelta)
 901                                         return true;
 902                         }
 903
 904                         return false;
 905                 }
 906
 907                 void IDeserializationCallback.OnDeserialization (object sender)
 908                 {
 909                         try {
 910                                         TimeZoneInfo.Validate (id, baseUtcOffset, adjustmentRules);
 911                                 } catch (ArgumentException ex) {
 912                                         throw new SerializationException ("invalid serialization data", ex);
 913                                 }
 914                 }
 915
 916                 private static void Validate (string id, TimeSpan baseUtcOffset, AdjustmentRule [] adjustmentRules)
 917                 {
 918                         if (id == null)
 919                                 throw new ArgumentNullException ("id");
 920
 921                         if (id == String.Empty)
 922                                 throw new ArgumentException ("id parameter is an empty string");
 923
 924                         if (baseUtcOffset.Ticks % TimeSpan.TicksPerMinute != 0)
 925                                 throw new ArgumentException ("baseUtcOffset parameter does not represent a whole number of minutes");
 926
 927                         if (baseUtcOffset > new TimeSpan (14, 0, 0) || baseUtcOffset < new TimeSpan (-14, 0, 0))
 928                                 throw new ArgumentOutOfRangeException ("baseUtcOffset parameter is greater than 14 hours or less than -14 hours");
 929
 930 #if STRICT
 931                         if (id.Length > 32)
 932                                 throw new ArgumentException ("id parameter shouldn't be longer than 32 characters");
 933 #endif
 934
 935                         if (adjustmentRules != null && adjustmentRules.Length != 0) {
 936                                 AdjustmentRule prev = null;
 937                                 foreach (AdjustmentRule current in adjustmentRules) {
 938                                         if (current == null)
 939                                                 throw new InvalidTimeZoneException ("one or more elements in adjustmentRules are null");
 940
 941                                         if ((baseUtcOffset + current.DaylightDelta < new TimeSpan (-14, 0, 0)) ||
 942                                                         (baseUtcOffset + current.DaylightDelta > new TimeSpan (14, 0, 0)))
 943                                                 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;");
 944
 945                                         if (prev != null && prev.DateStart > current.DateStart)
 946                                                 throw new InvalidTimeZoneException ("adjustment rules specified in adjustmentRules parameter are not in chronological order");
 947
 948                                         if (prev != null && prev.DateEnd > current.DateStart)
 949                                                 throw new InvalidTimeZoneException ("some adjustment rules in the adjustmentRules parameter overlap");
 950
 951                                         if (prev != null && prev.DateEnd == current.DateStart)
 952                                                 throw new InvalidTimeZoneException ("a date can have multiple adjustment rules applied to it");
 953
 954                                         prev = current;
 955                                 }
 956                         }
 957                 }
 958
 959                 public override string ToString ()
 960                 {
 961                         return DisplayName;
 962                 }
 963
 964                 private TimeZoneInfo (SerializationInfo info, StreamingContext context)
 965                 {
 966                         if (info == null)
 967                                 throw new ArgumentNullException ("info");
 968                         id = (string) info.GetValue ("Id", typeof (string));
 969                         displayName = (string) info.GetValue ("DisplayName", typeof (string));
 970                         standardDisplayName = (string) info.GetValue ("StandardName", typeof (string));
 971                         daylightDisplayName = (string) info.GetValue ("DaylightName", typeof (string));
 972                         baseUtcOffset = (TimeSpan) info.GetValue ("BaseUtcOffset", typeof (TimeSpan));
 973                         adjustmentRules = (TimeZoneInfo.AdjustmentRule []) info.GetValue ("AdjustmentRules", typeof (TimeZoneInfo.AdjustmentRule []));
 974                         supportsDaylightSavingTime = (bool) info.GetValue ("SupportsDaylightSavingTime", typeof (bool));
 975                 }
 976
 977                 private TimeZoneInfo (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules, bool disableDaylightSavingTime)
 978                 {
 979                         if (id == null)
 980                                 throw new ArgumentNullException ("id");
 981
 982                         if (id == String.Empty)
 983                                 throw new ArgumentException ("id parameter is an empty string");
 984
 985                         if (baseUtcOffset.Ticks % TimeSpan.TicksPerMinute != 0)
 986                                 throw new ArgumentException ("baseUtcOffset parameter does not represent a whole number of minutes");
 987
 988                         if (baseUtcOffset > new TimeSpan (14, 0, 0) || baseUtcOffset < new TimeSpan (-14, 0, 0))
 989                                 throw new ArgumentOutOfRangeException ("baseUtcOffset parameter is greater than 14 hours or less than -14 hours");
 990
 991 #if STRICT
 992                         if (id.Length > 32)
