[corlib] TimeZoneInfo.ConvertTimeToUtc maximum datetime handling

[mono.git] / mcs / class / corlib / System / TimeZoneInfo.cs

/*
 * System.TimeZoneInfo
 *
 * Author(s)
 *      Stephane Delcroix <stephane@delcroix.org>
 *
 * Copyright 2011 Xamarin Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

using System;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Runtime.Serialization;
using System.Text;
using System.Globalization;

#if LIBC || MONODROID
using System.IO;
using Mono;
#endif

using Microsoft.Win32;

namespace System
{
#if MOBILE
        [TypeForwardedFrom (Consts.AssemblySystem_Core)]
#else
        [TypeForwardedFrom (Consts.AssemblySystemCore_3_5)]
#endif
        [SerializableAttribute]
        public
        sealed partial class TimeZoneInfo : IEquatable<TimeZoneInfo>, ISerializable, IDeserializationCallback
        {
                TimeSpan baseUtcOffset;
                public TimeSpan BaseUtcOffset {
                        get { return baseUtcOffset; }
                }

                string daylightDisplayName;
                public string DaylightName {
                        get { 
                                return supportsDaylightSavingTime
                                        ? daylightDisplayName
                                        : string.Empty;
                        }
                }

                string displayName;
                public string DisplayName {
                        get { return displayName; }
                }

                string id;
                public string Id {
                        get { return id; }
                }

                static TimeZoneInfo local;
                public static TimeZoneInfo Local {
                        get { 
                                var l = local;
                                if (l == null) {
                                        l = CreateLocal ();
                                        if (l == null)
                                                throw new TimeZoneNotFoundException ();

                                        if (Interlocked.CompareExchange (ref local, l, null) != null)
                                                l = local;
                                }

                                return l;
                        }
                }

                /*
                        TimeZone transitions are stored when there is a change on the base offset.
                */
                private List<KeyValuePair<DateTime, TimeType>> transitions;

                static TimeZoneInfo CreateLocal ()
                {
#if MONODROID
                        return AndroidTimeZones.Local;
#elif MONOTOUCH
                        using (Stream stream = GetMonoTouchData (null)) {
                                return BuildFromStream ("Local", stream);
                        }
#else
#if !NET_2_1
                        if (IsWindows && LocalZoneKey != null) {
                                string name = (string)LocalZoneKey.GetValue ("TimeZoneKeyName");
                                name = TrimSpecial (name);
                                if (name != null)
                                        return TimeZoneInfo.FindSystemTimeZoneById (name);
                        }
#endif

                        var tz = Environment.GetEnvironmentVariable ("TZ");
                        if (tz != null) {
                                if (tz == String.Empty)
                                        return Utc;
                                try {
                                        return FindSystemTimeZoneByFileName (tz, Path.Combine (TimeZoneDirectory, tz));
                                } catch {
                                        return Utc;
                                }
                        }

                        try {
                                return FindSystemTimeZoneByFileName ("Local", "/etc/localtime");        
                        } catch {
                                try {
                                        return FindSystemTimeZoneByFileName ("Local", Path.Combine (TimeZoneDirectory, "localtime"));   
                                } catch {
                                        return null;
                                }
                        }
#endif
                }

                string standardDisplayName;
                public string StandardName {
                        get { return standardDisplayName; }
                }

                bool supportsDaylightSavingTime;
                public bool SupportsDaylightSavingTime {
                        get  { return supportsDaylightSavingTime; }
                }

                static TimeZoneInfo utc;
                public static TimeZoneInfo Utc {
                        get {
                                if (utc == null)
                                        utc = CreateCustomTimeZone ("UTC", new TimeSpan (0), "UTC", "UTC");
                                return utc;
                        }
                }
#if LIBC
                static string timeZoneDirectory;
                static string TimeZoneDirectory {
                        get {
                                if (timeZoneDirectory == null)
                                        timeZoneDirectory = "/usr/share/zoneinfo";
                                return timeZoneDirectory;
                        }
                        set {
                                ClearCachedData ();
                                timeZoneDirectory = value;
                        }
                }
#endif
                private AdjustmentRule [] adjustmentRules;

#if !NET_2_1
                /// <summary>
                /// Determine whether windows of not (taken Stephane Delcroix's code)
                /// </summary>
                private static bool IsWindows
                {
                        get {
                                int platform = (int) Environment.OSVersion.Platform;
                                return ((platform != 4) && (platform != 6) && (platform != 128));
                        }
                }
                
                /// <summary>
                /// Needed to trim misc garbage in MS registry keys
                /// </summary>
                private static string TrimSpecial (string str)
                {
                        var Istart = 0;
                        while (Istart < str.Length && !char.IsLetterOrDigit(str[Istart])) Istart++;
                        var Iend = str.Length - 1;
                        while (Iend > Istart && !char.IsLetterOrDigit(str[Iend])) Iend--;
                        
                        return str.Substring (Istart, Iend-Istart+1);
                }
                
                static RegistryKey timeZoneKey;
                static RegistryKey TimeZoneKey {
                        get {
                                if (timeZoneKey != null)
                                        return timeZoneKey;
                                if (!IsWindows)
                                        return null;
                                
                                return timeZoneKey = Registry.LocalMachine.OpenSubKey (
                                        "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones",
                                        false);
                        }
                }
                
                static RegistryKey localZoneKey;
                static RegistryKey LocalZoneKey {
                        get {
                                if (localZoneKey != null)
                                        return localZoneKey;
                                
                                if (!IsWindows)
                                        return null;
                                
                                return localZoneKey = Registry.LocalMachine.OpenSubKey (
                                        "SYSTEM\\CurrentControlSet\\Control\\TimeZoneInformation", false);
                        }
                }
#endif

                public static void ClearCachedData ()
                {
                        local = null;
                        utc = null;
                        systemTimeZones = null;
                }

                public static DateTime ConvertTime (DateTime dateTime, TimeZoneInfo destinationTimeZone)
                {
                        return ConvertTime (dateTime, dateTime.Kind == DateTimeKind.Utc ? TimeZoneInfo.Utc : TimeZoneInfo.Local, destinationTimeZone);
                }

                public static DateTime ConvertTime (DateTime dateTime, TimeZoneInfo sourceTimeZone, TimeZoneInfo destinationTimeZone)
                {
                        if (sourceTimeZone == null)
                                throw new ArgumentNullException ("sourceTimeZone");

                        if (destinationTimeZone == null)
                                throw new ArgumentNullException ("destinationTimeZone");
                        
                        if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone != TimeZoneInfo.Local)
                                throw new ArgumentException ("Kind property of dateTime is Local but the sourceTimeZone does not equal TimeZoneInfo.Local");

                        if (dateTime.Kind == DateTimeKind.Utc && sourceTimeZone != TimeZoneInfo.Utc)
                                throw new ArgumentException ("Kind property of dateTime is Utc but the sourceTimeZone does not equal TimeZoneInfo.Utc");
                        
                        if (sourceTimeZone.IsInvalidTime (dateTime))
                                throw new ArgumentException ("dateTime parameter is an invalid time");

                        if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone == TimeZoneInfo.Local && destinationTimeZone == TimeZoneInfo.Local)
                                return dateTime;

                        DateTime utc = ConvertTimeToUtc (dateTime, sourceTimeZone);

                        if (destinationTimeZone != TimeZoneInfo.Utc) {
                                utc = ConvertTimeFromUtc (utc, destinationTimeZone);
                                if (dateTime.Kind == DateTimeKind.Unspecified)
                                        return DateTime.SpecifyKind (utc, DateTimeKind.Unspecified);
                        }
                        
                        return utc;
                }

                public static DateTimeOffset ConvertTime(DateTimeOffset dateTimeOffset, TimeZoneInfo destinationTimeZone) 
                {
                        if (destinationTimeZone == null) 
                                throw new ArgumentNullException("destinationTimeZone");
                
                        var utcDateTime = dateTimeOffset.UtcDateTime;
                        AdjustmentRule rule = destinationTimeZone.GetApplicableRule (utcDateTime);
                
