const escapeRegex = (value: string): string => value.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');

const parseOptionalPositiveInt = (value: unknown, fieldName: string) => {
  const raw = String(value ?? '').trim();
  if (!raw) return { value: undefined as number | undefined };

  if (!/^\d+$/.test(raw)) {
    return { error: `${fieldName}必须是正整数` };
  }

  const parsed = Number(raw);
  if (!Number.isFinite(parsed) || parsed <= 0) {
    return { error: `${fieldName}必须大于0` };
  }

  return { value: parsed };
};

export const buildVocabularySummaryFilters = (query: Record<string, any>) => {
  const studentNo = String(query.studentNo || '').trim();
  const rawMinCorrectWords = query.minCorrectWords ?? query.minWords;
  const wordCountResult = parseOptionalPositiveInt(rawMinCorrectWords, '正确单词数量');
  if ('error' in wordCountResult) return { error: wordCountResult.error };

  const minCorrectWords = wordCountResult.value;
  const userMatchStages = studentNo
    ? [{
      $match: {
        'user.username': {
          $regex: escapeRegex(studentNo),
          $options: 'i'
        }
      }
    }]
    : [];

  const baseMatch: Record<string, any> = {};
  if (typeof minCorrectWords === 'number') {
    baseMatch['stats.correctWords'] = { $gte: minCorrectWords };
  }

  return {
    minCorrectWords,
    userMatchStages,
    baseMatch
  };
};