Nearly all tests work

src/Nexus.Sources.StructuredFile/CustomDateTimeOffset.cs

@@ -0,0 +1,94 @@
+using System.Globalization;
+
+internal record struct CustomDateTimeOffset
+{
+    public CustomDateTimeOffset(DateTime dateTime, TimeSpan offset)
+    {
+        if (dateTime.Kind != DateTimeKind.Unspecified)
+            throw new Exception("Only Kind = DateTimeKind.Unspecified is allowed.");
+
+        DateTime = dateTime;
+        Offset = offset;
+
+        UtcDateTime = DateTime == default && Offset > TimeSpan.Zero
+            ? new DateTime(0, DateTimeKind.Utc)
+            : new DateTimeOffset(DateTime, Offset).UtcDateTime;
+    }
+
+    public DateTime DateTime { get; }
+
+    public DateTime UtcDateTime { get; }
+
+    public TimeSpan Offset { get; }
+
+    public static bool TryParseExact(
+        string input, 
+        string format,
+        TimeSpan utcOffset,
+        out CustomDateTimeOffset dateTimeOffset)
+    {
+        dateTimeOffset = default;
+
+        var result1 = DateTime.TryParseExact(
+            input,
+            format,
+            default,
+            DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal | DateTimeStyles.NoCurrentDateDefault,
+            out var tmpDateTime
+        );
+
+        var result2 = DateTimeOffset.TryParseExact(
+            input,
+            format,
+            default,
+            DateTimeStyles.AssumeUniversal,
+            out var tmpDateTimeOffset
+        );
+
+        if (!result1 || !result2)
+            return false;
+
+        /* This happens when there is no date in the input string 
+         * (see also 'NoCurrentDateDefault', which does not work
+         * for DateTimeOffset) 
+         */
+        if (tmpDateTime.Date != tmpDateTimeOffset.UtcDateTime.Date)
+        {
+            dateTimeOffset = new CustomDateTimeOffset(
+                new DateTime(01, 01, 0001) + tmpDateTimeOffset.TimeOfDay,
+                tmpDateTimeOffset.Offset
+            );
+        }
+
+        else
+        {
+            dateTimeOffset = FromDateTimeOffset(tmpDateTimeOffset);
+        }
+
+        /* timezone information in file path */
+        if (
+#warning improve
+            input.Contains("Z") ||
+            input.Contains("+"))
+        {
+            // do nothing
+        }
+
+        /* no timezone information in file path */
+        else
+        {
+            dateTimeOffset = new CustomDateTimeOffset
+            (
+                dateTimeOffset.DateTime, 
+                utcOffset
+            );
+        }
+
+        return true;
+    }
+
+    private static CustomDateTimeOffset FromDateTimeOffset(DateTimeOffset value)
+    {
+        return new CustomDateTimeOffset(value.DateTime, value.Offset);
+    }
+}