                        if (rule != null && destinationTimeZone.IsDaylightSavingTime(utcDateTime)) {
                                var offset = destinationTimeZone.BaseUtcOffset + rule.DaylightDelta;
                                return new DateTimeOffset(DateTime.SpecifyKind(utcDateTime, DateTimeKind.Unspecified) + offset, offset);
                        }
                        else {
                                return new DateTimeOffset(DateTime.SpecifyKind(utcDateTime, DateTimeKind.Unspecified) + destinationTimeZone.BaseUtcOffset, destinationTimeZone.BaseUtcOffset);
                        }
                }

                public static DateTime ConvertTimeBySystemTimeZoneId (DateTime dateTime, string destinationTimeZoneId)
                {
                        return ConvertTime (dateTime, FindSystemTimeZoneById (destinationTimeZoneId));
                }

                public static DateTime ConvertTimeBySystemTimeZoneId (DateTime dateTime, string sourceTimeZoneId, string destinationTimeZoneId)
                {
                        return ConvertTime (dateTime, FindSystemTimeZoneById (sourceTimeZoneId), FindSystemTimeZoneById (destinationTimeZoneId));
                }

                public static DateTimeOffset ConvertTimeBySystemTimeZoneId (DateTimeOffset dateTimeOffset, string destinationTimeZoneId)
                {
                        return ConvertTime (dateTimeOffset, FindSystemTimeZoneById (destinationTimeZoneId));
                }

                private DateTime ConvertTimeFromUtc (DateTime dateTime)
                {
                        if (dateTime.Kind == DateTimeKind.Local)
                                throw new ArgumentException ("Kind property of dateTime is Local");

                        if (this == TimeZoneInfo.Utc)
                                return DateTime.SpecifyKind (dateTime, DateTimeKind.Utc);
                        
                        //FIXME: do not rely on DateTime implementation !
                        if (this == TimeZoneInfo.Local) 
                        {
                                return dateTime.ToLocalTime ();
                        }


                        AdjustmentRule rule = GetApplicableRule (dateTime);
                        if (rule != null && IsDaylightSavingTime (DateTime.SpecifyKind (dateTime, DateTimeKind.Utc)))
                                return DateTime.SpecifyKind (dateTime + BaseUtcOffset + rule.DaylightDelta , DateTimeKind.Unspecified);
                        else
                                return DateTime.SpecifyKind (dateTime + BaseUtcOffset, DateTimeKind.Unspecified);
                }

                public static DateTime ConvertTimeFromUtc (DateTime dateTime, TimeZoneInfo destinationTimeZone)
                {
                        if (destinationTimeZone == null)
                                throw new ArgumentNullException ("destinationTimeZone");

                        return destinationTimeZone.ConvertTimeFromUtc (dateTime);
                }

                public static DateTime ConvertTimeToUtc (DateTime dateTime)
                {
                        if (dateTime.Kind == DateTimeKind.Utc)
                                return dateTime;

                        return ConvertTimeToUtc (dateTime, TimeZoneInfo.Local);
                }

                static internal DateTime ConvertTimeToUtc(DateTime dateTime, TimeZoneInfoOptions flags)
                {
                        return ConvertTimeToUtc (dateTime, TimeZoneInfo.Local, flags);
                }

                public static DateTime ConvertTimeToUtc (DateTime dateTime, TimeZoneInfo sourceTimeZone)
                {
                        return ConvertTimeToUtc (dateTime, sourceTimeZone, TimeZoneInfoOptions.None);
                }

                static DateTime ConvertTimeToUtc (DateTime dateTime, TimeZoneInfo sourceTimeZone, TimeZoneInfoOptions flags)
                {
                        if ((flags & TimeZoneInfoOptions.NoThrowOnInvalidTime) == 0) {
                                if (sourceTimeZone == null)
                                        throw new ArgumentNullException ("sourceTimeZone");

                                if (dateTime.Kind == DateTimeKind.Utc && sourceTimeZone != TimeZoneInfo.Utc)
                                        throw new ArgumentException ("Kind property of dateTime is Utc but the sourceTimeZone does not equal TimeZoneInfo.Utc");

                                if (dateTime.Kind == DateTimeKind.Local && sourceTimeZone != TimeZoneInfo.Local)
                                        throw new ArgumentException ("Kind property of dateTime is Local but the sourceTimeZone does not equal TimeZoneInfo.Local");

                                if (sourceTimeZone.IsInvalidTime (dateTime))
                                        throw new ArgumentException ("dateTime parameter is an invalid time");
                        }

                        if (dateTime.Kind == DateTimeKind.Utc)
                                return dateTime;

                        if (sourceTimeZone.IsAmbiguousTime (dateTime) || !sourceTimeZone.IsDaylightSavingTime (dateTime)) {
                                var ticks = dateTime.Ticks - sourceTimeZone.BaseUtcOffset.Ticks;
                                if (ticks < DateTime.MinValue.Ticks)
                                        ticks = DateTime.MinValue.Ticks;
                                else if (ticks > DateTime.MaxValue.Ticks)
                                        ticks = DateTime.MaxValue.Ticks;

                                return new DateTime (ticks, DateTimeKind.Utc);
                        }
                        
                                AdjustmentRule rule = sourceTimeZone.GetApplicableRule (dateTime);
                                if (rule != null)
                                        return DateTime.SpecifyKind (dateTime - sourceTimeZone.BaseUtcOffset - rule.DaylightDelta, DateTimeKind.Utc);
                                else
                                        return DateTime.SpecifyKind (dateTime - sourceTimeZone.BaseUtcOffset, DateTimeKind.Utc);
                        
                }

                static internal TimeSpan GetDateTimeNowUtcOffsetFromUtc(DateTime time, out Boolean isAmbiguousLocalDst)
                {
                        bool isDaylightSavings;
                        return GetUtcOffsetFromUtc(time, TimeZoneInfo.Local, out isDaylightSavings, out isAmbiguousLocalDst);
                }

                public static TimeZoneInfo CreateCustomTimeZone (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName) 
                {
                        return CreateCustomTimeZone (id, baseUtcOffset, displayName, standardDisplayName, null, null, true);
                }

                public static TimeZoneInfo CreateCustomTimeZone (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules)
                {
                        return CreateCustomTimeZone (id, baseUtcOffset, displayName, standardDisplayName, daylightDisplayName, adjustmentRules, false);
                }

                public static TimeZoneInfo CreateCustomTimeZone ( string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules, bool disableDaylightSavingTime)
                {
                        return new TimeZoneInfo (id, baseUtcOffset, displayName, standardDisplayName, daylightDisplayName, adjustmentRules, disableDaylightSavingTime);
                }

                public override bool Equals (object obj)
                {
                        return Equals (obj as TimeZoneInfo);
                }

                public bool Equals (TimeZoneInfo other)
                {
                        if (other == null)
                                return false;

                        return other.Id == this.Id && HasSameRules (other);
                }

                public static TimeZoneInfo FindSystemTimeZoneById (string id)
                {
                        //FIXME: this method should check for cached values in systemTimeZones
                        if (id == null)
                                throw new ArgumentNullException ("id");
#if !NET_2_1
                        if (TimeZoneKey != null)
                        {
                                RegistryKey key = TimeZoneKey.OpenSubKey (id, false);
                                if (key == null)
                                        throw new TimeZoneNotFoundException ();
                                return FromRegistryKey(id, key);
                        }
#endif
                        // Local requires special logic that already exists in the Local property (bug #326)
                        if (id == "Local")
                                return Local;
#if MONOTOUCH
                        using (Stream stream = GetMonoTouchData (id)) {
                                return BuildFromStream (id, stream);
                        }
#elif MONODROID
                        var timeZoneInfo = AndroidTimeZones.GetTimeZone (id, id);
                        if (timeZoneInfo == null)
                                throw new TimeZoneNotFoundException ();
                        return timeZoneInfo;
#elif LIBC
                        string filepath = Path.Combine (TimeZoneDirectory, id);
                        return FindSystemTimeZoneByFileName (id, filepath);
#else
                        throw new NotImplementedException ();
#endif
                }

