/// <summary>
/// Tries to match a block opening.
/// </summary>
/// <param name="processor">The parser processor.</param>
/// <returns>The result of the match</returns>
public override BlockState TryOpen(BlockProcessor processor)
{
// We expect no indentation for a fenced code block.
if (processor.IsCodeIndent)
{
return(BlockState.None);
}
// Only accept a frontmatter at the beginning of the file
if (processor.Start != 0)
{
return(BlockState.None);
}
int count = 0;
var line = processor.Line;
char c = line.CurrentChar;
// Must consist of exactly three dashes
while (c == '-' && count < 4)
{
count++;
c = line.NextChar();
}
// If three dashes (optionally followed by whitespace)
// this is a YAML front matter block
if (count == 3 && (c == '\0' || c.IsWhitespace()) && line.TrimEnd())
{
bool hasFullYamlFrontMatter = false;
// We make sure that there is a closing frontmatter somewhere in the document
// so here we work on the full document instead of just the line
var fullLine = new StringSlice(line.Text, line.Start, line.Text.Length - 1);
c = fullLine.CurrentChar;
while (c != '\0')
{
c = fullLine.NextChar();
if (c == '\n' || c == '\r')
{
var nc = fullLine.PeekChar();
if (c == '\r' && nc == '\n')
{
c = fullLine.NextChar();
}
nc = fullLine.PeekChar();
if (nc == '-')
{
if (fullLine.NextChar() == '-' && fullLine.NextChar() == '-' && fullLine.NextChar() == '-' && (fullLine.NextChar() == '\0' || fullLine.SkipSpacesToEndOfLineOrEndOfDocument()))
{
hasFullYamlFrontMatter = true;
break;
}
}
else if (nc == '.')
{
if (fullLine.NextChar() == '.' && fullLine.NextChar() == '.' && fullLine.NextChar() == '.' && (fullLine.NextChar() == '\0' || fullLine.SkipSpacesToEndOfLineOrEndOfDocument()))
{
hasFullYamlFrontMatter = true;
break;
}
}
}
}
if (hasFullYamlFrontMatter)
{
// Create a front matter block
var block = this.CreateFrontMatterBlock(processor);
block.Column = processor.Column;
block.Span.Start = 0;
block.Span.End = line.Start;
// Store the number of matched string into the context
processor.NewBlocks.Push(block);
// Discard the current line as it is already parsed
return(BlockState.ContinueDiscard);
}
}
return(BlockState.None);
}