 993                                 throw new ArgumentException ("id parameter shouldn't be longer than 32 characters");
 994 #endif
 995
 996                         bool supportsDaylightSavingTime = !disableDaylightSavingTime;
 997
 998                         if (adjustmentRules != null && adjustmentRules.Length != 0) {
 999                                 AdjustmentRule prev = null;
1000                                 foreach (AdjustmentRule current in adjustmentRules) {
1001                                         if (current == null)
1002                                                 throw new InvalidTimeZoneException ("one or more elements in adjustmentRules are null");
1003
1004                                         if ((baseUtcOffset + current.DaylightDelta < new TimeSpan (-14, 0, 0)) ||
1005                                                         (baseUtcOffset + current.DaylightDelta > new TimeSpan (14, 0, 0)))
1006                                                 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;");
1007
1008                                         if (prev != null && prev.DateStart > current.DateStart)
1009                                                 throw new InvalidTimeZoneException ("adjustment rules specified in adjustmentRules parameter are not in chronological order");
1010
1011                                         if (prev != null && prev.DateEnd > current.DateStart)
1012                                                 throw new InvalidTimeZoneException ("some adjustment rules in the adjustmentRules parameter overlap");
1013
1014                                         if (prev != null && prev.DateEnd == current.DateStart)
1015                                                 throw new InvalidTimeZoneException ("a date can have multiple adjustment rules applied to it");
1016
1017                                         prev = current;
1018                                 }
1019                         } else {
1020                                 supportsDaylightSavingTime = false;
1021                         }
1022
1023                         this.id = id;
1024                         this.baseUtcOffset = baseUtcOffset;
1025                         this.displayName = displayName ?? id;
1026                         this.standardDisplayName = standardDisplayName ?? id;
1027                         this.daylightDisplayName = daylightDisplayName;
1028                         this.supportsDaylightSavingTime = supportsDaylightSavingTime;
1029                         this.adjustmentRules = adjustmentRules;
1030                 }
1031
1032                 private AdjustmentRule GetApplicableRule (DateTime dateTime)
1033                 {
1034                         //Applicable rules are in standard time
1035                         DateTime date = dateTime;
1036
1037                         if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local) {
1038                                 if (!TryAddTicks (date.ToUniversalTime (), BaseUtcOffset.Ticks, out date))
1039                                         return null;
1040                         } else if (dateTime.Kind == DateTimeKind.Utc && this != TimeZoneInfo.Utc) {
1041                                 if (!TryAddTicks (date, BaseUtcOffset.Ticks, out date))
1042                                         return null;
1043                         }
1044
1045                         // get the date component of the datetime
1046                         date = date.Date;
1047
1048                         if (adjustmentRules != null) {
1049                                 foreach (AdjustmentRule rule in adjustmentRules) {
1050                                         if (rule.DateStart > date)
1051                                                 return null;
1052                                         if (rule.DateEnd < date)
1053                                                 continue;
1054                                         return rule;
1055                                 }
1056                         }
1057                         return null;
1058                 }
1059
1060                 private bool TryGetTransitionOffset (DateTime dateTime, out TimeSpan offset,out bool isDst)
1061                 {
1062                         offset = BaseUtcOffset;
1063                         isDst = false;
1064
1065                         if (transitions == null)
1066                                 return false;
1067
1068                         //Transitions are in UTC
1069                         DateTime date = dateTime;
1070
1071                         if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local) {
1072                                 if (!TryAddTicks (date.ToUniversalTime (), BaseUtcOffset.Ticks, out date, DateTimeKind.Utc))
1073                                         return false;
1074                         }
1075
1076                         if (dateTime.Kind != DateTimeKind.Utc) {
1077                                 if (!TryAddTicks (date, -BaseUtcOffset.Ticks, out date, DateTimeKind.Utc))
1078                                         return false;
1079                         }
1080
1081                         for (var i =  transitions.Count - 1; i >= 0; i--) {
1082                                 var pair = transitions [i];
1083                                 DateTime ttime = pair.Key;
1084                                 TimeType ttype = pair.Value;
1085
1086                                 if (ttime > date)
1087                                         continue;
1088
1089                                 offset =  new TimeSpan (0, 0, ttype.Offset);
1090                                 isDst = ttype.IsDst;
1091
1092                                 return true;
1093                         }
1094
1095                         return false;
1096                 }
1097
