function generateJsonLd(site, seo, req) {
  const siteUrl = site.url || 'https://pengzhan.dev';
  const person = {
    '@type': 'Person',
    '@id': `${siteUrl}/#person`,
    name: (site.author && site.author.name) || site.title,
    url: siteUrl,
    jobTitle: (site.author && site.author.subtitle) || 'Software Engineer',
    sameAs: (site.social || []).map(s => s.url).filter(Boolean)
  };

  const website = {
    '@type': 'WebSite',
    '@id': `${siteUrl}/#website`,
    url: siteUrl,
    name: site.title,
    description: site.tagline,
    publisher: { '@id': `${siteUrl}/#person` },
    potentialAction: [
      {
        '@type': 'SearchAction',
        target: {
          '@type': 'EntryPoint',
          urlTemplate: `${siteUrl}/search?q={search_term_string}`
        },
        'query-input': 'required name=search_term_string'
      }
    ]
  };

  const graph = [person, website];

  if (seo.type === 'article') {
    const blogPosting = {
      '@type': 'BlogPosting',
      '@id': `${seo.canonicalUrl}#article`,
      isPartOf: { '@id': `${siteUrl}/#website` },
      author: { '@id': `${siteUrl}/#person` },
      headline: seo.title,
      datePublished: seo.publishedTime || new Date().toISOString(),
      dateModified: seo.modifiedTime || seo.publishedTime || new Date().toISOString(),
      mainEntityOfPage: seo.canonicalUrl,
      description: seo.description,
      image: seo.ogImage,
      articleSection: seo.category || 'Tech',
      keywords: Array.isArray(seo.tags) ? seo.tags.join(', ') : seo.tags
    };
    graph.push(blogPosting);
  }

  // Breadcrumbs
  const breadcrumbItems = [
    {
      '@type': 'ListItem',
      position: 1,
      name: 'Home',
      item: siteUrl
    }
  ];

  if (req.path !== '/') {
    breadcrumbItems.push({
      '@type': 'ListItem',
      position: 2,
      name: seo.title,
      item: seo.canonicalUrl
    });
  }

  graph.push({
    '@type': 'BreadcrumbList',
    '@id': `${seo.canonicalUrl}#breadcrumb`,
    itemListElement: breadcrumbItems
  });

  return JSON.stringify({
    '@context': 'https://schema.org',
    '@graph': graph
  });
}

function seoMiddleware(siteConfig) {
  return (req, res, next) => {
    res.locals.site = siteConfig.site;
    res.locals.navigation = siteConfig.navigation;
    res.locals.social = siteConfig.social;
    res.locals.currentPath = req.path;

    // Helper to generate SEO metadata
    res.locals.seo = {
      title: siteConfig.site.title,
      description: siteConfig.site.tagline,
      canonicalUrl: `${siteConfig.site.url}${req.path}`,
      ogImage: `${siteConfig.site.url}/images/og-default.png`,
      type: 'website',
      tags: [],
      category: ''
    };

    res.locals.getJsonLd = () => generateJsonLd(siteConfig.site, res.locals.seo, req);

    next();
  };
}

module.exports = seoMiddleware;