private TFrontMatter?ParseFrontMatter <TFrontMatter>(StreamReader r)
where TFrontMatter : class, IMarkdownFrontMatter, new()
{
var deserializer = new DeserializerBuilder()
.WithNamingConvention(PascalCaseNamingConvention.Instance)
.BuildValueDeserializer();
var parser = new Parser(r);
parser.Consume <StreamStart>();
parser.Consume <DocumentStart>();
var result = (TFrontMatter?)deserializer.DeserializeValue(
parser,
typeof(TFrontMatter),
new SerializerState(),
deserializer);
// Currently, the parser has read all the document and stays at the last token of it (*before* closing `---`
// line). At the same time, it has already peeked the first character of the next line *after* the end of
// the document from the StreamReader instance.
//
// So, we have to rewind the stream. To do that, calculate position of the next document start token, and
// rewind the basic stream and the stream reader itself.
_ = parser.Consume <DocumentEnd>();
var nextDocumentStart = (DocumentStart)parser.Current !;
var position = nextDocumentStart.End.Index // points *before* the closing `---`
+ 1; // points to the first character of closing `---`
RewindReaderTo(r, position);
_ = r.ReadLine(); // should be `---`
return(result);