#if LIBC
                private static TimeZoneInfo FindSystemTimeZoneByFileName (string id, string filepath)
                {
                        if (!File.Exists (filepath))
                                throw new TimeZoneNotFoundException ();

                        using (FileStream stream = File.OpenRead (filepath)) {
                                return BuildFromStream (id, stream);
                        }
                }
#endif
#if LIBC || MONOTOUCH
                const int BUFFER_SIZE = 16384; //Big enough for any tz file (on Oct 2008, all tz files are under 10k)
                
                private static TimeZoneInfo BuildFromStream (string id, Stream stream) 
                {
                        byte [] buffer = new byte [BUFFER_SIZE];
                        int length = stream.Read (buffer, 0, BUFFER_SIZE);
                        
                        if (!ValidTZFile (buffer, length))
                                throw new InvalidTimeZoneException ("TZ file too big for the buffer");

                        try {
                                return ParseTZBuffer (id, buffer, length);
                        } catch (Exception e) {
                                throw new InvalidTimeZoneException (e.Message);
                        }
                }
#endif

#if !NET_2_1
                private static TimeZoneInfo FromRegistryKey (string id, RegistryKey key)
                {
                        byte [] reg_tzi = (byte []) key.GetValue ("TZI");

                        if (reg_tzi == null)
                                throw new InvalidTimeZoneException ();

                        int bias = BitConverter.ToInt32 (reg_tzi, 0);
                        TimeSpan baseUtcOffset = new TimeSpan (0, -bias, 0);

                        string display_name = (string) key.GetValue ("Display");
                        string standard_name = (string) key.GetValue ("Std");
                        string daylight_name = (string) key.GetValue ("Dlt");

                        List<AdjustmentRule> adjustmentRules = new List<AdjustmentRule> ();

                        RegistryKey dst_key = key.OpenSubKey ("Dynamic DST", false);
                        if (dst_key != null) {
                                int first_year = (int) dst_key.GetValue ("FirstEntry");
                                int last_year = (int) dst_key.GetValue ("LastEntry");
                                int year;

                                for (year=first_year; year<=last_year; year++) {
                                        byte [] dst_tzi = (byte []) dst_key.GetValue (year.ToString ());
                                        if (dst_tzi != null) {
                                                int start_year = year == first_year ? 1 : year;
                                                int end_year = year == last_year ? 9999 : year;
                                                ParseRegTzi(adjustmentRules, start_year, end_year, dst_tzi);
                                        }
                                }
                        }
                        else
                                ParseRegTzi(adjustmentRules, 1, 9999, reg_tzi);

                        return CreateCustomTimeZone (id, baseUtcOffset, display_name, standard_name, daylight_name, ValidateRules (adjustmentRules).ToArray ());
                }

                private static void ParseRegTzi (List<AdjustmentRule> adjustmentRules, int start_year, int end_year, byte [] buffer)
                {
                        //int standard_bias = BitConverter.ToInt32 (buffer, 4); /* not sure how to handle this */
                        int daylight_bias = BitConverter.ToInt32 (buffer, 8);

                        int standard_year = BitConverter.ToInt16 (buffer, 12);
                        int standard_month = BitConverter.ToInt16 (buffer, 14);
                        int standard_dayofweek = BitConverter.ToInt16 (buffer, 16);
                        int standard_day = BitConverter.ToInt16 (buffer, 18);
                        int standard_hour = BitConverter.ToInt16 (buffer, 20);
                        int standard_minute = BitConverter.ToInt16 (buffer, 22);
                        int standard_second = BitConverter.ToInt16 (buffer, 24);
                        int standard_millisecond = BitConverter.ToInt16 (buffer, 26);

                        int daylight_year = BitConverter.ToInt16 (buffer, 28);
                        int daylight_month = BitConverter.ToInt16 (buffer, 30);
                        int daylight_dayofweek = BitConverter.ToInt16 (buffer, 32);
                        int daylight_day = BitConverter.ToInt16 (buffer, 34);
                        int daylight_hour = BitConverter.ToInt16 (buffer, 36);
                        int daylight_minute = BitConverter.ToInt16 (buffer, 38);
                        int daylight_second = BitConverter.ToInt16 (buffer, 40);
                        int daylight_millisecond = BitConverter.ToInt16 (buffer, 42);

                        if (standard_month == 0 || daylight_month == 0)
                                return;

                        DateTime start_date;
                        DateTime start_timeofday = new DateTime (1, 1, 1, daylight_hour, daylight_minute, daylight_second, daylight_millisecond);
                        TransitionTime start_transition_time;

                        if (daylight_year == 0) {
                                start_date = new DateTime (start_year, 1, 1);
                                start_transition_time = TransitionTime.CreateFloatingDateRule (
                                        start_timeofday, daylight_month, daylight_day,
                                        (DayOfWeek) daylight_dayofweek);
                        }
                        else {
                                start_date = new DateTime (daylight_year, daylight_month, daylight_day,
                                        daylight_hour, daylight_minute, daylight_second, daylight_millisecond);
                                start_transition_time = TransitionTime.CreateFixedDateRule (
                                        start_timeofday, daylight_month, daylight_day);
                        }

                        DateTime end_date;
                        DateTime end_timeofday = new DateTime (1, 1, 1, standard_hour, standard_minute, standard_second, standard_millisecond);
                        TransitionTime end_transition_time;

                        if (standard_year == 0) {
                                end_date = new DateTime (end_year, 12, 31);
                                end_transition_time = TransitionTime.CreateFloatingDateRule (
                                        end_timeofday, standard_month, standard_day,
                                        (DayOfWeek) standard_dayofweek);
                        }
                        else {
                                end_date = new DateTime (standard_year, standard_month, standard_day,
                                        standard_hour, standard_minute, standard_second, standard_millisecond);
                                end_transition_time = TransitionTime.CreateFixedDateRule (
                                        end_timeofday, standard_month, standard_day);
                        }

                        TimeSpan daylight_delta = new TimeSpan(0, -daylight_bias, 0);

                        adjustmentRules.Add (AdjustmentRule.CreateAdjustmentRule (
                                start_date, end_date, daylight_delta,
                                start_transition_time, end_transition_time));
                }
#endif

                public AdjustmentRule [] GetAdjustmentRules ()
                {
                        if (!supportsDaylightSavingTime)
                                return new AdjustmentRule [0];
                        else
                                return (AdjustmentRule []) adjustmentRules.Clone ();
                }

                public TimeSpan [] GetAmbiguousTimeOffsets (DateTime dateTime)
                {
                        if (!IsAmbiguousTime (dateTime))
                                throw new ArgumentException ("dateTime is not an ambiguous time");

                        AdjustmentRule rule = GetApplicableRule (dateTime);
                        if (rule != null)
                                return new TimeSpan[] {baseUtcOffset, baseUtcOffset + rule.DaylightDelta};
                        else
                                return new TimeSpan[] {baseUtcOffset, baseUtcOffset};
                }

                public TimeSpan [] GetAmbiguousTimeOffsets (DateTimeOffset dateTimeOffset)
                {
                        if (!IsAmbiguousTime (dateTimeOffset))
                                throw new ArgumentException ("dateTimeOffset is not an ambiguous time");

                        throw new NotImplementedException ();
                }

                public override int GetHashCode ()
                {
                        int hash_code = Id.GetHashCode ();
                        foreach (AdjustmentRule rule in GetAdjustmentRules ())
                                hash_code ^= rule.GetHashCode ();
                        return hash_code;
                }

                void ISerializable.GetObjectData (SerializationInfo info, StreamingContext context)
                {
                        if (info == null)
                                throw new ArgumentNullException ("info");
                        info.AddValue ("Id", id);
                        info.AddValue ("DisplayName", displayName);
                        info.AddValue ("StandardName", standardDisplayName);
                        info.AddValue ("DaylightName", daylightDisplayName);
                        info.AddValue ("BaseUtcOffset", baseUtcOffset);
                        info.AddValue ("AdjustmentRules", adjustmentRules);
                        info.AddValue ("SupportsDaylightSavingTime", SupportsDaylightSavingTime);
                }

