System.TimeZoneInfo.IsDaylightSavingTime C# (CSharp) Method

		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;
		}

        private static void Dump(TimeZoneInfo zone, Options options, TextWriter writer)
        {
            writer.Write($"{zone.Id}\n");

            // This will be a bit odd using Windows time zones, as most have permanent
            // daylight saving rules... but for tz data, it should be okay.
            var initial = new DateTimeOffset(2, 1, 1, 0, 0, 0, 0, TimeSpan.Zero);
            var initialOffset = zone.GetUtcOffset(initial);
            var initialDaylight = zone.IsDaylightSavingTime(initial);
            writer.Write("Initially:           {0} {1} {2}\n",
                (initialOffset.Ticks >= 0 ? "+" : "-") + initialOffset.ToString("hh':'mm':'ss", CultureInfo.InvariantCulture),
                initialDaylight ? "daylight" : "standard",
                initialDaylight ? zone.DaylightName : zone.StandardName);

            int fromYear = options.FromYear ?? 1800;
            DateTimeOffset start = new DateTimeOffset(fromYear, 1, 1, 0, 0, 0, TimeSpan.Zero);
            DateTimeOffset end = new DateTimeOffset(options.ToYear, 1, 1, 0, 0, 0, TimeSpan.Zero);

            DateTimeOffset? transition = GetNextTransition(zone, start.AddTicks(-1), end);
            while (transition != null)
            {
                var offset = zone.GetUtcOffset(transition.Value);
                var isDaylight = zone.IsDaylightSavingTime(transition.Value);
                // It's unfortunate that TimeZoneInfo doesn't support the idea of different names
                // for different periods in history. Never mind - this is better than nothing,
                // for diagnostic purposes.
                writer.Write("{0} {1} {2} {3}\n",
                    transition.Value.ToString("yyyy-MM-dd HH:mm:ss'Z'", CultureInfo.InvariantCulture),
                    (offset.Ticks >= 0 ? "+" : "-") + offset.ToString("hh':'mm':'ss", CultureInfo.InvariantCulture),
                    isDaylight ? "daylight" : "standard",
                    isDaylight ? zone.DaylightName : zone.StandardName);
                transition = GetNextTransition(zone, transition.Value, end);
            }
            writer.Write("\n");
        }