/*
* Parsing begins with a call to GetFrontMatter function. It isolates the
* front matter from the markdown string given as argument. We also need
* the input file path for reporting possible errors. Nothing is read from
* the file, though.
*
* ParseFrontMatter returns the value of the special parameter `template`.
* This parameter controls which page template to use, and it needs to be
* reseted to its default value when it is not present. It works
* differently from other parameters which hold their value until a new
* value is set. If the `template` parameter is not present or the whole
* front matter is absent, null is returned.
*/
public string ParseFrontMatter(string frontMatter, string filePath)
{
string result = null;
if (frontMatter != null)
{
/*
* Now we can create a new YamlStream and load the front matter
* using it. The parameters can be iterated through as simple
* key-value pairs.
*/
try
{
var yamlStream = new YamlStream();
yamlStream.Load(new StringReader(frontMatter));
var mapping = (YamlMappingNode)yamlStream.Documents[0].RootNode;
foreach (var entry in mapping.Children)
{
var key = entry.Key.ToString();
var value = entry.Value.ToString();
/*
* If we encounter the special parameter `template`, we store
* its value in the result. Special treatment is required also
* for parameters starting with underscore `_`. Those can
* contain markdown formatting and thus they are automatically
* converted to HTML.
*/
if (key.ToLower() == "template")
{
result = value;
}
else
{
_params.Add(key,
key.StartsWith("_") ?
Markdown.ToHtml(value, _pipeline) :
value);
}
}
}
/*
* Parsing errors are caught, supplemented with information on
* which input file the error occurred, and re-thrown to the
* main program which eventually reports them to the user.
*/
catch (YamlDotNet.Core.SyntaxErrorException e)
{
throw new LiterateException(
"Invalid syntax in the front matter. Make sure that the YAML data " +
"is defined according to the specification.",
filePath, "https://johtela.github.io/LiterateCS/FrontMatter.html", e);
}
}
return(result);
}
