feat: Add comprehensive SEO implementation

- Add robots.txt with admin/API blocking
- Add dynamic sitemap.xml with static pages and genre pages
- Implement full meta tags (Open Graph, Twitter Cards, Canonical, Alternates)
- Add SEO helper functions for domain detection and URL generation
- Add generateMetadata to all pages (homepage, about, genre, special)
- Support automatic domain detection for hoerdle.de and hördle.de
- Add SEO configuration to lib/config.ts

app/[locale]/[genre]/page.tsx

@@ -6,6 +6,8 @@ import { PrismaClient } from '@prisma/client';
 import { notFound } from 'next/navigation';
 import { getLocalizedValue } from '@/lib/i18n';
 import { getTranslations } from 'next-intl/server';
+import { generateBaseMetadata } from '@/lib/metadata';
+import type { Metadata } from 'next';
 
 export const dynamic = 'force-dynamic';
 
@@ -15,6 +17,32 @@ interface PageProps {
     params: Promise<{ locale: string; genre: string }>;
 }
 
+export async function generateMetadata({ params }: PageProps): Promise<Metadata> {
+    const { locale, genre } = await params;
+    const decodedGenre = decodeURIComponent(genre);
+    
+    // Fetch genre to get localized name
+    const allGenres = await prisma.genre.findMany();
+    const currentGenre = allGenres.find(g => getLocalizedValue(g.name, locale) === decodedGenre);
+    
+    if (!currentGenre || !currentGenre.active) {
+        return await generateBaseMetadata(locale, genre);
+    }
+    
+    const genreName = getLocalizedValue(currentGenre.name, locale);
+    const genreSubtitle = getLocalizedValue(currentGenre.subtitle, locale);
+    
+    const title = locale === 'de'
+        ? `${genreName} - Hördle`
+        : `${genreName} - Hördle`;
+    
+    const description = genreSubtitle || (locale === 'de'
+        ? `Spiele Hördle im Genre ${genreName} und errate Songs aus kurzen Audio-Clips!`
+        : `Play Hördle in the ${genreName} genre and guess songs from short audio clips!`);
+    
+    return await generateBaseMetadata(locale, genre, title, description);
+}
+
 export default async function GenrePage({ params }: PageProps) {
     const { locale, genre } = await params;
     const decodedGenre = decodeURIComponent(genre);

app/[locale]/about/page.tsx

@@ -1,10 +1,22 @@
 import { getTranslations } from "next-intl/server";
 import { Link } from "@/lib/navigation";
+import { generateBaseMetadata } from "@/lib/metadata";
+import type { Metadata } from "next";
 
 interface AboutPageProps {
   params: Promise<{ locale: string }>;
 }
 
+export async function generateMetadata({ params }: AboutPageProps): Promise<Metadata> {
+  const { locale } = await params;
+  const t = await getTranslations({ locale, namespace: "About" });
+  
+  const title = t("title");
+  const description = t("intro");
+  
+  return await generateBaseMetadata(locale, "about", title, description);
+}
+
 export default async function AboutPage({ params }: AboutPageProps) {
   const { locale } = await params;
   const t = await getTranslations({ locale, namespace: "About" });

app/[locale]/layout.tsx

@@ -8,6 +8,7 @@ import { notFound } from 'next/navigation';
 import { headers } from 'next/headers';
 
 import { config } from "@/lib/config";
+import { generateBaseMetadata } from "@/lib/metadata";
 import InstallPrompt from "@/components/InstallPrompt";
 import AppFooter from "@/components/AppFooter";
 
@@ -21,10 +22,10 @@ const geistMono = Geist_Mono({
     subsets: ["latin"],
 });
 
-export const metadata: Metadata = {
-    title: config.appName,
-    description: config.appDescription,
-};
+export async function generateMetadata({ params }: { params: Promise<{ locale: string }> }): Promise<Metadata> {
+    const { locale } = await params;
+    return await generateBaseMetadata(locale);
+}
 
 export const viewport: Viewport = {
     themeColor: config.colors.themeColor,

app/[locale]/page.tsx

@@ -7,15 +7,33 @@ import { Link } from '@/lib/navigation';
 import { PrismaClient } from '@prisma/client';
 import { getTranslations } from 'next-intl/server';
 import { getLocalizedValue } from '@/lib/i18n';
+import { generateBaseMetadata } from '@/lib/metadata';
+import type { Metadata } from 'next';
 
 export const dynamic = 'force-dynamic';
 
 const prisma = new PrismaClient();
 