                //FIXME: change this to a generic Dictionary and allow caching for FindSystemTimeZoneById
                private static List<TimeZoneInfo> systemTimeZones;
                public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones ()
                {
                        if (systemTimeZones == null) {
                                systemTimeZones = new List<TimeZoneInfo> ();
#if !NET_2_1
                                if (TimeZoneKey != null) {
                                        foreach (string id in TimeZoneKey.GetSubKeyNames ()) {
                                                try {
                                                        systemTimeZones.Add (FindSystemTimeZoneById (id));
                                                } catch {}
                                        }

                                        return new ReadOnlyCollection<TimeZoneInfo> (systemTimeZones);
                                }
#endif
#if MONODROID
                        foreach (string id in AndroidTimeZones.GetAvailableIds ()) {
                                var tz = AndroidTimeZones.GetTimeZone (id, id);
                                if (tz != null)
                                        systemTimeZones.Add (tz);
                        }
#elif MONOTOUCH
                                if (systemTimeZones.Count == 0) {
                                        foreach (string name in GetMonoTouchNames ()) {
                                                using (Stream stream = GetMonoTouchData (name, false)) {
                                                        if (stream == null)
                                                                continue;
                                                        systemTimeZones.Add (BuildFromStream (name, stream));
                                                }
                                        }
                                }
#elif LIBC
                                string[] continents = new string [] {"Africa", "America", "Antarctica", "Arctic", "Asia", "Atlantic", "Brazil", "Canada", "Chile", "Europe", "Indian", "Mexico", "Mideast", "Pacific", "US"};
                                foreach (string continent in continents) {
                                        try {
                                                foreach (string zonepath in Directory.GetFiles (Path.Combine (TimeZoneDirectory, continent))) {
                                                        try {
                                                                string id = String.Format ("{0}/{1}", continent, Path.GetFileName (zonepath));
                                                                systemTimeZones.Add (FindSystemTimeZoneById (id));
                                                        } catch (ArgumentNullException) {
                                                        } catch (TimeZoneNotFoundException) {
                                                        } catch (InvalidTimeZoneException) {
                                                        } catch (Exception) {
                                                                throw;
                                                        }
                                                }
                                        } catch {}
                                }
#else
                                throw new NotImplementedException ("This method is not implemented for this platform");
#endif
                        }
                        return new ReadOnlyCollection<TimeZoneInfo> (systemTimeZones);
                }

                public TimeSpan GetUtcOffset (DateTime dateTime)
                {
                        bool isDST;
                        return GetUtcOffset (dateTime, out isDST);
                }

                public TimeSpan GetUtcOffset (DateTimeOffset dateTimeOffset)
                {
                        throw new NotImplementedException ();
                }

                private TimeSpan GetUtcOffset (DateTime dateTime, out bool isDST)
                {
                        isDST = false;

                        TimeZoneInfo tz = this;
                        if (dateTime.Kind == DateTimeKind.Utc)
                                tz = TimeZoneInfo.Utc;

                        if (dateTime.Kind == DateTimeKind.Local)
                                tz = TimeZoneInfo.Local;

                        bool isTzDst;
                        var tzOffset = GetUtcOffset (dateTime, tz, out isTzDst);

                        if (tz == this) {
                                isDST = isTzDst;
                                return tzOffset;
                        }

                        var utcTicks = dateTime.Ticks - tzOffset.Ticks;
                        if (utcTicks < 0 || utcTicks > DateTime.MaxValue.Ticks)
                                return BaseUtcOffset;

                        var utcDateTime = new DateTime (utcTicks, DateTimeKind.Utc);

                        return GetUtcOffset (utcDateTime, this, out isDST);
                }

                private static TimeSpan GetUtcOffset (DateTime dateTime, TimeZoneInfo tz, out bool isDST)
                {
                        if (dateTime.Kind == DateTimeKind.Local && tz != TimeZoneInfo.Local)
                                throw new Exception ();

                        isDST = false;

                        if (tz == TimeZoneInfo.Utc)
                                return TimeSpan.Zero;

                        TimeSpan offset;
                        if (tz.TryGetTransitionOffset(dateTime, out offset, out isDST))
                                return offset;

                        if (dateTime.Kind == DateTimeKind.Utc) {
                                var utcRule = tz.GetApplicableRule (dateTime);
                                if (utcRule != null && tz.IsInDST (utcRule, dateTime)) {
                                        isDST = true;
                                        return tz.BaseUtcOffset + utcRule.DaylightDelta;
                                }

                                return tz.BaseUtcOffset;
                        }

                        var stdTicks = dateTime.Ticks - tz.BaseUtcOffset.Ticks;
                        if (stdTicks < 0 || stdTicks > DateTime.MaxValue.Ticks)
                                return tz.BaseUtcOffset;

                        var stdUtcDateTime = new DateTime (stdTicks, DateTimeKind.Utc);
                        var tzRule = tz.GetApplicableRule (stdUtcDateTime);

                        DateTime dstUtcDateTime = DateTime.MinValue;
                        if (tzRule != null) {
                                var dstTicks = stdUtcDateTime.Ticks - tzRule.DaylightDelta.Ticks;
                                if (dstTicks < 0 || dstTicks > DateTime.MaxValue.Ticks)
                                        return tz.BaseUtcOffset;

                                dstUtcDateTime = new DateTime (dstTicks, DateTimeKind.Utc);
                        }

                        if (tzRule != null && tz.IsInDST (tzRule, stdUtcDateTime) && tz.IsInDST (tzRule, dstUtcDateTime)) {
                                isDST = true;
                                return tz.BaseUtcOffset + tzRule.DaylightDelta;
                        }

                        return tz.BaseUtcOffset;
                }

                public bool HasSameRules (TimeZoneInfo other)
                {
                        if (other == null)
                                throw new ArgumentNullException ("other");

                        if ((this.adjustmentRules == null) != (other.adjustmentRules == null))
                                return false;

                        if (this.adjustmentRules == null)
                                return true;

                        if (this.BaseUtcOffset != other.BaseUtcOffset)
                                return false;

                        if (this.adjustmentRules.Length != other.adjustmentRules.Length)
                                return false;

                        for (int i = 0; i < adjustmentRules.Length; i++) {
                                if (! (this.adjustmentRules [i]).Equals (other.adjustmentRules [i]))
                                        return false;
                        }
                        
                        return true;
                }

                public bool IsAmbiguousTime (DateTime dateTime)
                {
                        if (dateTime.Kind == DateTimeKind.Local && IsInvalidTime (dateTime))
                                throw new ArgumentException ("Kind is Local and time is Invalid");

                        if (this == TimeZoneInfo.Utc)
                                return false;
                        
                        if (dateTime.Kind == DateTimeKind.Utc)
                                dateTime = ConvertTimeFromUtc (dateTime);

                        if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local)
                                dateTime = ConvertTime (dateTime, TimeZoneInfo.Local, this);

                        AdjustmentRule rule = GetApplicableRule (dateTime);
                        if (rule != null) {
                                DateTime tpoint = TransitionPoint (rule.DaylightTransitionEnd, dateTime.Year);
                                if (dateTime > tpoint - rule.DaylightDelta  && dateTime <= tpoint)
                                        return true;
                        }
                                
                        return false;
                }

                public bool IsAmbiguousTime (DateTimeOffset dateTimeOffset)
                {
                        throw new NotImplementedException ();
                }

                private bool IsInDST (AdjustmentRule rule, DateTime dateTime)
                {
                        // Check whether we're in the dateTime year's DST period
                        if (IsInDSTForYear (rule, dateTime, dateTime.Year))
                                return true;