1098                 private static DateTime TransitionPoint (TransitionTime transition, int year)
1099                 {
1100                         if (transition.IsFixedDateRule)
1101                                 return new DateTime (year, transition.Month, transition.Day) + transition.TimeOfDay.TimeOfDay;
1102
1103                         DayOfWeek first = (new DateTime (year, transition.Month, 1)).DayOfWeek;
1104                         int day = 1 + (transition.Week - 1) * 7 + (transition.DayOfWeek - first + 7) % 7;
1105                         if (day >  DateTime.DaysInMonth (year, transition.Month))
1106                                 day -= 7;
1107                         if (day < 1)
1108                                 day += 7;
1109                         return new DateTime (year, transition.Month, day) + transition.TimeOfDay.TimeOfDay;
1110                 }
1111
1112                 static List<AdjustmentRule> ValidateRules (List<AdjustmentRule> adjustmentRules)
1113                 {
1114                         AdjustmentRule prev = null;
1115                         foreach (AdjustmentRule current in adjustmentRules.ToArray ()) {
1116                                 if (prev != null && prev.DateEnd > current.DateStart) {
1117                                         adjustmentRules.Remove (current);
1118                                 }
1119                                 prev = current;
1120                         }
1121                         return adjustmentRules;
1122                 }
1123
1124 #if LIBC || MONODROID
1125                 private static bool ValidTZFile (byte [] buffer, int length)
1126                 {
1127                         StringBuilder magic = new StringBuilder ();
1128
1129                         for (int i = 0; i < 4; i++)
1130                                 magic.Append ((char)buffer [i]);
1131
1132                         if (magic.ToString () != "TZif")
1133                                 return false;
1134
1135                         if (length >= BUFFER_SIZE)
1136                                 return false;
1137
1138                         return true;
1139                 }
1140
1141                 static int SwapInt32 (int i)
1142                 {
1143                         return (((i >> 24) & 0xff)
1144                                 | ((i >> 8) & 0xff00)
1145                                 | ((i << 8) & 0xff0000)
1146                                 | ((i << 24)));
1147                 }
1148
1149                 static int ReadBigEndianInt32 (byte [] buffer, int start)
1150                 {
1151                         int i = BitConverter.ToInt32 (buffer, start);
1152                         if (!BitConverter.IsLittleEndian)
1153                                 return i;
1154
1155                         return SwapInt32 (i);
1156                 }
1157
1158                 private static TimeZoneInfo ParseTZBuffer (string id, byte [] buffer, int length)
1159                 {
1160                         //Reading the header. 4 bytes for magic, 16 are reserved
1161                         int ttisgmtcnt = ReadBigEndianInt32 (buffer, 20);
1162                         int ttisstdcnt = ReadBigEndianInt32 (buffer, 24);
1163                         int leapcnt = ReadBigEndianInt32 (buffer, 28);
1164                         int timecnt = ReadBigEndianInt32 (buffer, 32);
1165                         int typecnt = ReadBigEndianInt32 (buffer, 36);
1166                         int charcnt = ReadBigEndianInt32 (buffer, 40);
1167
1168                         if (length < 44 + timecnt * 5 + typecnt * 6 + charcnt + leapcnt * 8 + ttisstdcnt + ttisgmtcnt)
1169                                 throw new InvalidTimeZoneException ();
1170
1171                         Dictionary<int, string> abbreviations = ParseAbbreviations (buffer, 44 + 4 * timecnt + timecnt + 6 * typecnt, charcnt);
1172                         Dictionary<int, TimeType> time_types = ParseTimesTypes (buffer, 44 + 4 * timecnt + timecnt, typecnt, abbreviations);
1173                         List<KeyValuePair<DateTime, TimeType>> transitions = ParseTransitions (buffer, 44, timecnt, time_types);
1174
1175                         if (time_types.Count == 0)
1176                                 throw new InvalidTimeZoneException ();
1177
1178                         if (time_types.Count == 1 && ((TimeType)time_types[0]).IsDst)
1179                                 throw new InvalidTimeZoneException ();
1180
1181                         TimeSpan baseUtcOffset = new TimeSpan (0);
1182                         TimeSpan dstDelta = new TimeSpan (0);
1183                         string standardDisplayName = null;
1184                         string daylightDisplayName = null;
1185                         bool dst_observed = false;
1186                         DateTime dst_start = DateTime.MinValue;
1187                         List<AdjustmentRule> adjustmentRules = new List<AdjustmentRule> ();
1188                         bool storeTransition = false;
1189
1190                         for (int i = 0; i < transitions.Count; i++) {
1191                                 var pair = transitions [i];
1192                                 DateTime ttime = pair.Key;
1193                                 TimeType ttype = pair.Value;
1194                                 if (!ttype.IsDst) {
1195                                         if (standardDisplayName != ttype.Name)
1196                                                 standardDisplayName = ttype.Name;
1197                                         if (baseUtcOffset.TotalSeconds != ttype.Offset) {
1198                                                 baseUtcOffset = new TimeSpan (0, 0, ttype.Offset);
1199                                                 if (adjustmentRules.Count > 0) // We ignore AdjustmentRules but store transitions.