+export async function generateMetadata({ params }: { params: Promise<{ locale: string }> }): Promise<Metadata> {
+    const { locale } = await params;
+    const t = await getTranslations('Home');
+    
+    // Get localized title and description
+    const title = locale === 'de' 
+        ? 'Hördle - Tägliches Musik-Erraten'
+        : 'Hördle - Daily Music Guessing Game';
+    
+    const description = locale === 'de'
+        ? 'Spiele Hördle und errate Songs aus kurzen Audio-Clips! Täglich neue Rätsel aus verschiedenen Genres. Inspiriert von Wordle, aber für Musikfans.'
+        : 'Play Hördle and guess songs from short audio clips! Daily new puzzles from various genres. Inspired by Wordle, but for music lovers.';
+    
+    return await generateBaseMetadata(locale, '', title, description);
+}
+
 export default async function Home({
     params
 }: {
-    params: { locale: string };
+    params: Promise<{ locale: string }>;
 }) {
     const { locale } = await params;
     const t = await getTranslations('Home');

app/[locale]/special/[name]/page.tsx

@@ -5,6 +5,8 @@ import { Link } from '@/lib/navigation';
 import { PrismaClient } from '@prisma/client';
 import { getLocalizedValue } from '@/lib/i18n';
 import { getTranslations } from 'next-intl/server';
+import { generateBaseMetadata } from '@/lib/metadata';
+import type { Metadata } from 'next';
 
 export const dynamic = 'force-dynamic';
 
@@ -14,6 +16,30 @@ interface PageProps {
     params: Promise<{ locale: string; name: string }>;
 }
 
+export async function generateMetadata({ params }: PageProps): Promise<Metadata> {
+    const { locale, name } = await params;
+    const decodedName = decodeURIComponent(name);
+    
+    // Fetch special to get localized name
+    const allSpecials = await prisma.special.findMany();
+    const currentSpecial = allSpecials.find(s => getLocalizedValue(s.name, locale) === decodedName);
+    
+    if (!currentSpecial) {
+        return await generateBaseMetadata(locale, `special/${name}`);
+    }
+    
+    const specialName = getLocalizedValue(currentSpecial.name, locale);
+    const specialSubtitle = getLocalizedValue(currentSpecial.subtitle, locale);
+    
+    const title = `★ ${specialName} - Hördle`;
+    
+    const description = specialSubtitle || (locale === 'de'
+        ? `Spiele das Hördle-Special "${specialName}" und errate Songs aus kurzen Audio-Clips!`
+        : `Play the Hördle special "${specialName}" and guess songs from short audio clips!`);
+    
+    return await generateBaseMetadata(locale, `special/${name}`, title, description);
+}
+
 export default async function SpecialPage({ params }: PageProps) {
     const { locale, name } = await params;
     const decodedName = decodeURIComponent(name);

app/robots.ts

@@ -0,0 +1,20 @@
+import { MetadataRoute } from 'next';
+import { config } from '@/lib/config';
+
+export default function robots(): MetadataRoute.Robots {
+    const baseUrl = process.env.NEXT_PUBLIC_DOMAIN || config.domain;
+    const protocol = process.env.NODE_ENV === 'production' ? 'https' : 'http';
+    const siteUrl = `${protocol}://${baseUrl}`;
+
+    return {
+        rules: [
+            {
+                userAgent: '*',
+                allow: '/',
+                disallow: ['/admin/', '/api/'],
+            },
+        ],
+        sitemap: `${siteUrl}/sitemap.xml`,
+    };
+}
+

