import { createServer } from "node:http";
import { readFile, stat } from "node:fs/promises";
import { resolve, sep } from "node:path";

const types = { ".html": "text/html; charset=utf-8", ".css": "text/css; charset=utf-8", ".js": "text/javascript; charset=utf-8", ".svg": "image/svg+xml", ".md": "text/plain; charset=utf-8", ".json": "application/json; charset=utf-8" };

/** Loopback-only static server, explicitly scoped to the supplied directory roots. */
export async function serve(root, { port = 0, mounts = {} } = {}) {
  root = resolve(root);
  const server = createServer(async (req, res) => {
    try {
      const path = decodeURIComponent(new URL(req.url, "http://localhost").pathname);
      const mount = Object.keys(mounts).find(prefix => path.startsWith(prefix));
      const base = mount ? resolve(mounts[mount]) : root;
      let file = resolve(base, `.${mount ? path.slice(mount.length - 1) : path}`);
      if (file !== base && !file.startsWith(base + sep)) throw new Error("Outside served directory");
      if ((await stat(file)).isDirectory()) file = resolve(file, "index.html");
      const body = await readFile(file);
      const ext = /\.[^.]+$/.exec(file)?.[0];
      res.writeHead(200, { "content-type": types[ext] ?? "application/octet-stream", "cache-control": "no-store" });
      res.end(body);
    } catch {
      res.writeHead(404); res.end("Not found");
    }
  });
  await new Promise((done, reject) => { server.once("error", reject); server.listen(port, "127.0.0.1", done); });
  return { server, url: `http://127.0.0.1:${server.address().port}/`, close: () => new Promise(done => server.close(done)) };
}