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         partial class TimeZoneInfo
  49         {
  50                 TimeSpan baseUtcOffset;
  51                 public TimeSpan BaseUtcOffset {
  52                         get { return baseUtcOffset; }
  53                 }
  54
  55                 string daylightDisplayName;
  56                 public string DaylightName {
  57                         get {
  58                                 return supportsDaylightSavingTime
  59                                         ? daylightDisplayName
  60                                         : string.Empty;
  61                         }
  62                 }
  63
  64                 string displayName;
  65                 public string DisplayName {
  66                         get { return displayName; }
  67                 }
  68
  69                 string id;
  70                 public string Id {
  71                         get { return id; }
  72                 }
  73
  74                 static TimeZoneInfo local;
  75                 public static TimeZoneInfo Local {
  76                         get {
  77                                 var l = local;
  78                                 if (l == null) {
  79                                         l = CreateLocal ();
  80                                         if (l == null)
  81                                                 throw new TimeZoneNotFoundException ();
  82
  83                                         if (Interlocked.CompareExchange (ref local, l, null) != null)
  84                                                 l = local;
  85                                 }
  86
  87                                 return l;
  88                         }
  89                 }
  90
  91                 /*
  92                         TimeZone transitions are stored when there is a change on the base offset.
  93                 */
  94                 private List<KeyValuePair<DateTime, TimeType>> transitions;
  95
  96                 static TimeZoneInfo CreateLocal ()
  97                 {
  98 #if MONODROID
  99                         return AndroidTimeZones.Local;
 100 #elif MONOTOUCH
 101                         using (Stream stream = GetMonoTouchData (null)) {
 102                                 return BuildFromStream ("Local", stream);
 103                         }
 104 #else
 105 #if !NET_2_1
 106                         if (IsWindows && LocalZoneKey != null) {
 107                                 string name = (string)LocalZoneKey.GetValue ("TimeZoneKeyName");
 108                                 if (name == null)
 109                                         name = (string)LocalZoneKey.GetValue ("StandardName"); // windows xp
 110                                 name = TrimSpecial (name);
 111                                 if (name != null)
 112                                         return TimeZoneInfo.FindSystemTimeZoneById (name);
 113                         }
 114 #endif
 115
 116                         var tz = Environment.GetEnvironmentVariable ("TZ");
 117                         if (tz != null) {
 118                                 if (tz == String.Empty)
 119                                         return Utc;
 120                                 try {
 121                                         return FindSystemTimeZoneByFileName (tz, Path.Combine (TimeZoneDirectory, tz));
 122                                 } catch {
 123                                         return Utc;
 124                                 }
 125                         }
 126
 127                         try {
 128                                 return FindSystemTimeZoneByFileName ("Local", "/etc/localtime");
 129                         } catch {
 130                                 try {
 131                                         return FindSystemTimeZoneByFileName ("Local", Path.Combine (TimeZoneDirectory, "localtime"));
 132                                 } catch {
 133                                         return null;
 134                                 }
 135                         }
 136 #endif
 137                 }
 138
 139                 string standardDisplayName;
 140                 public string StandardName {
 141                         get { return standardDisplayName; }
 142                 }
 143
 144                 bool supportsDaylightSavingTime;
 145                 public bool SupportsDaylightSavingTime {
 146                         get  { return supportsDaylightSavingTime; }
 147                 }
 148
 149                 static TimeZoneInfo utc;
 150                 public static TimeZoneInfo Utc {
 151                         get {
 152                                 if (utc == null)
 153                                         utc = CreateCustomTimeZone ("UTC", new TimeSpan (0), "UTC", "UTC");
 154                                 return utc;
 155                         }
 156                 }
 157 #if LIBC
 158                 static string timeZoneDirectory;
 159                 static string TimeZoneDirectory {
 160                         get {
 161                                 if (timeZoneDirectory == null)
 162                                         timeZoneDirectory = "/usr/share/zoneinfo";
 163                                 return timeZoneDirectory;
 164                         }
 165                         set {
 166                                 ClearCachedData ();
 167                                 timeZoneDirectory = value;
 168                         }
 169                 }
 170 #endif
 171                 private AdjustmentRule [] adjustmentRules;
 172
 173 #if !NET_2_1
 174                 /// <summary>
 175                 /// Determine whether windows of not (taken Stephane Delcroix's code)
 176                 /// </summary>
 177                 private static bool IsWindows
 178                 {
 179                         get {
 180                                 int platform = (int) Environment.OSVersion.Platform;
 181                                 return ((platform != 4) && (platform != 6) && (platform != 128));
 182                         }
 183                 }
 184
 185                 /// <summary>
 186                 /// Needed to trim misc garbage in MS registry keys
 187                 /// </summary>
 188                 private static string TrimSpecial (string str)
 189                 {
 190                         if (str == null)
 191                                 return str;
 192                         var Istart = 0;
 193                         while (Istart < str.Length && !char.IsLetterOrDigit(str[Istart])) Istart++;
 194                         var Iend = str.Length - 1;
 195                         while (Iend > Istart && !char.IsLetterOrDigit(str[Iend])) Iend--;
 196
 197                         return str.Substring (Istart, Iend-Istart+1);
 198                 }
 199
 200                 static RegistryKey timeZoneKey;
 201                 static RegistryKey TimeZoneKey {
 202                         get {
 203                                 if (timeZoneKey != null)
 204                                         return timeZoneKey;
 205                                 if (!IsWindows)
 206                                         return null;
 207
 208                                 return timeZoneKey = Registry.LocalMachine.OpenSubKey (
 209                                         "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones",
 210                                         false);
 211                         }
 212                 }
 213
 214                 static RegistryKey localZoneKey;
 215                 static RegistryKey LocalZoneKey {
 216                         get {
 217                                 if (localZoneKey != null)
 218                                         return localZoneKey;
 219
 220                                 if (!IsWindows)
 221                                         return null;
 222
 223                                 return localZoneKey = Registry.LocalMachine.OpenSubKey (
 224                                         "SYSTEM\\CurrentControlSet\\Control\\TimeZoneInformation", false);
 225                         }
 226                 }
 227 #endif
 228
 229                 private static bool TryAddTicks (DateTime date, long ticks, out DateTime result, DateTimeKind kind = DateTimeKind.Unspecified)
 230                 {
 231                         var resultTicks = date.Ticks + ticks;
 232                         if (resultTicks < DateTime.MinValue.Ticks || resultTicks > DateTime.MaxValue.Ticks) {
 233                                 result =  default (DateTime);
 234                                 return false;
 235                         }
 236
 237                         result = new DateTime (resultTicks, kind);
 238                         return true;
 239                 }
 240
 241                 public static void ClearCachedData ()
 242                 {
 243                         local = null;
 244                         utc = null;
 245                         systemTimeZones = null;
 246                 }
 247
 248                 public static DateTime ConvertTime (DateTime dateTime, TimeZoneInfo destinationTimeZone)
 249                 {
