splitFrontMatter function

({String body, Map<String, String> frontMatter}) splitFrontMatter(String raw)

Splits leading --- YAML front matter from the markdown body.

Only the flat key: value pairs docs actually use are read; anything more structured (nested maps, lists) is skipped rather than mis-parsed.

Implementation

({Map<String, String> frontMatter, String body}) splitFrontMatter(String raw) {
  final normalized = raw.replaceAll('\r\n', '\n');
  if (!normalized.startsWith('---\n')) {
    return (frontMatter: const {}, body: normalized);
  }

  final end = normalized.indexOf('\n---', 3);
  if (end < 0) return (frontMatter: const {}, body: normalized);

  final block = normalized.substring(4, end);
  final body = normalized.substring(normalized.indexOf('\n', end + 1) + 1);

  final frontMatter = <String, String>{};
  String? key;
  final folded = StringBuffer();

  void flush() {
    final pending = key;
    if (pending != null && folded.isNotEmpty) {
      frontMatter[pending] = folded.toString().trim();
    }
    folded.clear();
  }

  for (final line in block.split('\n')) {
    final match = RegExp(r'^([A-Za-z_][\w-]*):\s*(.*)$').firstMatch(line);
    if (match != null) {
      flush();
      key = match.group(1);
      final value = match.group(2)!.trim();
      // `>-` / `|` introduce a folded block; its lines follow indented.
      folded.write(
        value == '>-' || value == '>' || value == '|' ? '' : _unquote(value),
      );
    } else if (key != null && line.startsWith(RegExp(r'\s'))) {
      folded.write(' ${line.trim()}');
    }
  }
  flush();

  return (frontMatter: frontMatter, body: body);
}