'use strict';
const crypto = require('crypto');

/** 空值不参与，字典序，MD5 小写 */
function buildSign(params, secretKey) {
  const keys = Object.keys(params).filter((k) => k !== 'Sign').sort();
  const parts = [];
  for (const k of keys) {
    const v = params[k];
    if (v === null || v === undefined) continue;
    const s = String(v);
    if (s === '') continue;
    parts.push(`${k}=${s}`);
  }
  const raw = parts.join('&') + `&SecretKey=${secretKey}`;
  return crypto.createHash('md5').update(raw, 'utf8').digest('hex');
}

module.exports = { buildSign };