複数言語のサイトマップインデックスの作成

// app/sitemap.xml/route.ts
import { locales, siteBaseUrl } from '@/i18n-config';

export async function GET() {
  const sitemapIndex = `<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex xmlns="[http://www.sitemaps.org/schemas/sitemap/0.9](http://www.sitemaps.org/schemas/sitemap/0.9)">
  ${locales
    .map((locale) => {
      return `
    <sitemap>
      <loc>${siteBaseUrl}/sitemap-${locale}.xml</loc>
      <lastmod>${new Date().toISOString()}</lastmod>
    </sitemap>`;
    })
    .join('')}
</sitemapindex>
`;

  return new Response(sitemapIndex, {
    headers: {
      'Content-Type': 'application/xml',
    },
  });
}

// app/sitemap-[lang].xml/route.ts
import { locales, siteBaseUrl } from '@/i18n-config';

// This tells Next.js which sitemaps to build at build time
export async function generateStaticParams() {
  return locales.map((lang) => ({
    lang,
  }));
}

// A helper function to get all pages for a language
// In a real app, this would fetch from a CMS or database
async function getPagesForLanguage(lang: string): Promise<string[]> {
  // These are relative paths, *without* the lang prefix
  // e.g., '/', '/about', '/blog/my-post'
  return ['/', '/about', '/contact'];
}

export async function GET(
  request: Request,
  { params }: { params: { lang: string } }
) {
  const { lang } = params;

  if (!locales.includes(lang)) {
    return new Response('Not Found', { status: 404 });
  }

  const pages = await getPagesForLanguage(lang);

  const sitemap = `<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="[http://www.sitemaps.org/schemas/sitemap/0.9](http://www.sitemaps.org/schemas/sitemap/0.9)">
  ${pages
    .map((page) => {
      const path = page === '/' ? '' : page;
      return `
    <url>
      <loc>${siteBaseUrl}/${lang}${path}</loc>
      <lastmod>${new Date().toISOString()}</lastmod>
    </url>`;
    })
    .join('')}
</urlset>
`;

  return new Response(sitemap, {
    headers: {
      'Content-Type': 'application/xml',
    },
  });
}