function parseJsonSafe(value) {
  if (!value) {
    return null;
  }
  if (typeof value === 'object') {
    return value;
  }
  try {
    return JSON.parse(value);
  } catch (_error) {
    return null;
  }
}

function readFormArray(body, key) {
  if (Array.isArray(body[key])) {
    return body[key];
  }
  if (body[key] === undefined) {
    return [];
  }
  return [body[key]];
}

function normalizePageNumber(value) {
  const pageNumber = Math.floor(Number(value) || 1);
  return Math.max(1, pageNumber);
}

async function fetchPagedRows(pool, options) {
  const selectSql = String(options && options.selectSql || '').trim();
  const countSql = String(options && options.countSql || '').trim();
  const params = Array.isArray(options && options.params) ? options.params : [];
  const pageSize = Math.max(1, Number(options && options.pageSize) || 10);
  const currentPage = normalizePageNumber(options && options.page);

  if (!selectSql || !countSql) {
    throw new Error('fetchPagedRows requires selectSql and countSql.');
  }

  const [countRows] = await pool.query(countSql, params);
  const totalItems = Number(countRows && countRows[0] && countRows[0].count) || 0;
  const totalPages = Math.max(1, Math.ceil(totalItems / pageSize));
  const safeCurrentPage = Math.min(currentPage, totalPages);
  const offset = (safeCurrentPage - 1) * pageSize;
  const [rows] = await pool.query(`${selectSql} LIMIT ? OFFSET ?`, params.concat([pageSize, offset]));

  return {
    rows: rows || [],
    totalItems: totalItems,
    totalPages: totalPages,
    currentPage: safeCurrentPage,
    pageSize: pageSize
  };
}

async function fetchDuplicateName(pool, tableName, name, excludeId, columnName) {
  const normalizedName = String(name || '').trim();
  if (!normalizedName) {
    return null;
  }

  const normalizedColumnName = String(columnName || 'name').trim() || 'name';
  const params = [normalizedName];
  let sql = `SELECT id, \`${normalizedColumnName}\` AS name FROM \`${tableName}\` WHERE LOWER(TRIM(\`${normalizedColumnName}\`)) = LOWER(TRIM(?))`;
  if (excludeId !== undefined && excludeId !== null) {
    sql += ' AND id <> ?';
    params.push(excludeId);
  }
  sql += ' LIMIT 1';

  const [rows] = await pool.query(sql, params);
  return rows[0] || null;
}

module.exports = {
  parseJsonSafe,
  readFormArray,
  normalizePageNumber,
  fetchPagedRows,
  fetchDuplicateName
};