 250                         return ConvertTime (dateTime, dateTime.Kind == DateTimeKind.Utc ? TimeZoneInfo.Utc : TimeZoneInfo.Local, destinationTimeZone);
 251                 }
 252
 253                 public static DateTime ConvertTime (DateTime dateTime, TimeZoneInfo sourceTimeZone, TimeZoneInfo destinationTimeZone)
 254                 {
 255                         if (sourceTimeZone == null)
 256                                 throw new ArgumentNullException ("sourceTimeZone");
 257
 258                         if (destinationTimeZone == null)
 259                                 throw new ArgumentNullException ("destinationTimeZone");
 260
 261                         if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone != TimeZoneInfo.Local)
 262                                 throw new ArgumentException ("Kind property of dateTime is Local but the sourceTimeZone does not equal TimeZoneInfo.Local");
 263
 264                         if (dateTime.Kind == DateTimeKind.Utc && sourceTimeZone != TimeZoneInfo.Utc)
 265                                 throw new ArgumentException ("Kind property of dateTime is Utc but the sourceTimeZone does not equal TimeZoneInfo.Utc");
 266
 267                         if (sourceTimeZone.IsInvalidTime (dateTime))
 268                                 throw new ArgumentException ("dateTime parameter is an invalid time");
 269
 270                         if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone == TimeZoneInfo.Local && destinationTimeZone == TimeZoneInfo.Local)
 271                                 return dateTime;
 272
 273                         DateTime utc = ConvertTimeToUtc (dateTime, sourceTimeZone);
 274
 275                         if (destinationTimeZone != TimeZoneInfo.Utc) {
 276                                 utc = ConvertTimeFromUtc (utc, destinationTimeZone);
 277                                 if (dateTime.Kind == DateTimeKind.Unspecified)
 278                                         return DateTime.SpecifyKind (utc, DateTimeKind.Unspecified);
 279                         }
 280
 281                         return utc;
 282                 }
 283
 284                 public static DateTimeOffset ConvertTime(DateTimeOffset dateTimeOffset, TimeZoneInfo destinationTimeZone)
 285                 {
 286                         if (destinationTimeZone == null)
 287                                 throw new ArgumentNullException("destinationTimeZone");
 288
 289                         var utcDateTime = dateTimeOffset.UtcDateTime;
 290
 291                         bool isDst;
 292                         var utcOffset =  destinationTimeZone.GetUtcOffset(utcDateTime, out isDst);
 293
 294                         return new DateTimeOffset(DateTime.SpecifyKind(utcDateTime, DateTimeKind.Unspecified) + utcOffset, utcOffset);
 295                 }
 296
 297                 public static DateTime ConvertTimeBySystemTimeZoneId (DateTime dateTime, string destinationTimeZoneId)
 298                 {
 299                         return ConvertTime (dateTime, FindSystemTimeZoneById (destinationTimeZoneId));
 300                 }
 301
 302                 public static DateTime ConvertTimeBySystemTimeZoneId (DateTime dateTime, string sourceTimeZoneId, string destinationTimeZoneId)
 303                 {
 304                         return ConvertTime (dateTime, FindSystemTimeZoneById (sourceTimeZoneId), FindSystemTimeZoneById (destinationTimeZoneId));
 305                 }
 306
 307                 public static DateTimeOffset ConvertTimeBySystemTimeZoneId (DateTimeOffset dateTimeOffset, string destinationTimeZoneId)
 308                 {
 309                         return ConvertTime (dateTimeOffset, FindSystemTimeZoneById (destinationTimeZoneId));
 310                 }
 311
 312                 private DateTime ConvertTimeFromUtc (DateTime dateTime)
 313                 {
 314                         if (dateTime.Kind == DateTimeKind.Local)
 315                                 throw new ArgumentException ("Kind property of dateTime is Local");
 316
 317                         if (this == TimeZoneInfo.Utc)
 318                                 return DateTime.SpecifyKind (dateTime, DateTimeKind.Utc);
 319
 320                         var utcOffset = GetUtcOffset (dateTime);
 321
 322                         var kind = (this == TimeZoneInfo.Local)? DateTimeKind.Local : DateTimeKind.Unspecified;
 323
 324                         DateTime result;
 325                         if (!TryAddTicks (dateTime, utcOffset.Ticks, out result, kind))
 326                                 return DateTime.SpecifyKind (DateTime.MaxValue, kind);
 327
 328                         return result;
 329                 }
 330
 331                 public static DateTime ConvertTimeFromUtc (DateTime dateTime, TimeZoneInfo destinationTimeZone)
 332                 {
 333                         if (destinationTimeZone == null)
 334                                 throw new ArgumentNullException ("destinationTimeZone");
 335
 336                         return destinationTimeZone.ConvertTimeFromUtc (dateTime);
 337                 }
 338
 339                 public static DateTime ConvertTimeToUtc (DateTime dateTime)
 340                 {
 341                         if (dateTime.Kind == DateTimeKind.Utc)
 342                                 return dateTime;
 343
 344                         return ConvertTimeToUtc (dateTime, TimeZoneInfo.Local);
 345                 }
 346
 347                 static internal DateTime ConvertTimeToUtc(DateTime dateTime, TimeZoneInfoOptions flags)
 348                 {
 349                         return ConvertTimeToUtc (dateTime, TimeZoneInfo.Local, flags);
 350                 }
 351
 352                 public static DateTime ConvertTimeToUtc (DateTime dateTime, TimeZoneInfo sourceTimeZone)
 353                 {
 354                         return ConvertTimeToUtc (dateTime, sourceTimeZone, TimeZoneInfoOptions.None);
 355                 }
 356
 357                 static DateTime ConvertTimeToUtc (DateTime dateTime, TimeZoneInfo sourceTimeZone, TimeZoneInfoOptions flags)
 358                 {
 359                         if ((flags & TimeZoneInfoOptions.NoThrowOnInvalidTime) == 0) {
 360                                 if (sourceTimeZone == null)
 361                                         throw new ArgumentNullException ("sourceTimeZone");
 362
 363                                 if (dateTime.Kind == DateTimeKind.Utc && sourceTimeZone != TimeZoneInfo.Utc)
 364                                         throw new ArgumentException ("Kind property of dateTime is Utc but the sourceTimeZone does not equal TimeZoneInfo.Utc");
 365
 366                                 if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone != TimeZoneInfo.Local)
 367                                         throw new ArgumentException ("Kind property of dateTime is Local but the sourceTimeZone does not equal TimeZoneInfo.Local");
 368
 369                                 if (sourceTimeZone.IsInvalidTime (dateTime))
 370                                         throw new ArgumentException ("dateTime parameter is an invalid time");
 371                         }
 372
 373                         if (dateTime.Kind == DateTimeKind.Utc)
 374                                 return dateTime;
 375
 376                         bool isDst;
 377                         var utcOffset = sourceTimeZone.GetUtcOffset (dateTime, out isDst);
 378
 379                         DateTime utcDateTime;
 380                         if (!TryAddTicks (dateTime, -utcOffset.Ticks, out utcDateTime, DateTimeKind.Utc))
 381                                 return DateTime.SpecifyKind (DateTime.MinValue, DateTimeKind.Utc);
 382
 383                         return utcDateTime;
 384                 }
 385
 386                 static internal TimeSpan GetDateTimeNowUtcOffsetFromUtc(DateTime time, out Boolean isAmbiguousLocalDst)
 387                 {
 388                         bool isDaylightSavings;
 389                         return GetUtcOffsetFromUtc(time, TimeZoneInfo.Local, out isDaylightSavings, out isAmbiguousLocalDst);
 390                 }
 391
 392                 public static TimeZoneInfo CreateCustomTimeZone (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName)
 393                 {
 394                         return CreateCustomTimeZone (id, baseUtcOffset, displayName, standardDisplayName, null, null, true);
 395                 }
 396
 397                 public static TimeZoneInfo CreateCustomTimeZone (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules)
 398                 {
 399                         return CreateCustomTimeZone (id, baseUtcOffset, displayName, standardDisplayName, daylightDisplayName, adjustmentRules, false);
 400                 }
 401
 402                 public static TimeZoneInfo CreateCustomTimeZone ( string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules, bool disableDaylightSavingTime)
 403                 {
 404                         return new TimeZoneInfo (id, baseUtcOffset, displayName, standardDisplayName, daylightDisplayName, adjustmentRules, disableDaylightSavingTime);
 405                 }
 406
 407                 public override bool Equals (object obj)
 408                 {
 409                         return Equals (obj as TimeZoneInfo);
 410                 }
 411
