/**
 * Dependency-free local development server for XZBT.
 *
 * It deliberately binds only to loopback. It is not part of the distributed
 * XZBT artifact and cannot establish direct-file Phase 0 feasibility results.
 */
import { createReadStream, statSync } from 'node:fs';
import { createServer } from 'node:http';
import { extname, normalize, resolve, sep } from 'node:path';
import { fileURLToPath } from 'node:url';

const root = resolve(fileURLToPath(new URL('..', import.meta.url)));
const host = '127.0.0.1';
const loopbackAddresses = ['127.0.0.1', '::1'];
const port = Number.parseInt(process.env.XZBT_DEV_PORT ?? '5173', 10);

if (!Number.isInteger(port) || port < 1 || port > 65535) {
  throw new Error('XZBT_DEV_PORT must be an integer from 1 through 65535.');
}

const mimeTypes = new Map([
  ['.css', 'text/css; charset=utf-8'],
  ['.html', 'text/html; charset=utf-8'],
  ['.js', 'text/javascript; charset=utf-8'],
  ['.json', 'application/json; charset=utf-8'],
  ['.mjs', 'text/javascript; charset=utf-8'],
  ['.xzbt', 'application/json; charset=utf-8'],
]);

function requestedPath(requestUrl) {
  const pathname = new URL(requestUrl, `http://${host}:${port}`).pathname;
  const decodedPath = decodeURIComponent(pathname);
  if (decodedPath.includes('\0')) return null;
  if (decodedPath.split('/').some((segment) => segment.startsWith('.'))) return null;

  const relativePath = decodedPath === '/'
    ? 'prototypes/phase0/XZBT-phase0-probe.html'
    : decodedPath.replace(/^\/+/, '');
  const candidate = resolve(root, normalize(relativePath));
  return candidate === root || candidate.startsWith(`${root}${sep}`) ? candidate : null;
}

function handleRequest(request, response) {
  if (!['GET', 'HEAD'].includes(request.method ?? '')) {
    response.writeHead(405, { Allow: 'GET, HEAD' }).end();
    return;
  }

  let path;
  try {
    path = requestedPath(request.url ?? '/');
  } catch {
    response.writeHead(400).end('Malformed request path.');
    return;
  }
  if (!path) {
    response.writeHead(403).end('Path is outside the XZBT workspace.');
    return;
  }

  let stats;
  try {
    stats = statSync(path);
  } catch {
    response.writeHead(404).end('Not found.');
    return;
  }
  if (!stats.isFile()) {
    response.writeHead(404).end('Not found.');
    return;
  }

  response.writeHead(200, {
    'Content-Length': stats.size,
    'Content-Type': mimeTypes.get(extname(path).toLowerCase()) ?? 'application/octet-stream',
    'Cache-Control': 'no-store',
    'X-Content-Type-Options': 'nosniff',
  });
  if (request.method === 'HEAD') response.end();
  else createReadStream(path).pipe(response);
}

for (const address of loopbackAddresses) {
  const server = createServer(handleRequest);
  server.listen(port, address, () => {
    console.log(`XZBT development server: http://${address}:${port}/`);
  });
}
console.log(`Serving workspace root: ${root}`);