// kb-headers.mjs — Parse optional authority headers from KB reference files.
// Zero dependencies. Scans only the top of the file (header region) where the
// **Source:** / **Primary source:** line lives, mirroring report-changes'
// parseLastUpdated convention.

const HEADER_REGION_BYTES = 500;

const SOURCE_PATTERNS = [
  /\*\*Source:\*\*\s*(\S+)/i,
  /\*\*Primary source:\*\*\s*(\S+)/i,
];

/**
 * Extract the declared authority source URL from a KB reference file's header.
 * @param {string} content — full file content (only the first 500 bytes are scanned)
 * @returns {string|null} the source URL, or null if no header is present
 */
export function parseSourceHeader(content) {
  if (!content || typeof content !== 'string') return null;
  const head = content.slice(0, HEADER_REGION_BYTES);
  for (const pattern of SOURCE_PATTERNS) {
    const match = head.match(pattern);
    if (match) return match[1].trim();
  }
  return null;
}