Next.js SEO best practices: server-side rendering and meta tags

import { generateLocaleMetadata, getCanonicalUrl } from '@saas/i18n';
import { localeMetadata, routing } from '@/i18n/routing';
import type { Metadata } from 'next';

export async function generateMetadata({
  params,
}: {
  params: Promise<{ locale: string }>;
}): Promise<Metadata> {
  const { locale: localeParam } = await params;
  const locale = routing.locales.includes(localeParam as any)
    ? localeParam
    : routing.defaultLocale;
  const baseUrl = process.env.NEXT_PUBLIC_APP_URL || 'https://example.com';
  const pathname = '/';

  return generateLocaleMetadata(
    pathname,
    baseUrl,
    locale,
    routing,
    localeMetadata,
    {
      title: 'Fastack Boilerplate - Modern SaaS Starter Template',
      description: 'A production-ready SaaS boilerplate built with Next.js, TypeScript, and modern best practices. Get started building your SaaS faster.',
      keywords: ['SaaS', 'boilerplate', 'Next.js', 'TypeScript', 'starter', 'template', 'fastack', 'React'],
      authors: [{ name: 'Fastack Boilerplate' }],
      openGraph: {
        title: 'Fastack Boilerplate - Modern SaaS Starter Template',
        description: 'A production-ready SaaS boilerplate built with Next.js, TypeScript, and modern best practices.',
        type: 'website',
        siteName: 'Fastack Boilerplate',
      },
      twitter: {
        card: 'summary_large_image',
        title: 'Fastack Boilerplate - Modern SaaS Starter Template',
        description: 'A production-ready SaaS boilerplate built with Next.js, TypeScript, and modern best practices.',
      },
      alternates: {
        canonical: getCanonicalUrl(pathname, baseUrl, routing, locale),
      },
      manifest: '/manifest.json',
      other: {
        'mobile-web-app-capable': 'yes',
        'apple-mobile-web-app-capable': 'yes',
        'apple-mobile-web-app-status-bar-style': 'default',
      },
    }
  );
}

export function generateLocaleMetadata<Locale extends string>(
  pathname: string,
  baseUrl: string,
  locale: Locale,
  routing: RoutingConfig<Locale>,
  localeMetadata: Record<Locale, LocaleMetadata>,
  additionalMetadata?: Metadata
): Metadata {
  const validLocale = routing.locales.includes(locale)
    ? locale
    : routing.defaultLocale;
  const metadata = localeMetadata[validLocale];

  if (!metadata) {
    throw new Error(`Locale metadata not found for locale: ${locale}. Please ensure the locale is defined in localeMetadata.`);
  }

  const otherMetadata: Record<string, string> = {
    ...(additionalMetadata?.other as Record<string, string> | undefined),
    'og:locale': metadata.code,
    'og:locale:alternate': routing.locales
      .filter((l) => l !== validLocale)
      .map((l) => localeMetadata[l]?.code)
      .filter(Boolean)
      .join(', '),
  };

  return {
    ...additionalMetadata,
    alternates: {
      ...additionalMetadata?.alternates,
      languages: generateAlternateLanguages(pathname, baseUrl, routing),
    },
    other: otherMetadata,
  };
}

export function getCanonicalUrl<Locale extends string>(
  pathname: string,
  baseUrl: string,
  routing: RoutingConfig<Locale>,
  locale?: Locale
): string {
  const targetLocale = locale || routing.defaultLocale;

  if (targetLocale === routing.defaultLocale) {
    return `${baseUrl}${pathname}`;
  }

  return `${baseUrl}/${targetLocale}${pathname}`;
}

import { MetadataRoute } from 'next';
import { routing } from '@/i18n/routing';

export default function sitemap(): MetadataRoute.Sitemap {
  const baseUrl = process.env.NEXT_PUBLIC_APP_URL || 'https://example.com';

  const routes = [
    '',
    '/pricing',
    '/privacy-policy',
    '/terms-of-service',
    '/contact',
    '/cookie-policy',
    '/auth'
  ];

  const sitemapEntries: MetadataRoute.Sitemap = [];

  routing.locales.forEach((locale) => {
    routes.forEach((route) => {
      const url = locale === routing.defaultLocale
        ? `${baseUrl}${route}`
        : `${baseUrl}/${locale}${route}`;

      sitemapEntries.push({
        url,
        lastModified: new Date(),
        changeFrequency: route === '' ? 'weekly' : 'monthly',
        priority: route === '' ? 1 : 0.7,
      });
    });
  });

  return sitemapEntries;
}