// okf-frontmatter.mjs
// Minimal TOP-LEVEL frontmatter reader for the shared OKF conformance checker.
// Provenance: vendored from okr's lib/frontmatter.mjs at c06e4d7 so the catalog-hosted
// checker is self-contained — zero npm dependencies, no cross-repo import. The checker
// only reads (never writes), so only parseFrontmatter().get is vendored. okr has since
// added BOM/CRLF normalization here (lib/frontmatter.mjs:23); this copy has not, so the
// two have diverged and are no longer byte-identical (parity is the parity-gate's job,
// not this file's).
//
// SECOND, DELIBERATE DIVERGENCE (2026-08-01): the key is anchored at column 0 here, while
// okr keeps `^\s*key:`. That is not okr lagging — their reader is SHARED, and the nested
// match is load-bearing for their injector (lib/frontmatter.mjs:7-9 -> inject:69). A
// conformance checker needs the opposite: §4.1's keys are top-level, and `sources[]`
// entries carry their own `resource`/`title`/`type`. Pinned as parity fixture
// `red-nested-key`.

const FM_RE = /^---\n([\s\S]*?)\n---/;

export function parseFrontmatter(content) {
  const match = String(content).match(FM_RE);
  const raw = match ? match[1] : null;

  const get = (key) => {
    if (raw === null) return null;
    // Anchored at column 0: OKF's §4.1 keys are TOP-LEVEL keys. `sources[]` entries carry their
    // own `resource`/`title`/`type` (§5:302), and §? :467-469 names them as distinct fields from
    // the same-named top-level ones. A leading \s* matched those nested entries and reported the
    // top-level key as present — a false negative, on `type` too (§4.1's only required field).
    const m = raw.match(new RegExp(`^${key}:\\s*(.*)$`, 'm'));
    if (!m) return null;
    let v = m[1].trim();
    if (v === '') return null;
    const q = v[0];
    if (q === '"' || q === "'") {
      const end = v.indexOf(q, 1);
      if (end !== -1) return v.slice(1, end); // internal '#' preserved
      v = v.slice(1); // unterminated quote: fall back to the rest
    } else {
      v = v.replace(/\s+#.*$/, '').trim(); // unquoted: strip trailing comment
    }
    return v === '' ? null : v;
  };

  return { raw, get };
}