Validate inferred time zone offsets

.gitignore

@@ -198,3 +198,6 @@ FakesAssemblies/
 
 # Jetbrains Rider
 .idea/
+
+# VSCode
+.vscode/

ISOv4Plugin/Mappers/LoggedDataMappers/Import/SpatialRecordMapper.cs

@@ -49,7 +49,11 @@ public IEnumerable<SpatialRecord> Map(IEnumerable<ISOSpatialRow> isoSpatialRows,
                         pan.AllocationStamp.Start.Value.Minute == firstSpatialRow.TimeStart.Minute &&
                         pan.AllocationStamp.Start.Value.Second == firstSpatialRow.TimeStart.Second)
                     {
-                        _effectiveTimeZoneOffset = firstSpatialRow.TimeStart - pan.AllocationStamp.Start.Value;
+                        _effectiveTimeZoneOffset = TaskDataMapper.ValidateTimezoneOffset(firstSpatialRow.TimeStart, pan.AllocationStamp.Start.Value);
+                        if (!_effectiveTimeZoneOffset.HasValue)
+                        {
+                            _taskDataMapper.AddError($"Unable to determine effective timezone offset from comparison of spatial record and product allocation timestamps.  Monitor date/time setting may be invalid.");
+                        }
                     }
                 }
             }
@@ -202,22 +206,24 @@ private bool GovernsTimestamp(ISOProductAllocation p, SpatialRecord spatialRecor
 
         // Comparing DateTime values with different Kind values leads to inaccurate results.
         // Convert DateTimes to UTC if possible before comparing them
-        private DateTime? ToUtc(DateTime? nullableDateTime, TimeSpan? timezoneOffset)
+        private static DateTime? ToUtc(DateTime? nullableDateTime, TimeSpan? timezoneOffset)
         {
             return nullableDateTime.HasValue ? ToUtc(nullableDateTime.Value, timezoneOffset) : nullableDateTime;
         }
 
-        private DateTime ToUtc(DateTime dateTime, TimeSpan? timezoneOffset)
+        private static DateTime ToUtc(DateTime dateTime, TimeSpan? timezoneOffset)
         {
             if (dateTime.Kind == DateTimeKind.Utc)
                 return dateTime;
 
-            if (_taskDataMapper.TimezoneOffset.HasValue)
+            if (timezoneOffset.HasValue)
             {
                 // Convert from local time to UTC using the timezone offset.
+                // We're relying on the upstream guard ensuring the timezone offset is
+                // within 14 hours
                 var localTime = new DateTimeOffset(dateTime.Year, dateTime.Month, dateTime.Day, 
                     dateTime.Hour, dateTime.Minute, dateTime.Second, dateTime.Millisecond,
-                    _taskDataMapper.TimezoneOffset.Value);
+                    timezoneOffset.Value);
                 DateTime utc = localTime.UtcDateTime;
                 return utc;
             }

ISOv4Plugin/Mappers/TaskDataMapper.cs

@@ -157,6 +157,27 @@ public void AddError(string error, string id = null, string source = null, strin
             Errors.Add(new Error() { Description = error, Id = id, Source = source, StackTrace = stackTrace });
         }
 
+        /// <summary>
+        /// Validates and processes a timezone offset calculated from local and UTC times.
+        /// Calculates offset = localTime - utcTime, rounds to nearest minute, and validates it's within ±14 hours.
+        /// </summary>
+        /// <returns>The validated TimeSpan offset, or null if the offset is outside the acceptable ±14 hour range.</returns>
+        public static TimeSpan? ValidateTimezoneOffset(DateTime localTime, DateTime utcTime)
+        {
+            TimeSpan offset = localTime - utcTime;
+            // Round offset to nearest minute for use in timezone offset
+            offset = TimeSpan.FromMinutes(Math.Round(offset.TotalMinutes));
+            // DateTimeOffset requires the offset to be within ±14 hours
+            if (Math.Abs(offset.TotalHours) <= 14)
+            {
+                return offset;
+            }
+            else
+            {
+                return null;
+            }
+        }
+
         public ISO11783_TaskData Export(ApplicationDataModel.ADM.ApplicationDataModel adm)
         {
             AdaptDataModel = adm;

ISOv4Plugin/Mappers/TimeLogMapper.cs

@@ -330,11 +330,17 @@ protected IEnumerable<OperationData> ImportTimeLog(ISOTask loggedTask, ISOTimeLo
                         var firstRecord = isoRecords.FirstOrDefault(r => r.GpsUtcDateTime.HasValue && r.GpsUtcDate != ushort.MaxValue && r.GpsUtcDate != 0);
                         if (firstRecord != null)
                         {
-                            //Local - UTC = Delta.  This value will be rough based on the accuracy of the clock settings
+                            // Local - UTC = Delta.  This value will be rough based on the accuracy of the clock settings
                             // but will expose the ability to derive the UTC times from the exported local times.
-                            TimeSpan offset = firstRecord.TimeStart - firstRecord.GpsUtcDateTime.Value;
-                            // Round offset to nearest minute for use in timezone offset
-                            TaskDataMapper.TimezoneOffset = TimeSpan.FromMinutes(Math.Round(offset.TotalMinutes));
+                            TimeSpan? offset = TaskDataMapper.ValidateTimezoneOffset(firstRecord.TimeStart, firstRecord.GpsUtcDateTime.Value);
+                            if (offset.HasValue)
+                            {
+                                TaskDataMapper.TimezoneOffset = offset.Value;
+                            }
+                            else
+                            {
+                                TaskDataMapper.AddError($"GPS time offset of {firstRecord.TimeStart - firstRecord.GpsUtcDateTime.Value} is outside the acceptable range.  Monitor date/time setting is probably invalid. Product allocation logic may be impacted.");
+                            }
                         }
                     }
                 }