1200                                                         storeTransition = true;
1201                                                 adjustmentRules = new List<AdjustmentRule> ();
1202                                                 dst_observed = false;
1203                                         }
1204                                         if (dst_observed) {
1205                                                 //FIXME: check additional fields for this:
1206                                                 //most of the transitions are expressed in GMT
1207                                                 dst_start += baseUtcOffset;
1208                                                 DateTime dst_end = ttime + baseUtcOffset + dstDelta;
1209
1210                                                 //some weird timezone (America/Phoenix) have end dates on Jan 1st
1211                                                 if (dst_end.Date == new DateTime (dst_end.Year, 1, 1) && dst_end.Year > dst_start.Year)
1212                                                         dst_end -= new TimeSpan (24, 0, 0);
1213
1214                                                 /*
1215                                                  * AdjustmentRule specifies a DST period that starts and ends within a year.
1216                                                  * When we have a DST period longer than a year, the generated AdjustmentRule may not be usable.
1217                                                  * Thus we fallback to the transitions.
1218                                                  */
1219                                                 if (dst_start.AddYears (1) < dst_end)
1220                                                         storeTransition = true;
1221
1222                                                 DateTime dateStart, dateEnd;
1223                                                 if (dst_start.Month < 7)
1224                                                         dateStart = new DateTime (dst_start.Year, 1, 1);
1225                                                 else
1226                                                         dateStart = new DateTime (dst_start.Year, 7, 1);
1227
1228                                                 if (dst_end.Month >= 7)
1229                                                         dateEnd = new DateTime (dst_end.Year, 12, 31);
1230                                                 else
1231                                                         dateEnd = new DateTime (dst_end.Year, 6, 30);
1232
1233
1234                                                 TransitionTime transition_start = TransitionTime.CreateFixedDateRule (new DateTime (1, 1, 1) + dst_start.TimeOfDay, dst_start.Month, dst_start.Day);
1235                                                 TransitionTime transition_end = TransitionTime.CreateFixedDateRule (new DateTime (1, 1, 1) + dst_end.TimeOfDay, dst_end.Month, dst_end.Day);
1236                                                 if  (transition_start != transition_end) //y, that happened in Argentina in 1943-1946
1237                                                         adjustmentRules.Add (AdjustmentRule.CreateAdjustmentRule (dateStart, dateEnd, dstDelta, transition_start, transition_end));
1238                                         }
1239                                         dst_observed = false;
1240                                 } else {
1241                                         if (daylightDisplayName != ttype.Name)
1242                                                 daylightDisplayName = ttype.Name;
1243                                         if (dstDelta.TotalSeconds != ttype.Offset - baseUtcOffset.TotalSeconds)
1244                                                 dstDelta = new TimeSpan(0, 0, ttype.Offset) - baseUtcOffset;
1245
1246                                         dst_start = ttime;
1247                                         dst_observed = true;
1248                                 }
1249                         }
1250
1251                         TimeZoneInfo tz;
1252                         if (adjustmentRules.Count == 0 && !storeTransition) {
1253                                 TimeType t = (TimeType)time_types [0];
1254                                 if (standardDisplayName == null) {
1255                                         standardDisplayName = t.Name;
1256                                         baseUtcOffset = new TimeSpan (0, 0, t.Offset);
1257                                 }
1258                                 tz = CreateCustomTimeZone (id, baseUtcOffset, id, standardDisplayName);
1259                         } else {
1260                                 tz = CreateCustomTimeZone (id, baseUtcOffset, id, standardDisplayName, daylightDisplayName, ValidateRules (adjustmentRules).ToArray ());
1261                         }
1262
1263                         if (storeTransition)
1264                                 tz.transitions = transitions;
1265
1266                         return tz;
1267                 }
1268
1269                 static Dictionary<int, string> ParseAbbreviations (byte [] buffer, int index, int count)