 412                 public bool Equals (TimeZoneInfo other)
 413                 {
 414                         if (other == null)
 415                                 return false;
 416
 417                         return other.Id == this.Id && HasSameRules (other);
 418                 }
 419
 420                 public static TimeZoneInfo FindSystemTimeZoneById (string id)
 421                 {
 422                         //FIXME: this method should check for cached values in systemTimeZones
 423                         if (id == null)
 424                                 throw new ArgumentNullException ("id");
 425 #if !NET_2_1
 426                         if (TimeZoneKey != null)
 427                         {
 428                                 if (id == "Coordinated Universal Time")
 429                                         id = "UTC"; //windows xp exception for "StandardName" property
 430                                 RegistryKey key = TimeZoneKey.OpenSubKey (id, false);
 431                                 if (key == null)
 432                                         throw new TimeZoneNotFoundException ();
 433                                 return FromRegistryKey(id, key);
 434                         }
 435 #endif
 436                         // Local requires special logic that already exists in the Local property (bug #326)
 437                         if (id == "Local")
 438                                 return Local;
 439 #if MONOTOUCH
 440                         using (Stream stream = GetMonoTouchData (id)) {
 441                                 return BuildFromStream (id, stream);
 442                         }
 443 #elif MONODROID
 444                         var timeZoneInfo = AndroidTimeZones.GetTimeZone (id, id);
 445                         if (timeZoneInfo == null)
 446                                 throw new TimeZoneNotFoundException ();
 447                         return timeZoneInfo;
 448 #elif LIBC
 449                         string filepath = Path.Combine (TimeZoneDirectory, id);
 450                         return FindSystemTimeZoneByFileName (id, filepath);
 451 #else
 452                         throw new NotImplementedException ();
 453 #endif
 454                 }
 455
 456 #if LIBC
 457                 private static TimeZoneInfo FindSystemTimeZoneByFileName (string id, string filepath)
 458                 {
 459                         if (!File.Exists (filepath))
 460                                 throw new TimeZoneNotFoundException ();
 461
 462                         using (FileStream stream = File.OpenRead (filepath)) {
 463                                 return BuildFromStream (id, stream);
 464                         }
 465                 }
 466 #endif
 467 #if LIBC || MONOTOUCH
 468                 const int BUFFER_SIZE = 16384; //Big enough for any tz file (on Oct 2008, all tz files are under 10k)
 469
 470                 private static TimeZoneInfo BuildFromStream (string id, Stream stream)
 471                 {
 472                         byte [] buffer = new byte [BUFFER_SIZE];
 473                         int length = stream.Read (buffer, 0, BUFFER_SIZE);
 474
 475                         if (!ValidTZFile (buffer, length))
 476                                 throw new InvalidTimeZoneException ("TZ file too big for the buffer");
 477
 478                         try {
 479                                 return ParseTZBuffer (id, buffer, length);
 480                         } catch (Exception e) {
 481                                 throw new InvalidTimeZoneException (e.Message);
 482                         }
 483                 }
 484 #endif
 485
 486 #if !NET_2_1
 487                 private static TimeZoneInfo FromRegistryKey (string id, RegistryKey key)
 488                 {
 489                         byte [] reg_tzi = (byte []) key.GetValue ("TZI");
 490
 491                         if (reg_tzi == null)
 492                                 throw new InvalidTimeZoneException ();
 493
 494                         int bias = BitConverter.ToInt32 (reg_tzi, 0);
 495                         TimeSpan baseUtcOffset = new TimeSpan (0, -bias, 0);
 496
 497                         string display_name = (string) key.GetValue ("Display");
 498                         string standard_name = (string) key.GetValue ("Std");
 499                         string daylight_name = (string) key.GetValue ("Dlt");
 500
 501                         List<AdjustmentRule> adjustmentRules = new List<AdjustmentRule> ();
 502
 503                         RegistryKey dst_key = key.OpenSubKey ("Dynamic DST", false);
 504                         if (dst_key != null) {
 505                                 int first_year = (int) dst_key.GetValue ("FirstEntry");
 506                                 int last_year = (int) dst_key.GetValue ("LastEntry");
 507                                 int year;
 508
 509                                 for (year=first_year; year<=last_year; year++) {
 510                                         byte [] dst_tzi = (byte []) dst_key.GetValue (year.ToString ());
 511                                         if (dst_tzi != null) {
 512                                                 int start_year = year == first_year ? 1 : year;
 513                                                 int end_year = year == last_year ? 9999 : year;
 514                                                 ParseRegTzi(adjustmentRules, start_year, end_year, dst_tzi);
 515                                         }
 516                                 }
 517                         }
 518                         else
 519                                 ParseRegTzi(adjustmentRules, 1, 9999, reg_tzi);
 520
 521                         return CreateCustomTimeZone (id, baseUtcOffset, display_name, standard_name, daylight_name, ValidateRules (adjustmentRules).ToArray ());
 522                 }
 523
 524                 private static void ParseRegTzi (List<AdjustmentRule> adjustmentRules, int start_year, int end_year, byte [] buffer)
 525                 {
 526                         //int standard_bias = BitConverter.ToInt32 (buffer, 4); /* not sure how to handle this */
 527                         int daylight_bias = BitConverter.ToInt32 (buffer, 8);
 528
 529                         int standard_year = BitConverter.ToInt16 (buffer, 12);
 530                         int standard_month = BitConverter.ToInt16 (buffer, 14);
 531                         int standard_dayofweek = BitConverter.ToInt16 (buffer, 16);
 532                         int standard_day = BitConverter.ToInt16 (buffer, 18);
 533                         int standard_hour = BitConverter.ToInt16 (buffer, 20);
 534                         int standard_minute = BitConverter.ToInt16 (buffer, 22);
 535                         int standard_second = BitConverter.ToInt16 (buffer, 24);
 536                         int standard_millisecond = BitConverter.ToInt16 (buffer, 26);
 537
 538                         int daylight_year = BitConverter.ToInt16 (buffer, 28);
 539                         int daylight_month = BitConverter.ToInt16 (buffer, 30);
 540                         int daylight_dayofweek = BitConverter.ToInt16 (buffer, 32);
 541                         int daylight_day = BitConverter.ToInt16 (buffer, 34);
 542                         int daylight_hour = BitConverter.ToInt16 (buffer, 36);
 543                         int daylight_minute = BitConverter.ToInt16 (buffer, 38);
 544                         int daylight_second = BitConverter.ToInt16 (buffer, 40);
 545                         int daylight_millisecond = BitConverter.ToInt16 (buffer, 42);
 546
 547                         if (standard_month == 0 || daylight_month == 0)
 548                                 return;
 549
 550                         DateTime start_date;
 551                         DateTime start_timeofday = new DateTime (1, 1, 1, daylight_hour, daylight_minute, daylight_second, daylight_millisecond);
 552                         TransitionTime start_transition_time;
 553
 554                         if (daylight_year == 0) {
 555                                 start_date = new DateTime (start_year, 1, 1);
 556                                 start_transition_time = TransitionTime.CreateFloatingDateRule (
 557                                         start_timeofday, daylight_month, daylight_day,
 558                                         (DayOfWeek) daylight_dayofweek);
 559                         }
 560                         else {
 561                                 start_date = new DateTime (daylight_year, daylight_month, daylight_day,
 562                                         daylight_hour, daylight_minute, daylight_second, daylight_millisecond);
 563                                 start_transition_time = TransitionTime.CreateFixedDateRule (
 564                                         start_timeofday, daylight_month, daylight_day);
 565                         }
 566
 567                         DateTime end_date;
 568                         DateTime end_timeofday = new DateTime (1, 1, 1, standard_hour, standard_minute, standard_second, standard_millisecond);
 569                         TransitionTime end_transition_time;
 570
 571                         if (standard_year == 0) {
 572                                 end_date = new DateTime (end_year, 12, 31);
