mono datetime offset workaround

PlexRequests.Helpers/DateTimeHelper.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 
 namespace PlexRequests.Helpers
 {
@@ -6,9 +7,20 @@ namespace PlexRequests.Helpers
     {
         public static DateTimeOffset OffsetUTCDateTime(DateTime utcDateTime, int minuteOffset)
         {
-            TimeSpan ts = TimeSpan.FromMinutes(-minuteOffset);
-            return new DateTimeOffset(utcDateTime).ToOffset(ts);
+            //TimeSpan ts = TimeSpan.FromMinutes(-minuteOffset);
+            //return new DateTimeOffset(utcDateTime).ToOffset(ts);
+
+            // this is a workaround below to work with MONO
+            var tzi = FindTimeZoneFromOffset(minuteOffset);
+            var utcOffset = tzi.GetUtcOffset(utcDateTime);
+            var newDate = utcDateTime + utcOffset;
+            return new DateTimeOffset(newDate.Ticks, utcOffset);
         }
 
+        private static TimeZoneInfo FindTimeZoneFromOffset(int minuteOffset)
+        {
+            var tzc = TimeZoneInfo.GetSystemTimeZones();
+            return tzc.FirstOrDefault(x => x.BaseUtcOffset.TotalMinutes == -minuteOffset);
+        }
     }
 }