import { createConnection } from 'net';
import type { VercelRequest, VercelResponse } from '@vercel/node';

// TLD to WHOIS server mapping
const WHOIS_SERVERS: Record<string, string> = {
  // Generic TLDs
  com: 'whois.verisign-grs.com',
  net: 'whois.verisign-grs.com',
  org: 'whois.pir.org',
  info: 'whois.afilias.net',
  biz: 'whois.biz',

  // Popular new gTLDs
  io: 'whois.nic.io',
  co: 'whois.registry.co',
  me: 'whois.nic.me',
  tv: 'whois.nic.tv',
  cc: 'whois.nic.cc',
  app: 'whois.nic.google',
  dev: 'whois.nic.google',
  xyz: 'whois.nic.xyz',
  online: 'whois.nic.online',
  site: 'whois.nic.site',
  tech: 'whois.nic.tech',
  shop: 'whois.nic.shop',
  blog: 'whois.nic.blog',
  club: 'whois.nic.club',
  live: 'whois.nic.live',
  cloud: 'whois.nic.cloud',

  // Country Code TLDs
  kr: 'whois.kr',
  jp: 'whois.jprs.jp',
  cn: 'whois.cnnic.cn',
  uk: 'whois.nic.uk',
  de: 'whois.denic.de',
  fr: 'whois.nic.fr',
  it: 'whois.nic.it',
  es: 'whois.nic.es',
  nl: 'whois.domain-registry.nl',
  ru: 'whois.tcinet.ru',
  ca: 'whois.cira.ca',
  in: 'whois.registry.in',
  mx: 'whois.mx',
  cv: 'whois.nic.cv',
  au: 'whois.auda.org.au',
  br: 'whois.registro.br',

  // ccSLDs
  'it.com': 'whois.centralnic.com',
  'uk.com': 'whois.centralnic.com',
  'us.com': 'whois.centralnic.com',
  'eu.com': 'whois.centralnic.com',
  'co.kr': 'whois.kr',
  'or.kr': 'whois.kr',
  'co.uk': 'whois.nic.uk',
  'org.uk': 'whois.nic.uk',
  'com.au': 'whois.auda.org.au',
};

function getWhoisServer(domain: string): string {
  const parts = domain.toLowerCase().split('.');

  // Check ccSLD first (e.g., co.kr, it.com)
  if (parts.length >= 3) {
    const ccSLD = parts.slice(-2).join('.');
    if (WHOIS_SERVERS[ccSLD]) {
      return WHOIS_SERVERS[ccSLD];
    }
  }

  // Then check TLD
  const tld = parts[parts.length - 1];
  return WHOIS_SERVERS[tld] || 'whois.iana.org';
}

function queryWhois(server: string, domain: string): Promise<string> {
  return new Promise((resolve, reject) => {
    const chunks: Buffer[] = [];

    // Special query formats for some servers
    let query = domain;
    if (server.includes('verisign')) {
      query = '=' + domain;
    } else if (server.includes('denic.de')) {
      query = '-T dn,ace ' + domain;
    } else if (server.includes('jprs.jp')) {
      query = domain + '/e';
    }

    const socket = createConnection(43, server, () => {
      socket.write(query + '\r\n');
    });

    socket.setTimeout(15000);

    socket.on('data', (data) => {
      chunks.push(data);
    });

    socket.on('end', () => {
      resolve(Buffer.concat(chunks).toString('utf-8'));
    });

    socket.on('timeout', () => {
      socket.destroy();
      reject(new Error('Connection timeout'));
    });

    socket.on('error', (err) => {
      reject(err);
    });
  });
}

function extractReferral(raw: string): string | null {
  const patterns = [
    /Registrar WHOIS Server:\s*(.+)/i,
    /Whois Server:\s*(.+)/i,
    /ReferralServer:\s*whois:\/\/(.+)/i,
    /refer:\s*(.+)/i,
  ];

  for (const pattern of patterns) {
    const match = raw.match(pattern);
    if (match && match[1]) {
      const server = match[1].trim().replace('whois://', '');
      if (server && !server.includes(' ')) {
        return server;
      }
    }
  }
  return null;
}

function checkAvailability(raw: string): boolean {
  const availablePatterns = [
    'no match for',
    'not found',
    'no data found',
    'domain not found',
    'no entries found',
    'status: available',
    'the queried object does not exist',
    'is available for registration',
    'this domain name has not been registered',
  ];

  const rawLower = raw.toLowerCase();
  return availablePatterns.some(p => rawLower.includes(p));
}

export default async function handler(req: VercelRequest, res: VercelResponse) {
  // CORS
  res.setHeader('Access-Control-Allow-Origin', '*');
  res.setHeader('Access-Control-Allow-Methods', 'GET, OPTIONS');
  res.setHeader('Access-Control-Allow-Headers', 'X-API-Key, Content-Type');

  if (req.method === 'OPTIONS') {
    return res.status(200).end();
  }

  // API Key check (optional)
  const apiKey = process.env.API_KEY;
  if (apiKey && req.headers['x-api-key'] !== apiKey) {
    return res.status(401).json({ error: 'Invalid API key' });
  }

  const { domain } = req.query;

  if (!domain || typeof domain !== 'string') {
    return res.status(400).json({ error: 'Domain parameter required' });
  }

  const domainName = domain.toLowerCase().trim();
  const startTime = Date.now();

  try {
    const whoisServer = getWhoisServer(domainName);
    let raw = await queryWhois(whoisServer, domainName);
    let usedServer = whoisServer;

    // Follow referral if exists
    const referral = extractReferral(raw);
    if (referral && referral !== whoisServer) {
      try {
        const referralRaw = await queryWhois(referral, domainName);
        if (referralRaw.length > raw.length / 2) {
          raw = referralRaw;
          usedServer = referral;
        }
      } catch {
        // Keep original response if referral fails
      }
    }

    const available = checkAvailability(raw);
    const queryTime = Date.now() - startTime;

    return res.status(200).json({
      domain: domainName,
      available,
      whois_server: usedServer,
      raw,
      query_time_ms: queryTime,
    });

  } catch (error) {
    const queryTime = Date.now() - startTime;
    return res.status(500).json({
      domain: domainName,
      error: error instanceof Error ? error.message : 'Unknown error',
      query_time_ms: queryTime,
    });
  }
}