 573                                 end_transition_time = TransitionTime.CreateFloatingDateRule (
 574                                         end_timeofday, standard_month, standard_day,
 575                                         (DayOfWeek) standard_dayofweek);
 576                         }
 577                         else {
 578                                 end_date = new DateTime (standard_year, standard_month, standard_day,
 579                                         standard_hour, standard_minute, standard_second, standard_millisecond);
 580                                 end_transition_time = TransitionTime.CreateFixedDateRule (
 581                                         end_timeofday, standard_month, standard_day);
 582                         }
 583
 584                         TimeSpan daylight_delta = new TimeSpan(0, -daylight_bias, 0);
 585
 586                         adjustmentRules.Add (AdjustmentRule.CreateAdjustmentRule (
 587                                 start_date, end_date, daylight_delta,
 588                                 start_transition_time, end_transition_time));
 589                 }
 590 #endif
 591
 592                 public AdjustmentRule [] GetAdjustmentRules ()
 593                 {
 594                         if (!supportsDaylightSavingTime)
 595                                 return new AdjustmentRule [0];
 596                         else
 597                                 return (AdjustmentRule []) adjustmentRules.Clone ();
 598                 }
 599
 600                 public TimeSpan [] GetAmbiguousTimeOffsets (DateTime dateTime)
 601                 {
 602                         if (!IsAmbiguousTime (dateTime))
 603                                 throw new ArgumentException ("dateTime is not an ambiguous time");
 604
 605                         AdjustmentRule rule = GetApplicableRule (dateTime);
 606                         if (rule != null)
 607                                 return new TimeSpan[] {baseUtcOffset, baseUtcOffset + rule.DaylightDelta};
 608                         else
 609                                 return new TimeSpan[] {baseUtcOffset, baseUtcOffset};
 610                 }
 611
 612                 public TimeSpan [] GetAmbiguousTimeOffsets (DateTimeOffset dateTimeOffset)
 613                 {
 614                         if (!IsAmbiguousTime (dateTimeOffset))
 615                                 throw new ArgumentException ("dateTimeOffset is not an ambiguous time");
 616
 617                         throw new NotImplementedException ();
 618                 }
 619
 620                 public override int GetHashCode ()
 621                 {
 622                         int hash_code = Id.GetHashCode ();
 623                         foreach (AdjustmentRule rule in GetAdjustmentRules ())
 624                                 hash_code ^= rule.GetHashCode ();
 625                         return hash_code;
 626                 }
 627
 628                 void ISerializable.GetObjectData (SerializationInfo info, StreamingContext context)
 629                 {
 630                         if (info == null)
 631                                 throw new ArgumentNullException ("info");
 632                         info.AddValue ("Id", id);
 633                         info.AddValue ("DisplayName", displayName);
 634                         info.AddValue ("StandardName", standardDisplayName);
 635                         info.AddValue ("DaylightName", daylightDisplayName);
 636                         info.AddValue ("BaseUtcOffset", baseUtcOffset);
 637                         info.AddValue ("AdjustmentRules", adjustmentRules);
 638                         info.AddValue ("SupportsDaylightSavingTime", SupportsDaylightSavingTime);
 639                 }
 640
 641                 //FIXME: change this to a generic Dictionary and allow caching for FindSystemTimeZoneById
 642                 private static List<TimeZoneInfo> systemTimeZones;
 643                 public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones ()
 644                 {
 645                         if (systemTimeZones == null) {
 646                                 systemTimeZones = new List<TimeZoneInfo> ();
 647 #if !NET_2_1
 648                                 if (TimeZoneKey != null) {
 649                                         foreach (string id in TimeZoneKey.GetSubKeyNames ()) {
 650                                                 try {
 651                                                         systemTimeZones.Add (FindSystemTimeZoneById (id));
 652                                                 } catch {}
 653                                         }
 654
 655                                         return new ReadOnlyCollection<TimeZoneInfo> (systemTimeZones);
 656                                 }
 657 #endif
 658 #if MONODROID
 659                         foreach (string id in AndroidTimeZones.GetAvailableIds ()) {
 660                                 var tz = AndroidTimeZones.GetTimeZone (id, id);
 661                                 if (tz != null)
 662                                         systemTimeZones.Add (tz);
 663                         }
 664 #elif MONOTOUCH
 665                                 if (systemTimeZones.Count == 0) {
 666                                         foreach (string name in GetMonoTouchNames ()) {
 667                                                 using (Stream stream = GetMonoTouchData (name, false)) {
 668                                                         if (stream == null)
 669                                                                 continue;
 670                                                         systemTimeZones.Add (BuildFromStream (name, stream));
 671                                                 }
 672                                         }
 673                                 }
 674 #elif LIBC
 675                                 string[] continents = new string [] {"Africa", "America", "Antarctica", "Arctic", "Asia", "Atlantic", "Brazil", "Canada", "Chile", "Europe", "Indian", "Mexico", "Mideast", "Pacific", "US"};
 676                                 foreach (string continent in continents) {
 677                                         try {
 678                                                 foreach (string zonepath in Directory.GetFiles (Path.Combine (TimeZoneDirectory, continent))) {
 679                                                         try {
 680                                                                 string id = String.Format ("{0}/{1}", continent, Path.GetFileName (zonepath));
 681                                                                 systemTimeZones.Add (FindSystemTimeZoneById (id));
 682                                                         } catch (ArgumentNullException) {
 683                                                         } catch (TimeZoneNotFoundException) {
 684                                                         } catch (InvalidTimeZoneException) {
 685                                                         } catch (Exception) {
 686                                                                 throw;
 687                                                         }
 688                                                 }
 689                                         } catch {}
 690                                 }
 691 #else
 692                                 throw new NotImplementedException ("This method is not implemented for this platform");
 693 #endif
 694                         }
 695                         return new ReadOnlyCollection<TimeZoneInfo> (systemTimeZones);
 696                 }
 697
 698                 public TimeSpan GetUtcOffset (DateTime dateTime)
 699                 {
 700                         bool isDST;
 701                         return GetUtcOffset (dateTime, out isDST);
 702                 }
 703
 704                 public TimeSpan GetUtcOffset (DateTimeOffset dateTimeOffset)
 705                 {
 706                         throw new NotImplementedException ();
 707                 }
 708
 709                 private TimeSpan GetUtcOffset (DateTime dateTime, out bool isDST)
 710                 {
 711                         isDST = false;
 712
 713                         TimeZoneInfo tz = this;
 714                         if (dateTime.Kind == DateTimeKind.Utc)
 715                                 tz = TimeZoneInfo.Utc;
 716
 717                         if (dateTime.Kind == DateTimeKind.Local)
 718                                 tz = TimeZoneInfo.Local;
 719
 720                         bool isTzDst;
 721                         var tzOffset = GetUtcOffsetHelper (dateTime, tz, out isTzDst);
 722
 723                         if (tz == this) {
 724                                 isDST = isTzDst;
 725                                 return tzOffset;
 726                         }
 727
 728                         DateTime utcDateTime;
 729                         if (!TryAddTicks (dateTime, -tzOffset.Ticks, out utcDateTime, DateTimeKind.Utc))
 730                                 return BaseUtcOffset;
 731
 732                         return GetUtcOffsetHelper (utcDateTime, this, out isDST);
 733                 }
 734
 735                 // This is an helper method used by the method above, do not use this on its own.
