gistfile1.txt

using Microsoft.Graph.Models;
using System.Globalization;

namespace MsGraph.Reproduction;

public class MsGraphReproduction
{
    [Fact]
    public void ZonedDateTime_Maps_Time_UTC()
    {
        // Arrange
        DateTime start = new DateTime(2023, 6, 1, 10, 0, 0, DateTimeKind.Utc);
        var zoned = new DateTimeTimeZone
        {
            DateTime = start.ToString("o"),
            TimeZone = "UTC"
        };
        //Fails as ToDateTimeOffset does not use DateTimeStyles.RoundtripKind
        var offset = zoned.ToDateTimeOffset();
        Assert.Equal(offset.UtcDateTime, start);
    }

    // The main path we took, changing the DateTimeStyles to RoundtripKind works.
    DateTimeOffset ToOffset(DateTimeTimeZone dateTimeTimeZone)
    {
        DateTime dateTime = DateTime.ParseExact(dateTimeTimeZone.DateTime, "yyyy-MM-ddTHH:mm:ss.fffffffK", CultureInfo.InvariantCulture, DateTimeStyles.RoundtripKind);
        TimeZoneInfo timeZoneInfo = TimeZoneInfo.FindSystemTimeZoneById(dateTimeTimeZone.TimeZone);
        dateTime = DateTime.SpecifyKind(dateTime, DateTimeKind.Utc);
        var offset = timeZoneInfo.GetUtcOffset(dateTime);
        return new DateTimeOffset(dateTime, offset);
    }
}