                        // We might be in the dateTime previous year's DST period
                        return IsInDSTForYear (rule, dateTime, dateTime.Year - 1);
                }

                bool IsInDSTForYear (AdjustmentRule rule, DateTime dateTime, int year)
                {
                        DateTime DST_start = TransitionPoint (rule.DaylightTransitionStart, year);
                        DateTime DST_end = TransitionPoint (rule.DaylightTransitionEnd, year + ((rule.DaylightTransitionStart.Month < rule.DaylightTransitionEnd.Month) ? 0 : 1));
                        if (dateTime.Kind == DateTimeKind.Utc) {
                                DST_start -= BaseUtcOffset;
                                DST_end -= (BaseUtcOffset + rule.DaylightDelta);
                        }

                        return (dateTime >= DST_start && dateTime < DST_end);
                }
                
                public bool IsDaylightSavingTime (DateTime dateTime)
                {
                        if (dateTime.Kind == DateTimeKind.Local && IsInvalidTime (dateTime))
                                throw new ArgumentException ("dateTime is invalid and Kind is Local");

                        if (this == TimeZoneInfo.Utc)
                                return false;
                        
                        if (!SupportsDaylightSavingTime)
                                return false;

                        bool isDst;
                        GetUtcOffset (dateTime, out isDst);

                        return isDst;
                }

                internal bool IsDaylightSavingTime (DateTime dateTime, TimeZoneInfoOptions flags)
                {
                        return IsDaylightSavingTime (dateTime);
                }

                public bool IsDaylightSavingTime (DateTimeOffset dateTimeOffset)
                {
                        throw new NotImplementedException ();
                }

                void IDeserializationCallback.OnDeserialization (object sender)
                {
                        try {
                                        TimeZoneInfo.Validate (id, baseUtcOffset, adjustmentRules);
                                } catch (ArgumentException ex) {
                                        throw new SerializationException ("invalid serialization data", ex);
                                }
                }

                private static void Validate (string id, TimeSpan baseUtcOffset, AdjustmentRule [] adjustmentRules)
                {
                        if (id == null)
                                throw new ArgumentNullException ("id");

                        if (id == String.Empty)
                                throw new ArgumentException ("id parameter is an empty string");

                        if (baseUtcOffset.Ticks % TimeSpan.TicksPerMinute != 0)
                                throw new ArgumentException ("baseUtcOffset parameter does not represent a whole number of minutes");

                        if (baseUtcOffset > new TimeSpan (14, 0, 0) || baseUtcOffset < new TimeSpan (-14, 0, 0))
                                throw new ArgumentOutOfRangeException ("baseUtcOffset parameter is greater than 14 hours or less than -14 hours");

#if STRICT
                        if (id.Length > 32)
                                throw new ArgumentException ("id parameter shouldn't be longer than 32 characters");
#endif

                        if (adjustmentRules != null && adjustmentRules.Length != 0) {
                                AdjustmentRule prev = null;
                                foreach (AdjustmentRule current in adjustmentRules) {
                                        if (current == null)
                                                throw new InvalidTimeZoneException ("one or more elements in adjustmentRules are null");

                                        if ((baseUtcOffset + current.DaylightDelta < new TimeSpan (-14, 0, 0)) ||
                                                        (baseUtcOffset + current.DaylightDelta > new TimeSpan (14, 0, 0)))
                                                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;");

                                        if (prev != null && prev.DateStart > current.DateStart)
                                                throw new InvalidTimeZoneException ("adjustment rules specified in adjustmentRules parameter are not in chronological order");
                                        
                                        if (prev != null && prev.DateEnd > current.DateStart)
                                                throw new InvalidTimeZoneException ("some adjustment rules in the adjustmentRules parameter overlap");

                                        if (prev != null && prev.DateEnd == current.DateStart)
                                                throw new InvalidTimeZoneException ("a date can have multiple adjustment rules applied to it");

                                        prev = current;
                                }
                        }
                }
                
                public override string ToString ()
                {
                        return DisplayName;
                }

                private TimeZoneInfo (SerializationInfo info, StreamingContext context)
                {
                        if (info == null)
                                throw new ArgumentNullException ("info");
                        id = (string) info.GetValue ("Id", typeof (string));
                        displayName = (string) info.GetValue ("DisplayName", typeof (string));
                        standardDisplayName = (string) info.GetValue ("StandardName", typeof (string));
                        daylightDisplayName = (string) info.GetValue ("DaylightName", typeof (string));
                        baseUtcOffset = (TimeSpan) info.GetValue ("BaseUtcOffset", typeof (TimeSpan));
                        adjustmentRules = (TimeZoneInfo.AdjustmentRule []) info.GetValue ("AdjustmentRules", typeof (TimeZoneInfo.AdjustmentRule []));
                        supportsDaylightSavingTime = (bool) info.GetValue ("SupportsDaylightSavingTime", typeof (bool));
                }

                private TimeZoneInfo (string id, TimeSpan baseUtcOffset, string displayName, string standardDisplayName, string daylightDisplayName, TimeZoneInfo.AdjustmentRule [] adjustmentRules, bool disableDaylightSavingTime)
                {
                        if (id == null)
                                throw new ArgumentNullException ("id");

                        if (id == String.Empty)
                                throw new ArgumentException ("id parameter is an empty string");

                        if (baseUtcOffset.Ticks % TimeSpan.TicksPerMinute != 0)
                                throw new ArgumentException ("baseUtcOffset parameter does not represent a whole number of minutes");

                        if (baseUtcOffset > new TimeSpan (14, 0, 0) || baseUtcOffset < new TimeSpan (-14, 0, 0))
                                throw new ArgumentOutOfRangeException ("baseUtcOffset parameter is greater than 14 hours or less than -14 hours");

#if STRICT
                        if (id.Length > 32)
                                throw new ArgumentException ("id parameter shouldn't be longer than 32 characters");
#endif

                        bool supportsDaylightSavingTime = !disableDaylightSavingTime;

                        if (adjustmentRules != null && adjustmentRules.Length != 0) {
                                AdjustmentRule prev = null;
                                foreach (AdjustmentRule current in adjustmentRules) {
                                        if (current == null)
                                                throw new InvalidTimeZoneException ("one or more elements in adjustmentRules are null");

                                        if ((baseUtcOffset + current.DaylightDelta < new TimeSpan (-14, 0, 0)) ||
                                                        (baseUtcOffset + current.DaylightDelta > new TimeSpan (14, 0, 0)))
                                                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;");

                                        if (prev != null && prev.DateStart > current.DateStart)
                                                throw new InvalidTimeZoneException ("adjustment rules specified in adjustmentRules parameter are not in chronological order");
                                        
                                        if (prev != null && prev.DateEnd > current.DateStart)
                                                throw new InvalidTimeZoneException ("some adjustment rules in the adjustmentRules parameter overlap");

                                        if (prev != null && prev.DateEnd == current.DateStart)
                                                throw new InvalidTimeZoneException ("a date can have multiple adjustment rules applied to it");

                                        prev = current;
                                }
                        } else {
                                supportsDaylightSavingTime = false;
                        }
                        
                        this.id = id;
                        this.baseUtcOffset = baseUtcOffset;
                        this.displayName = displayName ?? id;
                        this.standardDisplayName = standardDisplayName ?? id;
                        this.daylightDisplayName = daylightDisplayName;
                        this.supportsDaylightSavingTime = supportsDaylightSavingTime;
                        this.adjustmentRules = adjustmentRules;
                }

                private AdjustmentRule GetApplicableRule (DateTime dateTime)
                {
                        //Transitions are always in standard time
                        DateTime date = dateTime;

                        if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local)
                                date = date.ToUniversalTime () + BaseUtcOffset;
                        else if (dateTime.Kind == DateTimeKind.Utc && this != TimeZoneInfo.Utc)
                                date = date + BaseUtcOffset;

                        // get the date component of the datetime
                        date = date.Date;

                        if (adjustmentRules != null) {
                                foreach (AdjustmentRule rule in adjustmentRules) {
                                        if (rule.DateStart > date)
                                                return null;
                                        if (rule.DateEnd < date)
                                                continue;
                                        return rule;
                                }
                        }
                        return null;
                }

                private bool TryGetTransitionOffset (DateTime dateTime, out TimeSpan offset,out bool isDst)
                {
                        offset = BaseUtcOffset;
                        isDst = false;