 736                 private static TimeSpan GetUtcOffsetHelper (DateTime dateTime, TimeZoneInfo tz, out bool isDST)
 737                 {
 738                         if (dateTime.Kind == DateTimeKind.Local && tz != TimeZoneInfo.Local)
 739                                 throw new Exception ();
 740
 741                         isDST = false;
 742
 743                         if (tz == TimeZoneInfo.Utc)
 744                                 return TimeSpan.Zero;
 745
 746                         TimeSpan offset;
 747                         if (tz.TryGetTransitionOffset(dateTime, out offset, out isDST))
 748                                 return offset;
 749
 750                         if (dateTime.Kind == DateTimeKind.Utc) {
 751                                 var utcRule = tz.GetApplicableRule (dateTime);
 752                                 if (utcRule != null && tz.IsInDST (utcRule, dateTime)) {
 753                                         isDST = true;
 754                                         return tz.BaseUtcOffset + utcRule.DaylightDelta;
 755                                 }
 756
 757                                 return tz.BaseUtcOffset;
 758                         }
 759
 760                         DateTime stdUtcDateTime;
 761                         if (!TryAddTicks (dateTime, -tz.BaseUtcOffset.Ticks, out stdUtcDateTime, DateTimeKind.Utc))
 762                                 return tz.BaseUtcOffset;
 763
 764                         var tzRule = tz.GetApplicableRule (stdUtcDateTime);
 765
 766                         DateTime dstUtcDateTime = DateTime.MinValue;
 767                         if (tzRule != null) {
 768                                 if (!TryAddTicks (stdUtcDateTime, -tzRule.DaylightDelta.Ticks, out dstUtcDateTime, DateTimeKind.Utc))
 769                                         return tz.BaseUtcOffset;
 770                         }
 771
 772                         if (tzRule != null && tz.IsInDST (tzRule, stdUtcDateTime) && tz.IsInDST (tzRule, dstUtcDateTime)) {
 773                                 isDST = true;
 774                                 return tz.BaseUtcOffset + tzRule.DaylightDelta;
 775                         }
 776
 777                         return tz.BaseUtcOffset;
 778                 }
 779
 780                 public bool HasSameRules (TimeZoneInfo other)
 781                 {
 782                         if (other == null)
 783                                 throw new ArgumentNullException ("other");
 784
 785                         if ((this.adjustmentRules == null) != (other.adjustmentRules == null))
 786                                 return false;
 787
 788                         if (this.adjustmentRules == null)
 789                                 return true;
 790
 791                         if (this.BaseUtcOffset != other.BaseUtcOffset)
 792                                 return false;
 793
 794                         if (this.adjustmentRules.Length != other.adjustmentRules.Length)
 795                                 return false;
 796
 797                         for (int i = 0; i < adjustmentRules.Length; i++) {
 798                                 if (! (this.adjustmentRules [i]).Equals (other.adjustmentRules [i]))
 799                                         return false;
 800                         }
 801
 802                         return true;
 803                 }
 804
 805                 public bool IsAmbiguousTime (DateTime dateTime)
 806                 {
 807                         if (dateTime.Kind == DateTimeKind.Local && IsInvalidTime (dateTime))
 808                                 throw new ArgumentException ("Kind is Local and time is Invalid");
 809
 810                         if (this == TimeZoneInfo.Utc)
 811                                 return false;
 812
 813                         if (dateTime.Kind == DateTimeKind.Utc)
 814                                 dateTime = ConvertTimeFromUtc (dateTime);
 815
 816                         if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local)
 817                                 dateTime = ConvertTime (dateTime, TimeZoneInfo.Local, this);
 818
 819                         AdjustmentRule rule = GetApplicableRule (dateTime);
 820                         if (rule != null) {
 821                                 DateTime tpoint = TransitionPoint (rule.DaylightTransitionEnd, dateTime.Year);
 822                                 if (dateTime > tpoint - rule.DaylightDelta  && dateTime <= tpoint)
 823                                         return true;
 824                         }
 825
 826                         return false;
 827                 }
 828
 829                 public bool IsAmbiguousTime (DateTimeOffset dateTimeOffset)
 830                 {
 831                         throw new NotImplementedException ();
 832                 }
 833
 834                 private bool IsInDST (AdjustmentRule rule, DateTime dateTime)
 835                 {
 836                         // Check whether we're in the dateTime year's DST period
 837                         if (IsInDSTForYear (rule, dateTime, dateTime.Year))
 838                                 return true;
 839
 840                         // We might be in the dateTime previous year's DST period
 841                         return IsInDSTForYear (rule, dateTime, dateTime.Year - 1);
 842                 }
 843
 844                 bool IsInDSTForYear (AdjustmentRule rule, DateTime dateTime, int year)
 845                 {
 846                         DateTime DST_start = TransitionPoint (rule.DaylightTransitionStart, year);
 847                         DateTime DST_end = TransitionPoint (rule.DaylightTransitionEnd, year + ((rule.DaylightTransitionStart.Month < rule.DaylightTransitionEnd.Month) ? 0 : 1));
 848                         if (dateTime.Kind == DateTimeKind.Utc) {
 849                                 DST_start -= BaseUtcOffset;
 850                                 DST_end -= (BaseUtcOffset + rule.DaylightDelta);
 851                         }
 852
 853                         return (dateTime >= DST_start && dateTime < DST_end);
 854                 }
 855
 856                 public bool IsDaylightSavingTime (DateTime dateTime)
 857                 {
 858                         if (dateTime.Kind == DateTimeKind.Local && IsInvalidTime (dateTime))
 859                                 throw new ArgumentException ("dateTime is invalid and Kind is Local");
 860
 861                         if (this == TimeZoneInfo.Utc)
 862                                 return false;
 863
 864                         if (!SupportsDaylightSavingTime)
 865                                 return false;
 866
 867                         bool isDst;
 868                         GetUtcOffset (dateTime, out isDst);
 869
 870                         return isDst;
 871                 }
 872
 873                 internal bool IsDaylightSavingTime (DateTime dateTime, TimeZoneInfoOptions flags)
 874                 {
 875                         return IsDaylightSavingTime (dateTime);
 876                 }
 877
 878                 public bool IsDaylightSavingTime (DateTimeOffset dateTimeOffset)
 879                 {
 880                         throw new NotImplementedException ();
 881                 }
 882
 883                 public bool IsInvalidTime (DateTime dateTime)
 884                 {
 885                         if (dateTime.Kind == DateTimeKind.Utc)
 886                                 return false;
 887                         if (dateTime.Kind == DateTimeKind.Local && this != Local)
 888                                 return false;
 889
 890                         AdjustmentRule rule = GetApplicableRule (dateTime);
 891                         if (rule != null) {
 892                                 DateTime tpoint = TransitionPoint (rule.DaylightTransitionStart, dateTime.Year);
 893                                 if (dateTime >= tpoint && dateTime < tpoint + rule.DaylightDelta)
 894                                         return true;
 895                         }
 896
 897                         return false;
 898                 }
 899
 900                 void IDeserializationCallback.OnDeserialization (object sender)
 901                 {
 902                         try {
 903                                         TimeZoneInfo.Validate (id, baseUtcOffset, adjustmentRules);
 904                                 } catch (ArgumentException ex) {
 905                                         throw new SerializationException ("invalid serialization data", ex);
 906                                 }
 907                 }
 908
 909                 private static void Validate (string id, TimeSpan baseUtcOffset, AdjustmentRule [] adjustmentRules)
 910                 {
 911                         if (id == null)
 912                                 throw new ArgumentNullException ("id");
 913
