/**
 * Detect and collapse degenerate generation loops. No Bare imports.
 *
 * Small Qwen runs with no predict cap will repeat a clause until the idle
 * timeout. Catch the repeating tail and stop the stream.
 */

function repeatingUnit(text, minLen, copies) {
  const s = String(text || '');
  const min = minLen > 0 ? minLen : 24;
  const need = copies > 0 ? copies : 3;
  if (s.length < min * need) return '';
  const window = s.length > 2400 ? s.slice(-2400) : s;
  const maxLen = Math.min(180, Math.floor(window.length / need));
  for (let len = min; len <= maxLen; len++) {
    const unit = window.slice(-len);
    if (unit.replace(/\s+/g, '').length < 12) continue;
    let matched = true;
    for (let i = 2; i <= need; i++) {
      if (window.slice(-len * i, -len * (i - 1)) !== unit) {
        matched = false;
        break;
      }
    }
    if (matched) return unit;
  }
  return '';
}

function isRepeating(text) {
  return !!repeatingUnit(text);
}

function escapeRe(value) {
  return String(value).replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}

function collapseRepeats(text) {
  const s = String(text || '');
  const unit = repeatingUnit(s);
  if (!unit) return s.trim();
  return s.replace(new RegExp('(?:' + escapeRe(unit) + '){3,}$'), unit).trim();
}

module.exports = { repeatingUnit, isRepeating, collapseRepeats };