TimeZone.cs

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using System;
using System.IO;
 
using IKVM.Runtime;
 
namespace IKVM.Java.Externs.java.util
{
 
    static class TimeZone
    {
 
        static string GetCurrentTimeZoneID()
        {
            return TimeZoneInfo.Local.Id;
        }
 
        static string MatchJavaTZ(string javaHome, string tzName)
        {
            try
            {
                var mapFileName = Path.Combine(javaHome, "lib", "tzmappings");
                if (File.Exists(mapFileName) == false)
                    return null;
 
                using var mapFile = File.OpenText(mapFileName);
                string mapLine = null;
                while ((mapLine = mapFile.ReadLine()) != null)
                {
                    mapLine = mapLine.Trim();
                    if (mapLine.Length < 4)
                        continue;
                    if (mapLine[0] == '#')
                        continue;
 
                    var l = mapLine.Split(':');
                    if (l.Length < 4)
                        continue;
 
                    if (l[0] == tzName)
                        return l[3];
                }
 
                return null;
            }
            catch (IOException)
            {
                return null;
            }
        }
 
        public static string getSystemTimeZoneID(string javaHome)
        {
            if (RuntimeUtil.IsWindows)
                return MatchJavaTZ(javaHome, GetCurrentTimeZoneID()) ?? getSystemGMTOffsetID();
            else
                return GetCurrentTimeZoneID() ?? getSystemGMTOffsetID();
        }
 
        public static string getSystemGMTOffsetID()
        {
            var sp = TimeZoneInfo.Local.GetUtcOffset(DateTime.Now);
            var h = sp.Hours;
            var m = sp.Minutes;
            if (h == 0 && m == 0)
                return "GMT";
            else if (h >= 0 && m >= 0)
                return $"GMT+{h:D2}:{m:D2}";
            else
                return $"GMT-{-h:D2}:{-m:D2}";
        }
 
    }
 
}