 914                         if (id == String.Empty)
 915                                 throw new ArgumentException ("id parameter is an empty string");
 916
 917                         if (baseUtcOffset.Ticks % TimeSpan.TicksPerMinute != 0)
 918                                 throw new ArgumentException ("baseUtcOffset parameter does not represent a whole number of minutes");
 919
 920                         if (baseUtcOffset > new TimeSpan (14, 0, 0) || baseUtcOffset < new TimeSpan (-14, 0, 0))
 921                                 throw new ArgumentOutOfRangeException ("baseUtcOffset parameter is greater than 14 hours or less than -14 hours");
 922
 923 #if STRICT
 924                         if (id.Length > 32)
 925                                 throw new ArgumentException ("id parameter shouldn't be longer than 32 characters");
 926 #endif
 927
 928                         if (adjustmentRules != null && adjustmentRules.Length != 0) {
 929                                 AdjustmentRule prev = null;
 930                                 foreach (AdjustmentRule current in adjustmentRules) {
 931                                         if (current == null)
 932                                                 throw new InvalidTimeZoneException ("one or more elements in adjustmentRules are null");
 933
 934                                         if ((baseUtcOffset + current.DaylightDelta < new TimeSpan (-14, 0, 0)) ||
 935                                                         (baseUtcOffset + current.DaylightDelta > new TimeSpan (14, 0, 0)))
 936                                                 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;");
 937
 938                                         if (prev != null && prev.DateStart > current.DateStart)
 939                                                 throw new InvalidTimeZoneException ("adjustment rules specified in adjustmentRules parameter are not in chronological order");
 940
 941                                         if (prev != null && prev.DateEnd > current.DateStart)
 942                                                 throw new InvalidTimeZoneException ("some adjustment rules in the adjustmentRules parameter overlap");
 943
 944                                         if (prev != null && prev.DateEnd == current.DateStart)
 945                                                 throw new InvalidTimeZoneException ("a date can have multiple adjustment rules applied to it");
 946
 947                                         prev = current;
 948                                 }
 949                         }
 950                 }
 951
 952                 public override string ToString ()
 953                 {
 954                         return DisplayName;
 955                 }
 956
 957                 private TimeZoneInfo (SerializationInfo info, StreamingContext context)
 958                 {
 959                         if (info == null)
 960                                 throw new ArgumentNullException ("info");
 961                         id = (string) info.GetValue ("Id", typeof (string));
 962                         displayName = (string) info.GetValue ("DisplayName", typeof (string));
 963                         standardDisplayName = (string) info.GetValue ("StandardName", typeof (string));
 964                         daylightDisplayName = (string) info.GetValue ("DaylightName", typeof (string));
 965                         baseUtcOffset = (TimeSpan) info.GetValue ("BaseUtcOffset", typeof (TimeSpan));
 966                         adjustmentRules = (TimeZoneInfo.AdjustmentRule []) info.GetValue ("AdjustmentRules", typeof (TimeZoneInfo.AdjustmentRule []));
 967                         supportsDaylightSavingTime = (bool) info.GetValue ("SupportsDaylightSavingTime", typeof (bool));
 968                 }
 969
 970                 private TimeZoneInfo (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules, bool disableDaylightSavingTime)
 971                 {
 972                         if (id == null)
 973                                 throw new ArgumentNullException ("id");
 974
 975                         if (id == String.Empty)
 976                                 throw new ArgumentException ("id parameter is an empty string");
 977
 978                         if (baseUtcOffset.Ticks % TimeSpan.TicksPerMinute != 0)
 979                                 throw new ArgumentException ("baseUtcOffset parameter does not represent a whole number of minutes");
 980
 981                         if (baseUtcOffset > new TimeSpan (14, 0, 0) || baseUtcOffset < new TimeSpan (-14, 0, 0))
 982                                 throw new ArgumentOutOfRangeException ("baseUtcOffset parameter is greater than 14 hours or less than -14 hours");
 983
 984 #if STRICT
 985                         if (id.Length > 32)
 986                                 throw new ArgumentException ("id parameter shouldn't be longer than 32 characters");
 987 #endif
 988
 989                         bool supportsDaylightSavingTime = !disableDaylightSavingTime;
 990
 991                         if (adjustmentRules != null && adjustmentRules.Length != 0) {
 992                                 AdjustmentRule prev = null;
 993                                 foreach (AdjustmentRule current in adjustmentRules) {
 994                                         if (current == null)
 995                                                 throw new InvalidTimeZoneException ("one or more elements in adjustmentRules are null");
 996
 997                                         if ((baseUtcOffset + current.DaylightDelta < new TimeSpan (-14, 0, 0)) ||
 998                                                         (baseUtcOffset + current.DaylightDelta > new TimeSpan (14, 0, 0)))
 999                                                 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;");
1000
1001                                         if (prev != null && prev.DateStart > current.DateStart)
1002                                                 throw new InvalidTimeZoneException ("adjustment rules specified in adjustmentRules parameter are not in chronological order");
1003
1004                                         if (prev != null && prev.DateEnd > current.DateStart)
1005                                                 throw new InvalidTimeZoneException ("some adjustment rules in the adjustmentRules parameter overlap");
1006
1007                                         if (prev != null && prev.DateEnd == current.DateStart)
1008                                                 throw new InvalidTimeZoneException ("a date can have multiple adjustment rules applied to it");
1009
1010                                         prev = current;
1011                                 }
1012                         } else {
1013                                 supportsDaylightSavingTime = false;
1014                         }
1015
1016                         this.id = id;
1017                         this.baseUtcOffset = baseUtcOffset;
1018                         this.displayName = displayName ?? id;
1019                         this.standardDisplayName = standardDisplayName ?? id;
1020                         this.daylightDisplayName = daylightDisplayName;
1021                         this.supportsDaylightSavingTime = supportsDaylightSavingTime;
1022                         this.adjustmentRules = adjustmentRules;
1023                 }
1024
1025                 private AdjustmentRule GetApplicableRule (DateTime dateTime)
1026                 {
1027                         //Applicable rules are in standard time
1028                         DateTime date = dateTime;
1029
1030                         if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local) {
1031                                 if (!TryAddTicks (date.ToUniversalTime (), BaseUtcOffset.Ticks, out date))
1032                                         return null;
1033                         } else if (dateTime.Kind == DateTimeKind.Utc && this != TimeZoneInfo.Utc) {
1034                                 if (!TryAddTicks (date, BaseUtcOffset.Ticks, out date))
1035                                         return null;
1036                         }
1037
1038                         // get the date component of the datetime
1039                         date = date.Date;
1040
1041                         if (adjustmentRules != null) {
1042                                 foreach (AdjustmentRule rule in adjustmentRules) {
1043                                         if (rule.DateStart > date)
1044                                                 return null;
1045                                         if (rule.DateEnd < date)
1046                                                 continue;
1047                                         return rule;
1048                                 }
1049                         }
1050                         return null;