app/sitemap.ts

@@ -0,0 +1,128 @@
+import { MetadataRoute } from 'next';
+import { PrismaClient } from '@prisma/client';
+import { getLocalizedValue } from '@/lib/i18n';
+import { config } from '@/lib/config';
+
+const prisma = new PrismaClient();
+
+export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
+    const baseUrl = process.env.NEXT_PUBLIC_DOMAIN || config.domain;
+    const protocol = process.env.NODE_ENV === 'production' ? 'https' : 'http';
+    const siteUrl = `${protocol}://${baseUrl}`;
+
+    const now = new Date().toISOString();
+
+    // Static pages
+    const staticPages: MetadataRoute.Sitemap = [
+        {
+            url: `${siteUrl}/en`,
+            lastModified: now,
+            changeFrequency: 'daily',
+            priority: 1.0,
+            alternates: {
+                languages: {
+                    'de': `${siteUrl}/de`,
+                    'en': `${siteUrl}/en`,
+                    'x-default': `${siteUrl}/en`,
+                },
+            },
+        },
+        {
+            url: `${siteUrl}/de`,
+            lastModified: now,
+            changeFrequency: 'monthly',
+            priority: 0.8,
+            alternates: {
+                languages: {
+                    'de': `${siteUrl}/de`,
+                    'en': `${siteUrl}/en`,
+                    'x-default': `${siteUrl}/en`,
+                },
+            },
+        },
+        {
+            url: `${siteUrl}/en/about`,
+            lastModified: now,
+            changeFrequency: 'monthly',
+            priority: 0.7,
+            alternates: {
+                languages: {
+                    'de': `${siteUrl}/de/about`,
+                    'en': `${siteUrl}/en/about`,
+                    'x-default': `${siteUrl}/en/about`,
+                },
+            },
+        },
+        {
+            url: `${siteUrl}/de/about`,
+            lastModified: now,
+            changeFrequency: 'monthly',
+            priority: 0.7,
+            alternates: {
+                languages: {
+                    'de': `${siteUrl}/de/about`,
+                    'en': `${siteUrl}/en/about`,
+                    'x-default': `${siteUrl}/en/about`,
+                },
+            },
+        },
+    ];
+
+    // Dynamic genre pages
+    try {
+        const genres = await prisma.genre.findMany({
+            where: { active: true },
+        });
+
+        const genrePages: MetadataRoute.Sitemap = [];
+
+        for (const genre of genres) {
+            const genreNameEn = getLocalizedValue(genre.name, 'en');
+            const genreNameDe = getLocalizedValue(genre.name, 'de');
+
+            // Only add if genre name is valid
+            if (genreNameEn && genreNameDe) {
+                const encodedEn = encodeURIComponent(genreNameEn);
+                const encodedDe = encodeURIComponent(genreNameDe);
+
+                genrePages.push(
+                    {
+                        url: `${siteUrl}/en/${encodedEn}`,
+                        lastModified: now,
+                        changeFrequency: 'daily',
+                        priority: 0.9,
+                        alternates: {
+                            languages: {
+                                'de': `${siteUrl}/de/${encodedDe}`,
+                                'en': `${siteUrl}/en/${encodedEn}`,
+                                'x-default': `${siteUrl}/en/${encodedEn}`,
+                            },
+                        },
+                    },
+                    {
+                        url: `${siteUrl}/de/${encodedDe}`,
+                        lastModified: now,
+                        changeFrequency: 'daily',
+                        priority: 0.9,
+                        alternates: {
+                            languages: {
+                                'de': `${siteUrl}/de/${encodedDe}`,
+                                'en': `${siteUrl}/en/${encodedEn}`,
+                                'x-default': `${siteUrl}/en/${encodedEn}`,
+                            },
+                        },
+                    }
+                );
+            }
+        }
+
+        return [...staticPages, ...genrePages];
+    } catch (error) {
+        console.error('Error generating sitemap:', error);
+        // Return static pages only if database query fails
+        return staticPages;
+    } finally {
+        await prisma.$disconnect();
+    }
+}
+

