function mergeChecklistConflict({ baseBody, localBody, remoteBody }) {
  const taskPattern = /^(\s*[-*+]\s+\[)([ xX])(\]\s+)(.*)$/;

  function tasks(body) {
    const entries = [];
    String(body || '').split('\n').forEach((line, lineIndex) => {
      const match = line.match(taskPattern);
      if (!match) return;
      const label = match[4].trim();
      const key = label.replace(/\s+/g, ' ').toLocaleLowerCase();
      if (!key) return;
      entries.push({ key, label, checked: match[2].toLowerCase() === 'x', lineIndex, match });
    });
    return entries;
  }

  function grouped(entries) {
    const result = new Map();
    entries.forEach(entry => result.set(entry.key, [...(result.get(entry.key) || []), entry]));
    return result;
  }

  const base = grouped(tasks(baseBody));
  const local = grouped(tasks(localBody));
  const remoteEntries = tasks(remoteBody);
  const remote = grouped(remoteEntries);
  const changes = [];
  const conflicts = [];

  for (const [key, baseMatches] of base) {
    const localMatches = local.get(key) || [];
    if (baseMatches.length !== 1 || localMatches.length !== 1) continue;
    if (baseMatches[0].checked === localMatches[0].checked) continue;
    const remoteMatches = remote.get(key) || [];
    if (remoteMatches.length !== 1) {
      conflicts.push({
        label: baseMatches[0].label,
        reason: remoteMatches.length ? 'ambiguous' : 'missing',
      });
      continue;
    }
    changes.push({ label: remoteMatches[0].label, checked: localMatches[0].checked });
  }

  if (conflicts.length) return { body: null, changes, conflicts };
  const desired = new Map(changes.map(change => [
    change.label.replace(/\s+/g, ' ').toLocaleLowerCase(), change.checked,
  ]));
  const lines = String(remoteBody || '').split('\n');
  remoteEntries.forEach(entry => {
    if (!desired.has(entry.key)) return;
    const marker = desired.get(entry.key) ? 'x' : ' ';
    lines[entry.lineIndex] = entry.match[1] + marker + entry.match[3] + entry.match[4];
  });
  return { body: lines.join('\n'), changes, conflicts: [] };
}

if (typeof module !== 'undefined') module.exports = mergeChecklistConflict;