'use strict';

const http = require('http');

const PORT = Number(process.env.PORT) || 3000;
const VM_DOCS_BASE_URL = (process.env.VM_DOCS_BASE_URL || '').replace(/\/+$/, '');

const STAND_RE = /^[A-Za-z0-9._-]+$/;

function send(res, status, body, headers = {}) {
  const data = Buffer.from(String(body));
  res.writeHead(status, {
    'Content-Type': 'text/plain; charset=utf-8',
    'Content-Length': data.length,
    ...headers,
  });
  res.end(data);
}

function redirect(res, location) {
  send(res, 302, '', { Location: location });
}

const server = http.createServer((req, res) => {
  if (req.method !== 'GET' && req.method !== 'HEAD') {
    send(res, 405, 'Method Not Allowed');
    return;
  }

  let pathname;
  try {
    pathname = decodeURIComponent(req.url.split('?')[0]);
  } catch (err) {
    send(res, 400, 'Bad Request');
    return;
  }

  if (pathname === '/health') {
    send(res, 200, 'ok');
    return;
  }

  if (pathname === '/') {
    if (!VM_DOCS_BASE_URL) {
      send(res, 500, 'VM_DOCS_BASE_URL is not configured');
      return;
    }
    redirect(res, VM_DOCS_BASE_URL + '/');
    return;
  }

  if (!VM_DOCS_BASE_URL) {
    send(res, 500, 'VM_DOCS_BASE_URL is not configured');
    return;
  }

  const segments = pathname.split('/').filter((s) => s !== '');
  if (segments.some((s) => s === '..')) {
    send(res, 400, 'Bad Request');
    return;
  }

  const stand = segments[0];
  if (!stand || !STAND_RE.test(stand)) {
    send(res, 404, 'Not Found');
    return;
  }

  redirect(res, VM_DOCS_BASE_URL + pathname);
});

if (require.main === module) {
  server.listen(PORT, () => {
    console.log(`redirect router listening on :${PORT}`);
    console.log(`VM_DOCS_BASE_URL=${VM_DOCS_BASE_URL || '(not set)'}`);
  });
}

module.exports = { server, send, redirect };