                        if (transitions == null)
                                return false;

                        //Transitions are always in standard time
                        DateTime date = dateTime;

                        if (dateTime.Kind == DateTimeKind.Local && this != TimeZoneInfo.Local)
                                date = date.ToUniversalTime () + BaseUtcOffset;

                        if (dateTime.Kind == DateTimeKind.Utc && this != TimeZoneInfo.Utc)
                                date = date + BaseUtcOffset;

                        for (var i =  transitions.Count - 1; i >= 0; i--) {
                                var pair = transitions [i];
                                DateTime ttime = pair.Key;
                                TimeType ttype = pair.Value;

                                if (ttime > date)
                                        continue;

                                offset =  new TimeSpan (0, 0, ttype.Offset);
                                isDst = ttype.IsDst;

                                return true;
                        }

                        return false;
                }

                private static DateTime TransitionPoint (TransitionTime transition, int year)
                {
                        if (transition.IsFixedDateRule)
                                return new DateTime (year, transition.Month, transition.Day) + transition.TimeOfDay.TimeOfDay;

                        DayOfWeek first = (new DateTime (year, transition.Month, 1)).DayOfWeek;
                        int day = 1 + (transition.Week - 1) * 7 + (transition.DayOfWeek - first + 7) % 7;
                        if (day >  DateTime.DaysInMonth (year, transition.Month))
                                day -= 7;
                        if (day < 1)
                                day += 7;
                        return new DateTime (year, transition.Month, day) + transition.TimeOfDay.TimeOfDay;
                }

                static List<AdjustmentRule> ValidateRules (List<AdjustmentRule> adjustmentRules)
                {
                        AdjustmentRule prev = null;
                        foreach (AdjustmentRule current in adjustmentRules.ToArray ()) {
                                if (prev != null && prev.DateEnd > current.DateStart) {
                                        adjustmentRules.Remove (current);
                                }
                                prev = current;
                        }
                        return adjustmentRules;
                }

#if LIBC || MONODROID
                private static bool ValidTZFile (byte [] buffer, int length)
                {
                        StringBuilder magic = new StringBuilder ();

                        for (int i = 0; i < 4; i++)
                                magic.Append ((char)buffer [i]);
                        
                        if (magic.ToString () != "TZif")
                                return false;

                        if (length >= BUFFER_SIZE)
                                return false;

                        return true;
                }

                static int SwapInt32 (int i)
                {
                        return (((i >> 24) & 0xff)
                                | ((i >> 8) & 0xff00)
                                | ((i << 8) & 0xff0000)
                                | ((i << 24)));
                }

                static int ReadBigEndianInt32 (byte [] buffer, int start)
                {
                        int i = BitConverter.ToInt32 (buffer, start);
                        if (!BitConverter.IsLittleEndian)
                                return i;

                        return SwapInt32 (i);
                }

                private static TimeZoneInfo ParseTZBuffer (string id, byte [] buffer, int length)
                {
                        //Reading the header. 4 bytes for magic, 16 are reserved
                        int ttisgmtcnt = ReadBigEndianInt32 (buffer, 20);
                        int ttisstdcnt = ReadBigEndianInt32 (buffer, 24);
                        int leapcnt = ReadBigEndianInt32 (buffer, 28);
                        int timecnt = ReadBigEndianInt32 (buffer, 32);
                        int typecnt = ReadBigEndianInt32 (buffer, 36);
                        int charcnt = ReadBigEndianInt32 (buffer, 40);

                        if (length < 44 + timecnt * 5 + typecnt * 6 + charcnt + leapcnt * 8 + ttisstdcnt + ttisgmtcnt)
                                throw new InvalidTimeZoneException ();

                        Dictionary<int, string> abbreviations = ParseAbbreviations (buffer, 44 + 4 * timecnt + timecnt + 6 * typecnt, charcnt);
                        Dictionary<int, TimeType> time_types = ParseTimesTypes (buffer, 44 + 4 * timecnt + timecnt, typecnt, abbreviations);
                        List<KeyValuePair<DateTime, TimeType>> transitions = ParseTransitions (buffer, 44, timecnt, time_types);

                        if (time_types.Count == 0)
                                throw new InvalidTimeZoneException ();

                        if (time_types.Count == 1 && ((TimeType)time_types[0]).IsDst)
                                throw new InvalidTimeZoneException ();

                        TimeSpan baseUtcOffset = new TimeSpan (0);
                        TimeSpan dstDelta = new TimeSpan (0);
                        string standardDisplayName = null;
                        string daylightDisplayName = null;
                        bool dst_observed = false;
                        DateTime dst_start = DateTime.MinValue;
                        List<AdjustmentRule> adjustmentRules = new List<AdjustmentRule> ();
                        bool storeTransition = false;

                        for (int i = 0; i < transitions.Count; i++) {
                                var pair = transitions [i];
                                DateTime ttime = pair.Key;
                                TimeType ttype = pair.Value;
                                if (!ttype.IsDst) {
                                        if (standardDisplayName != ttype.Name)
                                                standardDisplayName = ttype.Name;
                                        if (baseUtcOffset.TotalSeconds != ttype.Offset) {
                                                baseUtcOffset = new TimeSpan (0, 0, ttype.Offset);
                                                if (adjustmentRules.Count > 0) // We ignore AdjustmentRules but store transitions.
                                                        storeTransition = true;
                                                adjustmentRules = new List<AdjustmentRule> ();
                                                dst_observed = false;
                                        }
                                        if (dst_observed) {
                                                //FIXME: check additional fields for this:
                                                //most of the transitions are expressed in GMT 
                                                dst_start += baseUtcOffset;
                                                DateTime dst_end = ttime + baseUtcOffset + dstDelta;

                                                //some weird timezone (America/Phoenix) have end dates on Jan 1st
                                                if (dst_end.Date == new DateTime (dst_end.Year, 1, 1) && dst_end.Year > dst_start.Year)
                                                        dst_end -= new TimeSpan (24, 0, 0);

                                                DateTime dateStart, dateEnd;
                                                if (dst_start.Month < 7)
                                                        dateStart = new DateTime (dst_start.Year, 1, 1);
                                                else
                                                        dateStart = new DateTime (dst_start.Year, 7, 1);

                                                if (dst_end.Month >= 7)
                                                        dateEnd = new DateTime (dst_end.Year, 12, 31);
                                                else
                                                        dateEnd = new DateTime (dst_end.Year, 6, 30);

                                                
                                                TransitionTime transition_start = TransitionTime.CreateFixedDateRule (new DateTime (1, 1, 1) + dst_start.TimeOfDay, dst_start.Month, dst_start.Day);
                                                TransitionTime transition_end = TransitionTime.CreateFixedDateRule (new DateTime (1, 1, 1) + dst_end.TimeOfDay, dst_end.Month, dst_end.Day);
                                                if  (transition_start != transition_end) //y, that happened in Argentina in 1943-1946
                                                        adjustmentRules.Add (AdjustmentRule.CreateAdjustmentRule (dateStart, dateEnd, dstDelta, transition_start, transition_end));
                                        }
                                        dst_observed = false;
                                } else {
                                        if (daylightDisplayName != ttype.Name)
                                                daylightDisplayName = ttype.Name;
                                        if (dstDelta.TotalSeconds != ttype.Offset - baseUtcOffset.TotalSeconds)
                                                dstDelta = new TimeSpan(0, 0, ttype.Offset) - baseUtcOffset;

                                        dst_start = ttime;
                                        dst_observed = true;
                                }
                        }

                        TimeZoneInfo tz;
                        if (adjustmentRules.Count == 0 && !storeTransition) {
                                TimeType t = (TimeType)time_types [0];
                                if (standardDisplayName == null) {
                                        standardDisplayName = t.Name;
                                        baseUtcOffset = new TimeSpan (0, 0, t.Offset);
                                }
                                tz = CreateCustomTimeZone (id, baseUtcOffset, id, standardDisplayName);
                        } else {
                                tz = CreateCustomTimeZone (id, baseUtcOffset, id, standardDisplayName, daylightDisplayName, ValidateRules (adjustmentRules).ToArray ());
                        }

