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

// Cloud gateway query parameters + the exact, unread JSON body. Algorithm:
// https://developer.alibaba.com/docs/doc.htm?articleId=121746&docType=1&treeId=832
function signature(params, body, secret) {
  const method = params.sign_method || '';
  if (!['', 'md5', 'hmac', 'hmac_md5', 'hmac_sha256'].includes(method)) return null;
  const content = Object.keys(params).filter(key => key !== 'sign' && params[key] !== '').sort()
    .map(key => key + params[key]).join('') + body;
  if (method === 'hmac' || method === 'hmac_md5' || method === 'hmac_sha256') {
    return crypto.createHmac(method === 'hmac_sha256' ? 'sha256' : 'md5', secret).update(content).digest('hex').toUpperCase();
  }
  return crypto.createHash('md5').update((method === 'md5' ? secret : '') + content + secret).digest('hex').toUpperCase();
}
function verify(url, body, env = process.env) {
  if (!env.TAOBAO_APP_KEY || !env.TAOBAO_APP_SECRET) return null;
  const params = Object.create(null);
  for (const [key, value] of new URL(url, 'http://localhost').searchParams) {
    if (key in params) return null; // Never ambiguously verify duplicate parameters.
    params[key] = value;
  }
  if (params.app_key !== env.TAOBAO_APP_KEY || !/^[A-Za-z0-9_-]{4,256}$/.test(params.open_id || '') ||
      !/^[A-Fa-f0-9]{32,64}$/.test(params.sign || '')) return null;
  const expected = signature(params, body, env.TAOBAO_APP_SECRET);
  if (!expected || expected.length !== params.sign.length ||
      !crypto.timingSafeEqual(Buffer.from(expected), Buffer.from(params.sign.toUpperCase()))) return null;
  // Login challenge is single-use and signed inside the body, preventing replay.
  return { providerKey: crypto.createHash('sha256').update(params.app_key + ':' + params.open_id).digest('hex') };
}
module.exports = { signature, verify };