import { createReadStream } from 'node:fs';
import { stat } from 'node:fs/promises';
import path from 'node:path';

const MIME = {
  '.html': 'text/html; charset=utf-8',
  '.css': 'text/css; charset=utf-8',
  '.js': 'text/javascript; charset=utf-8',
  '.json': 'application/json; charset=utf-8',
  '.svg': 'image/svg+xml',
  '.png': 'image/png',
  '.jpg': 'image/jpeg',
  '.webp': 'image/webp',
  '.ico': 'image/x-icon',
  '.woff2': 'font/woff2',
  '.txt': 'text/plain; charset=utf-8',
};

/**
 * Resolve a URL pathname to a file inside `root`, or null if it escapes it.
 * Exported for tests.
 */
export function resolveSafe(root, pathname) {
  let decoded;
  try {
    decoded = decodeURIComponent(pathname);
  } catch {
    return null;
  }
  if (decoded.includes('\0')) return null;
  const target = path.resolve(root, '.' + path.posix.normalize('/' + decoded));
  return target === root || target.startsWith(root + path.sep) ? target : null;
}

/** Serve files from `root`. Revalidates with ETag so edits show up on refresh. */
export function createStaticHandler(root) {
  const base = path.resolve(root);

  return async function serve(req, res, pathname, headers) {
    let file = resolveSafe(base, pathname === '/' ? '/index.html' : pathname);
    if (!file) return send(res, 400, headers, 'Bad request');

    let info;
    try {
      info = await stat(file);
      if (info.isDirectory()) {
        file = path.join(file, 'index.html');
        info = await stat(file);
      }
    } catch {
      return send(res, 404, headers, 'Not found');
    }

    const etag = `W/"${info.size.toString(16)}-${Math.floor(info.mtimeMs).toString(16)}"`;
    const type = MIME[path.extname(file).toLowerCase()] ?? 'application/octet-stream';
    const out = { ...headers, 'Content-Type': type, 'Cache-Control': 'no-cache', ETag: etag };

    if (req.headers['if-none-match'] === etag) {
      res.writeHead(304, out);
      return res.end();
    }
    res.writeHead(200, { ...out, 'Content-Length': info.size });
    if (req.method === 'HEAD') return res.end();
    createReadStream(file).on('error', () => res.destroy()).pipe(res);
  };
}

function send(res, status, headers, text) {
  res.writeHead(status, { ...headers, 'Content-Type': 'text/plain; charset=utf-8' });
  res.end(text);
}