                        if (storeTransition)
                                tz.transitions = transitions;

                        return tz;
                }

                static Dictionary<int, string> ParseAbbreviations (byte [] buffer, int index, int count)
                {
                        var abbrevs = new Dictionary<int, string> ();
                        int abbrev_index = 0;
                        var sb = new StringBuilder ();
                        for (int i = 0; i < count; i++) {
                                char c = (char) buffer [index + i];
                                if (c != '\0')
                                        sb.Append (c);
                                else {
                                        abbrevs.Add (abbrev_index, sb.ToString ());
                                        //Adding all the substrings too, as it seems to be used, at least for Africa/Windhoek
                                        for (int j = 1; j < sb.Length; j++)
                                                abbrevs.Add (abbrev_index + j, sb.ToString (j, sb.Length - j));
                                        abbrev_index = i + 1;
                                        sb = new StringBuilder ();
                                }
                        }
                        return abbrevs;
                }

                static Dictionary<int, TimeType> ParseTimesTypes (byte [] buffer, int index, int count, Dictionary<int, string> abbreviations)
                {
                        var types = new Dictionary<int, TimeType> (count);
                        for (int i = 0; i < count; i++) {
                                int offset = ReadBigEndianInt32 (buffer, index + 6 * i);
                                byte is_dst = buffer [index + 6 * i + 4];
                                byte abbrev = buffer [index + 6 * i + 5];
                                types.Add (i, new TimeType (offset, (is_dst != 0), abbreviations [(int)abbrev]));
                        }
                        return types;
                }

                static List<KeyValuePair<DateTime, TimeType>> ParseTransitions (byte [] buffer, int index, int count, Dictionary<int, TimeType> time_types)
                {
                        var list = new List<KeyValuePair<DateTime, TimeType>> (count);
                        for (int i = 0; i < count; i++) {
                                int unixtime = ReadBigEndianInt32 (buffer, index + 4 * i);
                                DateTime ttime = DateTimeFromUnixTime (unixtime);
                                byte ttype = buffer [index + 4 * count + i];
                                list.Add (new KeyValuePair<DateTime, TimeType> (ttime, time_types [(int)ttype]));
                        }
                        return list;
                }

                static DateTime DateTimeFromUnixTime (long unix_time)
                {
                        DateTime date_time = new DateTime (1970, 1, 1);
                        return date_time.AddSeconds (unix_time);
                }

#region reference sources
        // Shortcut for TimeZoneInfo.Local.GetUtcOffset
        internal static TimeSpan GetLocalUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
        {
            bool dst;
            return Local.GetUtcOffset (dateTime, out dst);
        }

        internal TimeSpan GetUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
        {
            bool dst;
            return GetUtcOffset (dateTime, out dst);
        }

        // used by GetUtcOffsetFromUtc (DateTime.Now, DateTime.ToLocalTime) for max/min whole-day range checks
        private static DateTime s_maxDateOnly = new DateTime(9999, 12, 31);
        private static DateTime s_minDateOnly = new DateTime(1, 1, 2);

        static internal TimeSpan GetUtcOffsetFromUtc (DateTime time, TimeZoneInfo zone, out Boolean isDaylightSavings, out Boolean isAmbiguousLocalDst)
        {
            isDaylightSavings = false;
            isAmbiguousLocalDst = false;
            TimeSpan baseOffset = zone.BaseUtcOffset;
            Int32 year;
            AdjustmentRule rule;

            if (time > s_maxDateOnly) {
                rule = zone.GetAdjustmentRuleForTime(DateTime.MaxValue);
                year = 9999;
            }
            else if (time < s_minDateOnly) {
                rule = zone.GetAdjustmentRuleForTime(DateTime.MinValue);
                year = 1;
            }
            else {
                DateTime targetTime = time + baseOffset;
                year = time.Year;
                rule = zone.GetAdjustmentRuleForTime(targetTime);
            }

            if (rule != null) {
                isDaylightSavings = GetIsDaylightSavingsFromUtc(time, year, zone.baseUtcOffset, rule, out isAmbiguousLocalDst);
                baseOffset += (isDaylightSavings ? rule.DaylightDelta : TimeSpan.Zero /* */);
            }

            return baseOffset;
        }

        // assumes dateTime is in the current time zone's time
        private AdjustmentRule GetAdjustmentRuleForTime(DateTime dateTime) {
            if (adjustmentRules == null || adjustmentRules.Length == 0) {
                return null;
            }

#if WINXP_AND_WIN2K3_SUPPORT
            // On pre-Vista versions of Windows if you run "cmd /c date" or "cmd /c time" to update the system time
            // the operating system doesn't pick up the correct time zone adjustment rule (it stays on the currently loaded rule).
            // We need to use the OS API data in this scenario instead of the loaded adjustment rules from the registry for
            // consistency.  Otherwise DateTime.Now might not match the time displayed in the system tray.              
            if (!Environment.IsWindowsVistaOrAbove && s_cachedData.GetCorrespondingKind(this) == DateTimeKind.Local) {
                return s_cachedData.GetOneYearLocalFromLocal(dateTime.Year).rule;
            }
#endif
            // Only check the whole-date portion of the dateTime -
            // This is because the AdjustmentRule DateStart & DateEnd are stored as
            // Date-only values {4/2/2006 - 10/28/2006} but actually represent the
            // time span {4/2/2006@00:00:00.00000 - 10/28/2006@23:59:59.99999}
            DateTime date = dateTime.Date;

            for (int i = 0; i < adjustmentRules.Length; i++) {
                if (adjustmentRules[i].DateStart <= date && adjustmentRules[i].DateEnd >= date) {
                    return adjustmentRules[i];
                }
            }

            return null;
        }

        //
        // GetIsDaylightSavingsFromUtc -
        //
        // Helper function that checks if a given dateTime is in Daylight Saving Time (DST)
        // This function assumes the dateTime is in UTC and AdjustmentRule is in a different time zone
        //
        static private Boolean GetIsDaylightSavingsFromUtc(DateTime time, Int32 Year, TimeSpan utc, AdjustmentRule rule, out Boolean isAmbiguousLocalDst) {
            isAmbiguousLocalDst = false;

            if (rule == null) {
                return false;
            }

            // Get the daylight changes for the year of the specified time.
            TimeSpan offset = utc; /* */
            DaylightTime daylightTime = GetDaylightTime(Year, rule);

            // The start and end times represent the range of universal times that are in DST for that year.                
            // Within that there is an ambiguous hour, usually right at the end, but at the beginning in
            // the unusual case of a negative daylight savings delta.
            DateTime startTime = daylightTime.Start - offset;
            DateTime endTime = daylightTime.End - offset - rule.DaylightDelta; /* */
            DateTime ambiguousStart;
            DateTime ambiguousEnd;
            if (daylightTime.Delta.Ticks > 0) {
                ambiguousStart = endTime - daylightTime.Delta;
                ambiguousEnd = endTime;
            } else {
                ambiguousStart = startTime;
                ambiguousEnd = startTime - daylightTime.Delta;
            }

            Boolean isDst = CheckIsDst(startTime, time, endTime);