1051                 }
1052
1053                 private bool TryGetTransitionOffset (DateTime dateTime, out TimeSpan offset,out bool isDst)
1054                 {
1055                         offset = BaseUtcOffset;
1056                         isDst = false;
1057
1058                         if (transitions == null)
1059                                 return false;
1060
1061                         //Transitions are in UTC
1062                         DateTime date = dateTime;
1063
1064                         if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local) {
1065                                 if (!TryAddTicks (date.ToUniversalTime (), BaseUtcOffset.Ticks, out date, DateTimeKind.Utc))
1066                                         return false;
1067                         }
1068
1069                         if (dateTime.Kind != DateTimeKind.Utc) {
1070                                 if (!TryAddTicks (date, -BaseUtcOffset.Ticks, out date, DateTimeKind.Utc))
1071                                         return false;
1072                         }
1073
1074                         for (var i =  transitions.Count - 1; i >= 0; i--) {
1075                                 var pair = transitions [i];
1076                                 DateTime ttime = pair.Key;
1077                                 TimeType ttype = pair.Value;
1078
1079                                 if (ttime > date)
1080                                         continue;
1081
1082                                 offset =  new TimeSpan (0, 0, ttype.Offset);
1083                                 isDst = ttype.IsDst;
1084
1085                                 return true;
1086                         }
1087
1088                         return false;
1089                 }
1090
1091                 private static DateTime TransitionPoint (TransitionTime transition, int year)
1092                 {
1093                         if (transition.IsFixedDateRule)
1094                                 return new DateTime (year, transition.Month, transition.Day) + transition.TimeOfDay.TimeOfDay;
1095
1096                         DayOfWeek first = (new DateTime (year, transition.Month, 1)).DayOfWeek;
1097                         int day = 1 + (transition.Week - 1) * 7 + (transition.DayOfWeek - first + 7) % 7;
1098                         if (day >  DateTime.DaysInMonth (year, transition.Month))
1099                                 day -= 7;
1100                         if (day < 1)
1101                                 day += 7;
1102                         return new DateTime (year, transition.Month, day) + transition.TimeOfDay.TimeOfDay;
1103                 }
1104
1105                 static List<AdjustmentRule> ValidateRules (List<AdjustmentRule> adjustmentRules)
1106                 {
1107                         AdjustmentRule prev = null;
1108                         foreach (AdjustmentRule current in adjustmentRules.ToArray ()) {
1109                                 if (prev != null && prev.DateEnd > current.DateStart) {
1110                                         adjustmentRules.Remove (current);
1111                                 }
1112                                 prev = current;
1113                         }
1114                         return adjustmentRules;
1115                 }
1116
1117 #if LIBC || MONODROID
1118                 private static bool ValidTZFile (byte [] buffer, int length)
1119                 {
1120                         StringBuilder magic = new StringBuilder ();
1121
1122                         for (int i = 0; i < 4; i++)
1123                                 magic.Append ((char)buffer [i]);
1124
1125                         if (magic.ToString () != "TZif")
1126                                 return false;
1127
1128                         if (length >= BUFFER_SIZE)
1129                                 return false;
1130
1131                         return true;
1132                 }
1133
1134                 static int SwapInt32 (int i)
1135                 {
1136                         return (((i >> 24) & 0xff)
1137                                 | ((i >> 8) & 0xff00)
1138                                 | ((i << 8) & 0xff0000)
1139                                 | ((i << 24)));
1140                 }
1141
1142                 static int ReadBigEndianInt32 (byte [] buffer, int start)
1143                 {
1144                         int i = BitConverter.ToInt32 (buffer, start);
1145                         if (!BitConverter.IsLittleEndian)
1146                                 return i;
1147
1148                         return SwapInt32 (i);
1149                 }
1150
1151                 private static TimeZoneInfo ParseTZBuffer (string id, byte [] buffer, int length)
1152                 {
1153                         //Reading the header. 4 bytes for magic, 16 are reserved
1154                         int ttisgmtcnt = ReadBigEndianInt32 (buffer, 20);
1155                         int ttisstdcnt = ReadBigEndianInt32 (buffer, 24);
1156                         int leapcnt = ReadBigEndianInt32 (buffer, 28);
1157                         int timecnt = ReadBigEndianInt32 (buffer, 32);
1158                         int typecnt = ReadBigEndianInt32 (buffer, 36);
1159                         int charcnt = ReadBigEndianInt32 (buffer, 40);
1160
1161                         if (length < 44 + timecnt * 5 + typecnt * 6 + charcnt + leapcnt * 8 + ttisstdcnt + ttisgmtcnt)
1162                                 throw new InvalidTimeZoneException ();
1163
1164                         Dictionary<int, string> abbreviations = ParseAbbreviations (buffer, 44 + 4 * timecnt + timecnt + 6 * typecnt, charcnt);
1165                         Dictionary<int, TimeType> time_types = ParseTimesTypes (buffer, 44 + 4 * timecnt + timecnt, typecnt, abbreviations);
1166                         List<KeyValuePair<DateTime, TimeType>> transitions = ParseTransitions (buffer, 44, timecnt, time_types);
1167
1168                         if (time_types.Count == 0)
1169                                 throw new InvalidTimeZoneException ();
1170
1171                         if (time_types.Count == 1 && ((TimeType)time_types[0]).IsDst)
1172                                 throw new InvalidTimeZoneException ();
1173
1174                         TimeSpan baseUtcOffset = new TimeSpan (0);
1175                         TimeSpan dstDelta = new TimeSpan (0);
1176                         string standardDisplayName = null;
1177                         string daylightDisplayName = null;
1178                         bool dst_observed = false;
1179                         DateTime dst_start = DateTime.MinValue;
1180                         List<AdjustmentRule> adjustmentRules = new List<AdjustmentRule> ();
1181                         bool storeTransition = false;
1182
1183                         for (int i = 0; i < transitions.Count; i++) {
1184                                 var pair = transitions [i];
1185                                 DateTime ttime = pair.Key;
1186                                 TimeType ttype = pair.Value;
1187                                 if (!ttype.IsDst) {
1188                                         if (standardDisplayName != ttype.Name)
1189                                                 standardDisplayName = ttype.Name;
1190                                         if (baseUtcOffset.TotalSeconds != ttype.Offset) {
1191                                                 baseUtcOffset = new TimeSpan (0, 0, ttype.Offset);
1192                                                 if (adjustmentRules.Count > 0) // We ignore AdjustmentRules but store transitions.
1193                                                         storeTransition = true;
1194                                                 adjustmentRules = new List<AdjustmentRule> ();
1195                                                 dst_observed = false;
1196                                         }
1197                                         if (dst_observed) {
1198                                                 //FIXME: check additional fields for this:
1199                                                 //most of the transitions are expressed in GMT
1200                                                 dst_start += baseUtcOffset;
1201                                                 DateTime dst_end = ttime + baseUtcOffset + dstDelta;
1202
1203                                                 //some weird timezone (America/Phoenix) have end dates on Jan 1st
1204                                                 if (dst_end.Date == new DateTime (dst_end.Year, 1, 1) && dst_end.Year > dst_start.Year)
1205                                                         dst_end -= new TimeSpan (24, 0, 0);
1206
1207                                                 /*
1208                                                  * AdjustmentRule specifies a DST period that starts and ends within a year.
