proxy.js

import { createI18nMiddleware } from 'fumadocs-core/i18n/middleware';
import { isMarkdownPreferred } from 'fumadocs-core/negotiation';
import { NextResponse } from 'next/server';
import { i18n } from './lib/i18n';

const handleI18n = createI18nMiddleware(i18n);
const INTERNAL_PREFIXES = ['/_next', '/api'];
const MARKDOWN_SUFFIX_RE = /\.(md|mdx)$/i;
const STATIC_FILE_RE = /\.[^/]+$/;

function getLocaleFromPath(pathname) {
  const segment = pathname.split('/')[1];
  return i18n.languages.includes(segment) ? segment : null;
}

function isStaticAsset(pathname) {
  if (pathname === '/llms.txt' || pathname === '/llms-full.txt') {
    return false;
  }

  return STATIC_FILE_RE.test(pathname) && !MARKDOWN_SUFFIX_RE.test(pathname);
}

function stripLocale(pathname, lang) {
  const prefix = `/${lang}`;
  const stripped = pathname === prefix ? '/' : pathname.slice(prefix.length) || '/';
  return stripped.startsWith('/') ? stripped : `/${stripped}`;
}

function toMarkdownPath(pathname, lang) {
  const localizedPath = stripLocale(pathname, lang).replace(/\/$/, '');
  return localizedPath && localizedPath !== '/'
    ? `/${lang}/llms.mdx${localizedPath}/content.md`
    : `/${lang}/llms.mdx/content.md`;
}

function isInternalRoute(pathname) {
  return INTERNAL_PREFIXES.some((prefix) => pathname === prefix || pathname.startsWith(`${prefix}/`));
}

// Build the options object for NextResponse.next() that injects x-current-path
// into the request headers, so server components (e.g. app/[lang]/(docs)/layout.jsx)
// can read the request pathname and filter the sidebar page tree by active edition.
// Next.js does not expose pathname to server components without this kind of header
// injection.
function withPathHeader(request) {
  const headers = new Headers(request.headers);
  headers.set('x-current-path', request.nextUrl.pathname);
  return { request: { headers } };
}

export default function proxy(request) {
  const { pathname } = request.nextUrl;

  if (isInternalRoute(pathname) || isStaticAsset(pathname)) {
    return NextResponse.next();
  }

  const lang = getLocaleFromPath(pathname);
  if (!lang) {
    return handleI18n(request);
  }

  if (
    pathname === `/${lang}/llms.txt`
    || pathname === `/${lang}/llms-full.txt`
    || pathname.startsWith(`/${lang}/llms.mdx/`)
  ) {
    return NextResponse.next(withPathHeader(request));
  }

  if (MARKDOWN_SUFFIX_RE.test(pathname)) {
    const cleanPath = pathname.replace(MARKDOWN_SUFFIX_RE, '') || `/${lang}`;
    return NextResponse.rewrite(new URL(toMarkdownPath(cleanPath, lang), request.nextUrl));
  }

  if (isMarkdownPreferred(request)) {
    return NextResponse.rewrite(new URL(toMarkdownPath(pathname, lang), request.nextUrl));
  }

  return NextResponse.next(withPathHeader(request));
}