// "Luke 1, Luke 2, Luke 3, Luke 5" -> "Luke 1–3, 5": a long run of chapters reads as ranges, so a
// study card stays short. Anything that isn't "Book N" is left as it was.
export function compactPassages(summary) {
  if (!summary) return '';
  const parts = summary.split(/,\s*/);
  const groups = [];
  for (const part of parts) {
    const m = part.match(/^(.+?)\s+(\d+)$/);
    if (!m) { groups.push({ raw: part }); continue; }
    const last = groups[groups.length - 1];
    if (last && last.book === m[1]) last.chapters.push(Number(m[2]));
    else groups.push({ book: m[1], chapters: [Number(m[2])] });
  }
  return groups.map((g) => {
    if (g.raw !== undefined) return g.raw;
    const runs = [];
    for (const n of g.chapters) {
      const run = runs[runs.length - 1];
      if (run && n === run[1] + 1) run[1] = n; else runs.push([n, n]);
    }
    return `${g.book} ${runs.map(([a, b]) => (a === b ? a : b === a + 1 ? `${a}, ${b}` : `${a}–${b}`)).join(', ')}`;
  }).join(', ');
}