1270                 {
1271                         var abbrevs = new Dictionary<int, string> ();
1272                         int abbrev_index = 0;
1273                         var sb = new StringBuilder ();
1274                         for (int i = 0; i < count; i++) {
1275                                 char c = (char) buffer [index + i];
1276                                 if (c != '\0')
1277                                         sb.Append (c);
1278                                 else {
1279                                         abbrevs.Add (abbrev_index, sb.ToString ());
1280                                         //Adding all the substrings too, as it seems to be used, at least for Africa/Windhoek
1281                                         for (int j = 1; j < sb.Length; j++)
1282                                                 abbrevs.Add (abbrev_index + j, sb.ToString (j, sb.Length - j));
1283                                         abbrev_index = i + 1;
1284                                         sb = new StringBuilder ();
1285                                 }
1286                         }
1287                         return abbrevs;
1288                 }
1289
1290                 static Dictionary<int, TimeType> ParseTimesTypes (byte [] buffer, int index, int count, Dictionary<int, string> abbreviations)
1291                 {
1292                         var types = new Dictionary<int, TimeType> (count);
1293                         for (int i = 0; i < count; i++) {
1294                                 int offset = ReadBigEndianInt32 (buffer, index + 6 * i);
1295                                 byte is_dst = buffer [index + 6 * i + 4];
1296                                 byte abbrev = buffer [index + 6 * i + 5];
1297                                 types.Add (i, new TimeType (offset, (is_dst != 0), abbreviations [(int)abbrev]));
1298                         }
1299                         return types;
1300                 }
1301
1302                 static List<KeyValuePair<DateTime, TimeType>> ParseTransitions (byte [] buffer, int index, int count, Dictionary<int, TimeType> time_types)
1303                 {
1304                         var list = new List<KeyValuePair<DateTime, TimeType>> (count);
1305                         for (int i = 0; i < count; i++) {
1306                                 int unixtime = ReadBigEndianInt32 (buffer, index + 4 * i);
1307                                 DateTime ttime = DateTimeFromUnixTime (unixtime);
1308                                 byte ttype = buffer [index + 4 * count + i];
1309                                 list.Add (new KeyValuePair<DateTime, TimeType> (ttime, time_types [(int)ttype]));
1310                         }
1311                         return list;
1312                 }
1313
1314                 static DateTime DateTimeFromUnixTime (long unix_time)
1315                 {
1316                         DateTime date_time = new DateTime (1970, 1, 1);
1317                         return date_time.AddSeconds (unix_time);
1318                 }
1319
1320 #region reference sources
1321                 // Shortcut for TimeZoneInfo.Local.GetUtcOffset
1322                 internal static TimeSpan GetLocalUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
1323                 {
1324                         bool dst;
1325                         return Local.GetUtcOffset (dateTime, out dst);
1326                 }
1327
1328                 internal TimeSpan GetUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
1329                 {
1330                         bool dst;
1331                         return GetUtcOffset (dateTime, out dst);
1332                 }
1333
1334                 static internal TimeSpan GetUtcOffsetFromUtc (DateTime time, TimeZoneInfo zone, out Boolean isDaylightSavings, out Boolean isAmbiguousLocalDst)
1335                 {
1336                         isDaylightSavings = false;
1337                         isAmbiguousLocalDst = false;
1338                         TimeSpan baseOffset = zone.BaseUtcOffset;
1339
1340                         if (zone.IsAmbiguousTime (time)) {
1341                                 isAmbiguousLocalDst = true;
1342                                 return baseOffset;
1343                         }
1344
1345                         return zone.GetUtcOffset (time, out isDaylightSavings);
1346                 }
1347 #endregion
1348         }
1349
1350         struct TimeType {
1351                 public readonly int Offset;
1352                 public readonly bool IsDst;
1353                 public string Name;
1354
1355                 public TimeType (int offset, bool is_dst, string abbrev)
1356                 {
1357                         this.Offset = offset;
1358                         this.IsDst = is_dst;
1359                         this.Name = abbrev;
1360                 }
1361
1362                 public override string ToString ()
1363                 {
1364                         return "offset: " + Offset + "s, is_dst: " + IsDst + ", zone name: " + Name;
1365                 }
1366 #else
1367         }
1368 #endif
1369         }
1370 }