import dgram from 'dgram';
import dnsPacket from 'dns-packet';
import { records } from './dns-records.js';

const server = dgram.createSocket('udp4');
const PORT = 53;

server.on('error', (err) => {
  console.error(`服务器异常：\n${err.stack}`);
  server.close();
});

server.on('message', (msg, rinfo) => {
  console.log(`收到来自 ${rinfo.address}:${rinfo.port} 的DNS查询`);

  const request = dnsPacket.decode(msg);
  // 确保至少有一个问题
  if (!request.questions || request.questions.length === 0) {
    return;
  }
  const question = request.questions[0];

  console.log(`查询的域名: ${question.name}, 类型: ${question.type}`);

  // 只处理 A 记录查询 (IPv4)
  if (question.type !== 'A') {
    // 对于非A记录查询，可以不响应或发送适当的错误
    return;
  }

  const domain = question.name;
  const ip = records[domain];

  let response;

  if (ip) {
    console.log(`为 ${domain} 找到IP: ${ip}`);
    response = dnsPacket.encode({
      type: 'response',
      id: request.id,
      flags: dnsPacket.AUTHORITATIVE_ANSWER,
      questions: request.questions,
      answers: [{
        type: 'A',
        class: 'IN',
        name: domain,
        ttl: 300, // Time-to-live
        data: ip,
      }],
    });
  } else {
    console.log(`未找到域名 ${domain} 的记录`);
    response = dnsPacket.encode({
      type: 'response',
      id: request.id,
      flags: dnsPacket.AUTHORITATIVE_ANSWER | dnsPacket.RECURSION_AVAILABLE,
      questions: request.questions,
      rcode: 'NXDOMAIN' // Non-Existent Domain
    });
  }

  server.send(response, rinfo.port, rinfo.address, (err) => {
    if (err) {
      console.error('发送响应失败:', err);
    } else {
      console.log(`已向 ${rinfo.address}:${rinfo.port} 发送响应`);
    }
  });
});

server.on('listening', () => {
  const address = server.address();
  console.log(`DNS 服务器正在监听 ${address.address}:${address.port}`);
});

server.bind(PORT, () => {
  // 在 Windows 上，可能需要管理员权限才能绑定到 53 端口
  if (process.platform === 'win32') {
    console.log('在 Windows 上运行，请确保您有管理员权限来绑定到53端口。');
  }
});