/**
 * Prometheus HTTP server.
 *
 * One `node:http` listener, a map-based router for page routes, and a tiny
 * static-file handler for /static/*. No framework, no templating engine —
 * the response-rendering path for a page is: look up the handler, call it,
 * wrap the result in `layout()`, flush. If any step of that stops reading
 * at a glance, we have gotten too clever.
 *
 * Dynamic routes land here later: /api/upload, /api/manifest, /api/publish,
 * /api/pay, /admin/*. For now the server is only serving pages, so the
 * router is only pages.
 */

import { createServer } from 'node:http';
import { readFile } from 'node:fs/promises';
import { createReadStream, statSync } from 'node:fs';
import { fileURLToPath } from 'node:url';
import { dirname, join, normalize, resolve } from 'node:path';
import { layout } from './layout.js';
import * as pages from './pages.js';

const PORT = Number(process.env.PORT) || 3700;
const BIND = process.env.BIND || '127.0.0.1';

const SELF = fileURLToPath(import.meta.url);
const SERVICE_DIR = dirname(SELF);
const PUBLIC_DIR = resolve(SERVICE_DIR, '..', 'public');

/**
 * The page router.
 *
 * Exact-match paths first. Patterns (category pages, listing detail) will
 * attach here when the browse milestone lands.
 */
const PAGE_ROUTES = {
  '/':            pages.home,
  '/publish':     pages.publish,
  '/browse':      pages.browse,
  '/submit':      pages.submit,
  '/boundaries':  pages.boundaries,
};

/**
 * Content types for static files. Deliberately short — if the server
 * learns to serve a type that is not here, add it here rather than
 * reaching for `mime-types`.
 */
const MIME = {
  '.css':  'text/css; charset=utf-8',
  '.svg':  'image/svg+xml',
  '.js':   'text/javascript; charset=utf-8',
  '.png':  'image/png',
  '.ico':  'image/x-icon',
  '.woff2': 'font/woff2',
  '.txt':  'text/plain; charset=utf-8',
};

/* ============ server ============ */

const server = createServer(async (req, res) => {
  const started = Date.now();
  const url = normalizeRequestUrl(req.url);

  try {
    if (url.startsWith('/static/')) {
      await serveStatic(url.slice('/static/'.length), res);
    } else if (PAGE_ROUTES[url]) {
      servePage(PAGE_ROUTES[url], res);
    } else {
      servePage(pages.notFound, res, 404, req);
    }
  } catch (err) {
    // The response-level error log is intentionally short — a stack trace
    // in the terminal is for the operator, not every reader.
    console.error('[prometheus] 500', req.method, url, err?.message || err);
    if (!res.headersSent) {
      res.writeHead(500, { 'content-type': 'text/plain; charset=utf-8' });
    }
    res.end('internal error\n');
  }

  res.on('close', () => {
    const ms = Date.now() - started;
    console.log(`[prometheus] ${res.statusCode} ${req.method} ${url} ${ms}ms`);
  });
});

server.listen(PORT, BIND, () => {
  console.log(`[prometheus] listening on http://${BIND}:${PORT}`);
});

/* ============ helpers ============ */

/**
 * Trim query/hash, decode once, collapse any `..` to its parent.
 * Returns a leading-slash path.
 */
function normalizeRequestUrl(raw) {
  const [path] = String(raw || '/').split('?');
  const decoded = decodeURIComponent(path);
  // normalize + leading-slash enforcement means `/foo/..//bar` → `/bar`.
  // On Windows, node:path/normalize uses backslashes; convert back.
  const normalized = normalize(decoded).replaceAll('\\', '/');
  return normalized.startsWith('/') ? normalized : '/' + normalized;
}

/**
 * Render a page function to the response.
 */
function servePage(fn, res, status = 200, req = null) {
  const page = fn(req);
  const html = layout(page);
  res.writeHead(status, {
    'content-type': 'text/html; charset=utf-8',
    'cache-control': 'public, max-age=60',
  });
  res.end(html);
}

/**
 * Serve a file from PUBLIC_DIR by relative path. The caller passes a
 * path with no leading slash and no `..`; this double-checks via
 * path.resolve against PUBLIC_DIR and refuses anything that escapes.
 */
async function serveStatic(relPath, res) {
  const full = resolve(PUBLIC_DIR, relPath);
  if (!full.startsWith(PUBLIC_DIR + '\\') && !full.startsWith(PUBLIC_DIR + '/')) {
    res.writeHead(400, { 'content-type': 'text/plain' });
    res.end('bad path\n');
    return;
  }

  let st;
  try {
    st = statSync(full);
  } catch {
    res.writeHead(404, { 'content-type': 'text/plain' });
    res.end('not found\n');
    return;
  }
  if (!st.isFile()) {
    res.writeHead(404, { 'content-type': 'text/plain' });
    res.end('not found\n');
    return;
  }

  const ext = '.' + relPath.split('.').pop();
  const mime = MIME[ext] || 'application/octet-stream';
  res.writeHead(200, {
    'content-type': mime,
    // Static assets are versioned in the URL (`?v=1`), so a long cache is
    // safe and the only way to make the viewport snappy on repeat visits.
    'cache-control': 'public, max-age=31536000, immutable',
    'content-length': st.size,
  });
  createReadStream(full).pipe(res);
}