import net from 'node:net';

// 协议族识别只用于生成「SSH 响应正常」这类摘要；版本号等细节默认不回显，避免写入公开的 status.json
const FAMILIES = [
  { re: /^SSH-\d/i, name: 'SSH' },
  { re: /^220[\s\S]*ESMTP/i, name: 'SMTP' },
  { re: /^220[\s\S]*FTP/i, name: 'FTP' },
  { re: /^\+OK/i, name: 'POP3' },
  { re: /^\* OK/i, name: 'IMAP' },
  { re: /^HTTP\/\d/i, name: 'HTTP' },
  { re: /^220\b/i, name: 'SMTP/TCP' },
];

/**
 * 被动 banner 探测：连接后仅读取服务端主动发送的标识串（RFC 4253 的 SSH banner 即此类），
 * 不做认证、不发送任何数据、不执行任何命令——因此不会触发目标侧的登录失败计数或封禁。
 * 需要客户端先发字节的协议（Redis/MySQL）不适用，属于路线图内容。
 */
export function probeBanner(monitor) {
  const started = Date.now();
  const timeoutMs = (monitor.timeout ?? 10) * 1000;
  const maxBytes = Math.max(32, Number(monitor.maxBannerBytes) || 512);
  return new Promise((resolve) => {
    const socket = net.createConnection({ host: monitor.host, port: monitor.port });
    let raw = '';
    let settled = false;

    const done = (status, detail) => {
      if (settled) return;
      settled = true;
      socket.destroy();
      resolve({ status, latency: Date.now() - started, code: null, detail });
    };

    const evaluate = () => {
      const line = (raw.split(/\r?\n/)[0] ?? '').trim();
      const family = FAMILIES.find((f) => f.re.test(line))?.name ?? null;
      if (monitor.expectBanner) {
        let ok = false;
        try {
          ok = new RegExp(monitor.expectBanner, monitor.bannerFlags || 'i').test(line);
        } catch {
          return done('down', 'banner 规则无法编译（expectBanner 不是合法正则）');
        }
        // 不匹配时只报告策略结果，不回显实际收到的标识串
        if (!ok) return done('down', '标识串与期望规则不符');
      }
      const label = family ? `${family} 响应正常` : '收到服务标识串';
      return done('up', monitor.revealBanner ? `${label}：${line.slice(0, 80)}` : label);
    };

    socket.setTimeout(timeoutMs, () => done('down', '等待标识串超时'));
    socket.once('error', (err) =>
      done('down', err.code === 'ECONNREFUSED' ? '连接被拒绝（端口关闭）' : (err.code || err.message))
    );
    // 对端发完就断开（无换行结尾）也算有效响应
    socket.once('end', () => (raw ? evaluate() : done('down', '连接被对端关闭且未发送标识串')));
    // 只在收到换行或达到字节上限时判定，避免把分包到达的标识串截断
    socket.on('data', (chunk) => {
      raw += chunk.toString('latin1');
      if (/[\r\n]/.test(raw) || raw.length >= maxBytes) evaluate();
    });
  });
}