            // See if the resulting local time becomes ambiguous. This must be captured here or the
            // DateTime will not be able to round-trip back to UTC accurately.
            if (isDst) {
                isAmbiguousLocalDst = (time >= ambiguousStart && time < ambiguousEnd);

                if (!isAmbiguousLocalDst && ambiguousStart.Year != ambiguousEnd.Year) {
                    // there exists an extreme corner case where the start or end period is on a year boundary and
                    // because of this the comparison above might have been performed for a year-early or a year-later
                    // than it should have been.
                    DateTime ambiguousStartModified;
                    DateTime ambiguousEndModified;
                    try {
                        ambiguousStartModified = ambiguousStart.AddYears(1);
                        ambiguousEndModified   = ambiguousEnd.AddYears(1);
                        isAmbiguousLocalDst = (time >= ambiguousStart && time < ambiguousEnd); 
                    }
                    catch (ArgumentOutOfRangeException) {}

                    if (!isAmbiguousLocalDst) {
                        try {
                            ambiguousStartModified = ambiguousStart.AddYears(-1);
                            ambiguousEndModified   = ambiguousEnd.AddYears(-1);
                            isAmbiguousLocalDst = (time >= ambiguousStart && time < ambiguousEnd);
                        }
                        catch (ArgumentOutOfRangeException) {}
                    }

                }
            }

            return isDst;
        }


        static private Boolean CheckIsDst(DateTime startTime, DateTime time, DateTime endTime) {
            Boolean isDst;

            int startTimeYear = startTime.Year;
            int endTimeYear = endTime.Year;

            if (startTimeYear != endTimeYear) {
                endTime = endTime.AddYears(startTimeYear - endTimeYear);
            }

            int timeYear = time.Year;

            if (startTimeYear != timeYear) {
                time = time.AddYears(startTimeYear - timeYear);
            }

            if (startTime > endTime) {
                // In southern hemisphere, the daylight saving time starts later in the year, and ends in the beginning of next year.
                // Note, the summer in the southern hemisphere begins late in the year.
                isDst = (time < endTime || time >= startTime);
            }
            else {
                // In northern hemisphere, the daylight saving time starts in the middle of the year.
                isDst = (time >= startTime && time < endTime);
            }
            return isDst;
        }

        //
        // GetDaylightTime -
        //
        // Helper function that returns a DaylightTime from a year and AdjustmentRule
        //
        static private DaylightTime GetDaylightTime(Int32 year, AdjustmentRule rule) {
            TimeSpan delta = rule.DaylightDelta;
            DateTime startTime = TransitionTimeToDateTime(year, rule.DaylightTransitionStart);
            DateTime endTime = TransitionTimeToDateTime(year, rule.DaylightTransitionEnd);
            return new DaylightTime(startTime, endTime, delta);
        }

        //
        // TransitionTimeToDateTime -
        //
        // Helper function that converts a year and TransitionTime into a DateTime
        //
        static private DateTime TransitionTimeToDateTime(Int32 year, TransitionTime transitionTime) {
            DateTime value;
            DateTime timeOfDay = transitionTime.TimeOfDay;

            if (transitionTime.IsFixedDateRule) {
                // create a DateTime from the passed in year and the properties on the transitionTime

                // if the day is out of range for the month then use the last day of the month
                Int32 day = DateTime.DaysInMonth(year, transitionTime.Month);

                value = new DateTime(year, transitionTime.Month, (day < transitionTime.Day) ? day : transitionTime.Day, 
                            timeOfDay.Hour, timeOfDay.Minute, timeOfDay.Second, timeOfDay.Millisecond);
            }
            else {
                if (transitionTime.Week <= 4) {
                    //
                    // Get the (transitionTime.Week)th Sunday.
                    //
                    value = new DateTime(year, transitionTime.Month, 1,
                            timeOfDay.Hour, timeOfDay.Minute, timeOfDay.Second, timeOfDay.Millisecond);

                    int dayOfWeek = (int)value.DayOfWeek;
                    int delta = (int)transitionTime.DayOfWeek - dayOfWeek;
                    if (delta < 0) {
                        delta += 7;
                    }
                    delta += 7 * (transitionTime.Week - 1);

                    if (delta > 0) {
                        value = value.AddDays(delta);
                    }
                }
                else {
                    //
                    // If TransitionWeek is greater than 4, we will get the last week.
                    //
                    Int32 daysInMonth = DateTime.DaysInMonth(year, transitionTime.Month);
                    value = new DateTime(year, transitionTime.Month, daysInMonth,
                            timeOfDay.Hour, timeOfDay.Minute, timeOfDay.Second, timeOfDay.Millisecond);

                    // This is the day of week for the last day of the month.
                    int dayOfWeek = (int)value.DayOfWeek;
                    int delta = dayOfWeek - (int)transitionTime.DayOfWeek;
                    if (delta < 0) {
                        delta += 7;
                    }

                    if (delta > 0) {
                        value = value.AddDays(-delta);
                    }
                }
            }
            return value;
        }

        //
        // IsInvalidTime -
        //
        // returns true when dateTime falls into a "hole in time".
        //
        public Boolean IsInvalidTime(DateTime dateTime) {
            Boolean isInvalid = false;
          
            if ( (dateTime.Kind == DateTimeKind.Unspecified)
            ||   (dateTime.Kind == DateTimeKind.Local && this == Local) ) {

                // only check Unspecified and (Local when this TimeZoneInfo instance is Local)
                AdjustmentRule rule = GetAdjustmentRuleForTime(dateTime);


                if (rule != null) {
                    DaylightTime daylightTime = GetDaylightTime(dateTime.Year, rule);
                    isInvalid = GetIsInvalidTime(dateTime, rule, daylightTime);
                }
                else {
                    isInvalid = false;
                }
            }

            return isInvalid;
        }

        //
        // GetIsInvalidTime -
        //
        // Helper function that checks if a given DateTime is in an invalid time ("time hole")
        // A "time hole" occurs at a DST transition point when time jumps forward;
        // For example, in Pacific Standard Time on Sunday, April 2, 2006 time jumps from
        // 1:59:59.9999999 to 3AM.  The time range 2AM to 2:59:59.9999999AM is the "time hole".
        // A "time hole" is not limited to only occurring at the start of DST, and may occur at
        // the end of DST as well.
        //
        static private Boolean GetIsInvalidTime(DateTime time, AdjustmentRule rule, DaylightTime daylightTime) {
            Boolean isInvalid = false;
            if (rule == null || rule.DaylightDelta == TimeSpan.Zero) {
                return isInvalid;
            }

            DateTime startInvalidTime;
            DateTime endInvalidTime;

            // if at DST start we transition forward in time then there is an ambiguous time range at the DST end
            if (rule.DaylightDelta < TimeSpan.Zero) {
                startInvalidTime = daylightTime.End;
                endInvalidTime = daylightTime.End - rule.DaylightDelta; /* */
            }
            else {
                startInvalidTime = daylightTime.Start;
                endInvalidTime = daylightTime.Start + rule.DaylightDelta; /* */
            }

            isInvalid = (time >= startInvalidTime && time < endInvalidTime);

            if (!isInvalid && startInvalidTime.Year != endInvalidTime.Year) {
                // there exists an extreme corner case where the start or end period is on a year boundary and
                // because of this the comparison above might have been performed for a year-early or a year-later
                // than it should have been.
                DateTime startModifiedInvalidTime;
                DateTime endModifiedInvalidTime;
                try {
                    startModifiedInvalidTime = startInvalidTime.AddYears(1);
                    endModifiedInvalidTime   = endInvalidTime.AddYears(1);
                    isInvalid = (time >= startModifiedInvalidTime && time < endModifiedInvalidTime);
                }
                catch (ArgumentOutOfRangeException) {}

                if (!isInvalid) {
                    try {
                        startModifiedInvalidTime = startInvalidTime.AddYears(-1);
                        endModifiedInvalidTime  = endInvalidTime.AddYears(-1);
                        isInvalid = (time >= startModifiedInvalidTime && time < endModifiedInvalidTime);
                    }
                    catch (ArgumentOutOfRangeException) {}
                }
            }
            return isInvalid;
        } 
#endregion
        }

        struct TimeType {
                public readonly int Offset;
                public readonly bool IsDst;
                public string Name;

                public TimeType (int offset, bool is_dst, string abbrev)
                {
                        this.Offset = offset;
                        this.IsDst = is_dst;
                        this.Name = abbrev;
                }

                public override string ToString ()
                {
                        return "offset: " + Offset + "s, is_dst: " + IsDst + ", zone name: " + Name;
                }
#else
        }
#endif
        }
}