lib/config.ts

@@ -12,5 +12,9 @@ export const config = {
         text: process.env.NEXT_PUBLIC_CREDITS_TEXT || 'Vibe coded with ☕ and 🍺 by',
         linkText: process.env.NEXT_PUBLIC_CREDITS_LINK_TEXT || '@elpatron@digitalcourage.social',
         linkUrl: process.env.NEXT_PUBLIC_CREDITS_LINK_URL || 'https://digitalcourage.social/@elpatron',
+    },
+    seo: {
+        ogImage: process.env.NEXT_PUBLIC_OG_IMAGE || '/favicon.ico',
+        twitterHandle: process.env.NEXT_PUBLIC_TWITTER_HANDLE || undefined,
     }
 };

lib/metadata.ts

@@ -0,0 +1,64 @@
+import type { Metadata } from 'next';
+import { config } from './config';
+import { getBaseUrl } from './seo';
+
+/**
+ * Generate base metadata with Open Graph, Twitter Cards, and canonical URLs
+ */
+export async function generateBaseMetadata(
+    locale: string,
+    path: string = '',
+    title?: string,
+    description?: string,
+    image?: string
+): Promise<Metadata> {
+    const baseUrl = await getBaseUrl();
+    const pathSegment = path ? `/${path}` : '';
+    const fullUrl = `${baseUrl}/${locale}${pathSegment}`;
+    
+    // Determine alternate URLs for both locales (same path for both)
+    const alternateLocale = locale === 'de' ? 'en' : 'de';
+    const alternateUrl = `${baseUrl}/${alternateLocale}${pathSegment}`;
+    
+    // Default values
+    const metaTitle = title || config.appName;
+    const metaDescription = description || config.appDescription;
+    const ogImage = image || `${baseUrl}${config.seo.ogImage}`;
+    
+    return {
+        title: metaTitle,
+        description: metaDescription,
+        alternates: {
+            canonical: fullUrl,
+            languages: {
+                [locale]: fullUrl,
+                [alternateLocale]: alternateUrl,
+                'x-default': `${baseUrl}/en${pathSegment}`,
+            },
+        },
+        openGraph: {
+            title: metaTitle,
+            description: metaDescription,
+            url: fullUrl,
+            siteName: config.appName,
+            images: [
+                {
+                    url: ogImage,
+                    width: 1200,
+                    height: 630,
+                    alt: metaTitle,
+                },
+            ],
+            locale: locale,
+            type: 'website',
+        },
+        twitter: {
+            card: 'summary_large_image',
+            title: metaTitle,
+            description: metaDescription,
+            images: [ogImage],
+            ...(config.seo.twitterHandle && { creator: config.seo.twitterHandle }),
+        },
+    };
+}
+

lib/seo.ts

@@ -0,0 +1,43 @@
+import { headers } from 'next/headers';
+import { config } from './config';
+
+/**
+ * Get the current base URL from request headers
+ * Automatically detects hoerdle.de or hördle.de (xn--hrdle-jua.de)
+ */
+export async function getBaseUrl(): Promise<string> {
+    const headersList = await headers();
+    const host = headersList.get('host') || headersList.get('x-forwarded-host') || '';
+    
+    let domain = config.domain; // Default fallback
+    
+    if (host) {
+        // Extract domain from host (remove port if present)
+        const detectedDomain = host.split(':')[0].toLowerCase();
+        
+        // Map domains
+        if (detectedDomain === 'hoerdle.de') {
+            domain = 'hoerdle.de';
+        } else if (detectedDomain === 'hördle.de' || detectedDomain === 'xn--hrdle-jua.de') {
+            domain = 'hördle.de';
+        } else {
+            // Use detected domain if it's different from default
+            domain = detectedDomain;
+        }
+    }
+    
+    // Always use HTTPS in production
+    const protocol = process.env.NODE_ENV === 'production' ? 'https' : 'http';
+    return `${protocol}://${domain}`;
+}
+
+/**
+ * Get base URL synchronously (for use in non-async contexts)
+ * Uses environment variable or config as fallback
+ */
+export function getBaseUrlSync(): string {
+    const domain = process.env.NEXT_PUBLIC_DOMAIN || config.domain;
+    const protocol = process.env.NODE_ENV === 'production' ? 'https' : 'http';
+    return `${protocol}://${domain}`;
+}
+