/**
 * 数据库分页查询工具函数
 * @module services/utils/pagination
 */

/**
 * 分页查询函数
 * @param {Function} queryFn - 数据库查询函数
 * @param {string} sql - SQL 查询语句
 * @param {Array} params - SQL 参数
 * @param {number} [page=1] - 页码
 * @param {number} [pageSize=20] - 每页大小
 * @returns {Promise<Object>} 分页结果 { data, total, page, pageSize, totalPages }
 */
async function paginate(queryFn, sql, params, page = 1, pageSize = 20) {
  const p = Math.max(1, parseInt(page) || 1)
  const ps = Math.min(100, Math.max(1, parseInt(pageSize) || 20))

  const countResult = await queryFn(
    `SELECT COUNT(*) as total FROM (${sql}) AS _paged`,
    params
  )
  const total = countResult[0].total
  const totalPages = Math.ceil(total / ps)

  const offset = (p - 1) * ps
  const data = await queryFn(
    `${sql} LIMIT ${ps} OFFSET ${offset}`,
    params
  )

  return { data, total, page: p, pageSize: ps, totalPages }
}

module.exports = { paginate }