T4 Template for conversion of IANA and Windows time zones.

TimeZoneInfoConverter.tt

<#@ template debug="false" hostspecific="true" language="C#" #>
<#@ output extension=".g.cs" #>
<#@ assembly name="EnvDTE" #>
<#@ assembly name="System.Text.Json" #>
<#@ assembly name="System.Memory" #>
<#@ assembly name="netstandard" #>
<#@ import namespace="System.IO" #>
<#@ import namespace="System.Net" #>
<#@ import namespace="System.Text.Json" #>
<#
var unicodeDownloadUrl =
  "https://raw.githubusercontent.com/unicode-cldr/cldr-core/master/supplemental/"
  + "windowsZones.json";

string json;
using (var client = new WebClient())
{
    json = client.DownloadString(unicodeDownloadUrl);
}

var jsonDoc = JsonDocument.Parse(json);

var rootElement = jsonDoc.RootElement;
var supplemental = rootElement.GetProperty("supplemental");
var windowsZones = supplemental.GetProperty("windowsZones");
var mapTimezones = windowsZones.GetProperty("mapTimezones");

#>
using System;
using System.Collections.Generic;
using System.Linq;
using cyontec.Annotations;

namespace lennybacon.Globalization {
  /// <summary>
  ///   Converts timezones between IANA and windows format.
  /// </summary>
  public class TimeZoneInfoConverter{
#region _ianaToWindowsTimeZones
    [NotNull]
    private static readonly List<KeyValuePair<string, string>> _s_ianaToWinTz =
      new List<KeyValuePair<string, string>> {
<#
foreach(var item in mapTimezones.EnumerateArray()){
  var mapZone = item.GetProperty("mapZone");
  var ianaTimeZones = mapZone.GetProperty("_type").GetString().Split(' ');
  var windowsTimeZone = mapZone.GetProperty("_other").GetString();
  foreach(var ianaTimeZone in ianaTimeZones){
#>
          new KeyValuePair<string, string>(
            "<#=ianaTimeZone.Replace("_", " ")#>",
            "<#=windowsTimeZone#>"
          ),
<#
  }
}
#>
    };
#endregion


    /// <summary>
    ///   Gets the IANA time zones.
    /// </summary>
    /// <returns>IEnumerable{System.String}.</returns>
    [UsedImplicitly]
    [NotNull]
    public static IEnumerable<string> GetIanaTimeZones() {
      return _s_ianaToWinTz.Select(kvp => kvp.Key);
    }

    /// <summary>
    ///   Gets the IANA time zones by windows time zone.
    /// </summary>
    /// <param name="windowsTimeZone">The windows time zone.</param>
    /// <returns>IEnumerable{System.String}.</returns>
    [UsedImplicitly]
    [NotNull]
    public static IEnumerable<string> GetIanaTimeZones(TimeZoneInfo windowsTimeZone) {
      if (windowsTimeZone?.Id == null) {
        throw new ArgumentNullException(nameof(windowsTimeZone));
      }

      return GetIanaTimeZones(windowsTimeZone.Id);
    }

    /// <summary>
    ///   Gets the IANA time zone by windows time zone id.
    /// </summary>
    /// <param name="windowsTimeZoneId">
    ///   The windows time zone unique
    ///   identifier.
    /// </param>
    /// <returns>IEnumerable{System.String}.</returns>
    [UsedImplicitly]
    [NotNull]
    public static IEnumerable<string> GetIanaTimeZones(string windowsTimeZoneId) {
      if (windowsTimeZoneId == null) {
        throw new ArgumentNullException(nameof(windowsTimeZoneId));
      }

      return _s_ianaToWinTz
        .Where(
          tz => string.Equals(tz.Value, windowsTimeZoneId, StringComparison.Ordinal))
        .Select(tz => tz.Key);
    }

    /// <summary>
    ///   Gets the window time zone unique identifiers.
    /// </summary>
    /// <returns>IEnumerable{System.String}.</returns>
    [UsedImplicitly]
    [NotNull]
    public static IEnumerable<string> GetWindowTimeZoneIds() {
      return TimeZoneInfo.GetSystemTimeZones()
                         .Where(tz => tz != null)
                         .Select(tz => tz.Id);
    }

    /// <summary>
    ///   Gets the window time zone unique identifiers by IANA time zone info.
    /// </summary>
    /// <param name="ianaTimeZone">The IANA time zone.</param>
    /// <returns>IEnumerable{System.String}.</returns>
    [UsedImplicitly]
    [NotNull]
    public static IEnumerable<string> GetWindowTimeZoneIds(string ianaTimeZone) {
      return _s_ianaToWinTz
             .Where(tz => string.Equals(tz.Key, ianaTimeZone, StringComparison.Ordinal))
             .Select(tz => tz.Value);
    }

    /// <summary>
    ///   Gets the window time zone information by IANA time zone info.
    /// </summary>
    /// <param name="ianaTimeZone">The IANA time zone.</param>
    /// <returns>IEnumerable{TimeZoneInfo}.</returns>
    [UsedImplicitly]
    [NotNull]
    public static IEnumerable<TimeZoneInfo> GetWindowTimeZoneInfos(string ianaTimeZone) {
      return GetWindowTimeZoneIds(ianaTimeZone)
        .Select(TimeZoneInfo.FindSystemTimeZoneById);
    }


    /// <summary>
    ///   Gets the window time zone information.
    /// </summary>
    /// <returns>IEnumerable{TimeZoneInfo}.</returns>
    [UsedImplicitly]
    [NotNull]
    public static IEnumerable<TimeZoneInfo> GetWindowTimeZoneInfos() {
      return TimeZoneInfo.GetSystemTimeZones();
    }
  }
}