1209                                                  * When we have a DST period longer than a year, the generated AdjustmentRule may not be usable.
1210                                                  * Thus we fallback to the transitions.
1211                                                  */
1212                                                 if (dst_start.AddYears (1) < dst_end)
1213                                                         storeTransition = true;
1214
1215                                                 DateTime dateStart, dateEnd;
1216                                                 if (dst_start.Month < 7)
1217                                                         dateStart = new DateTime (dst_start.Year, 1, 1);
1218                                                 else
1219                                                         dateStart = new DateTime (dst_start.Year, 7, 1);
1220
1221                                                 if (dst_end.Month >= 7)
1222                                                         dateEnd = new DateTime (dst_end.Year, 12, 31);
1223                                                 else
1224                                                         dateEnd = new DateTime (dst_end.Year, 6, 30);
1225
1226
1227                                                 TransitionTime transition_start = TransitionTime.CreateFixedDateRule (new DateTime (1, 1, 1) + dst_start.TimeOfDay, dst_start.Month, dst_start.Day);
1228                                                 TransitionTime transition_end = TransitionTime.CreateFixedDateRule (new DateTime (1, 1, 1) + dst_end.TimeOfDay, dst_end.Month, dst_end.Day);
1229                                                 if  (transition_start != transition_end) //y, that happened in Argentina in 1943-1946
1230                                                         adjustmentRules.Add (AdjustmentRule.CreateAdjustmentRule (dateStart, dateEnd, dstDelta, transition_start, transition_end));
1231                                         }
1232                                         dst_observed = false;
1233                                 } else {
1234                                         if (daylightDisplayName != ttype.Name)
1235                                                 daylightDisplayName = ttype.Name;
1236                                         if (dstDelta.TotalSeconds != ttype.Offset - baseUtcOffset.TotalSeconds)
1237                                                 dstDelta = new TimeSpan(0, 0, ttype.Offset) - baseUtcOffset;
1238
1239                                         dst_start = ttime;
1240                                         dst_observed = true;
1241                                 }
1242                         }
1243
1244                         TimeZoneInfo tz;
1245                         if (adjustmentRules.Count == 0 && !storeTransition) {
1246                                 TimeType t = (TimeType)time_types [0];
1247                                 if (standardDisplayName == null) {
1248                                         standardDisplayName = t.Name;
1249                                         baseUtcOffset = new TimeSpan (0, 0, t.Offset);
1250                                 }
1251                                 tz = CreateCustomTimeZone (id, baseUtcOffset, id, standardDisplayName);
1252                         } else {
1253                                 tz = CreateCustomTimeZone (id, baseUtcOffset, id, standardDisplayName, daylightDisplayName, ValidateRules (adjustmentRules).ToArray ());
1254                         }
1255
1256                         if (storeTransition)
1257                                 tz.transitions = transitions;
1258
1259                         return tz;
1260                 }
1261
1262                 static Dictionary<int, string> ParseAbbreviations (byte [] buffer, int index, int count)
1263                 {
1264                         var abbrevs = new Dictionary<int, string> ();
1265                         int abbrev_index = 0;
1266                         var sb = new StringBuilder ();
1267                         for (int i = 0; i < count; i++) {
1268                                 char c = (char) buffer [index + i];
1269                                 if (c != '\0')
1270                                         sb.Append (c);
1271                                 else {
1272                                         abbrevs.Add (abbrev_index, sb.ToString ());
1273                                         //Adding all the substrings too, as it seems to be used, at least for Africa/Windhoek
1274                                         for (int j = 1; j < sb.Length; j++)
1275                                                 abbrevs.Add (abbrev_index + j, sb.ToString (j, sb.Length - j));
1276                                         abbrev_index = i + 1;
1277                                         sb = new StringBuilder ();
1278                                 }
1279                         }
1280                         return abbrevs;
1281                 }
1282
1283                 static Dictionary<int, TimeType> ParseTimesTypes (byte [] buffer, int index, int count, Dictionary<int, string> abbreviations)
1284                 {
1285                         var types = new Dictionary<int, TimeType> (count);
1286                         for (int i = 0; i < count; i++) {
1287                                 int offset = ReadBigEndianInt32 (buffer, index + 6 * i);
1288                                 byte is_dst = buffer [index + 6 * i + 4];
1289                                 byte abbrev = buffer [index + 6 * i + 5];
1290                                 types.Add (i, new TimeType (offset, (is_dst != 0), abbreviations [(int)abbrev]));
1291                         }
1292                         return types;
1293                 }
1294
1295                 static List<KeyValuePair<DateTime, TimeType>> ParseTransitions (byte [] buffer, int index, int count, Dictionary<int, TimeType> time_types)
1296                 {
1297                         var list = new List<KeyValuePair<DateTime, TimeType>> (count);
1298                         for (int i = 0; i < count; i++) {
1299                                 int unixtime = ReadBigEndianInt32 (buffer, index + 4 * i);
1300                                 DateTime ttime = DateTimeFromUnixTime (unixtime);
1301                                 byte ttype = buffer [index + 4 * count + i];
1302                                 list.Add (new KeyValuePair<DateTime, TimeType> (ttime, time_types [(int)ttype]));
1303                         }
1304                         return list;
1305                 }
1306
1307                 static DateTime DateTimeFromUnixTime (long unix_time)
1308                 {
1309                         DateTime date_time = new DateTime (1970, 1, 1);
1310                         return date_time.AddSeconds (unix_time);
1311                 }
1312
1313 #region reference sources
1314                 // Shortcut for TimeZoneInfo.Local.GetUtcOffset
1315                 internal static TimeSpan GetLocalUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
1316                 {
1317                         bool dst;
1318                         return Local.GetUtcOffset (dateTime, out dst);
1319                 }
1320
1321                 internal TimeSpan GetUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
1322                 {
1323                         bool dst;
1324                         return GetUtcOffset (dateTime, out dst);
1325                 }
1326
1327                 static internal TimeSpan GetUtcOffsetFromUtc (DateTime time, TimeZoneInfo zone, out Boolean isDaylightSavings, out Boolean isAmbiguousLocalDst)
1328                 {
1329                         isDaylightSavings = false;
1330                         isAmbiguousLocalDst = false;
1331                         TimeSpan baseOffset = zone.BaseUtcOffset;
1332
1333                         if (zone.IsAmbiguousTime (time)) {
1334                                 isAmbiguousLocalDst = true;
1335                                 return baseOffset;
1336                         }
1337
1338                         return zone.GetUtcOffset (time, out isDaylightSavings);
1339                 }
1340 #endregion
1341         }
1342
1343         struct TimeType {
1344                 public readonly int Offset;
1345                 public readonly bool IsDst;
1346                 public string Name;
1347
1348                 public TimeType (int offset, bool is_dst, string abbrev)
1349                 {
1350                         this.Offset = offset;
1351                         this.IsDst = is_dst;
1352                         this.Name = abbrev;
1353                 }
1354
1355                 public override string ToString ()
1356                 {
1357                         return "offset: " + Offset + "s, is_dst: " + IsDst + ", zone name: " + Name;
1358                 }
1359 #else
1360         }
1361 #endif
1362         }
1363 }