/**
 * Returns the group names from an Xref header,
 * e.g. `news.eweka.nl alt.binaries.test:123 alt.binaries.x:456`.
 */
export function parseXrefGroups(xref: string | undefined): string[] {
  if (!xref) return []
  return xref
    .trim()
    .split(/\s+/)
    .slice(1)
    .map((entry) => entry.slice(0, entry.lastIndexOf(':')))
    .filter(Boolean)
}