【WordPress】テーマにJSON-LD形式の構造化データを追加する方法

<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "Article",
  "headline": "記事タイトル",
  "image": "アイキャッチ画像のURL",
  "author": {
    "@type": "Person",
    "name": "著者名"
  },
  "datePublished": "公開日",
  "dateModified": "更新日",
  "mainEntityOfPage": {
    "@type": "WebPage",
    "@id": "記事のURL"
  }
}
</script>

function add_json_ld_article() {
  if (is_single()) {
    global $post;
    $title = get_the_title($post);
    $url = get_permalink($post);
    $author = get_the_author_meta('display_name', $post->post_author);
    $published = get_the_date('c', $post);
    $modified = get_the_modified_date('c', $post);
    $image = get_the_post_thumbnail_url($post->ID, 'full');

    $data = array(
      "@context" => "https://schema.org",
      "@type" => "Article",
      "headline" => $title,
      "author" => array(
        "@type" => "Person",
        "name" => $author
      ),
      "datePublished" => $published,
      "dateModified" => $modified,
      "mainEntityOfPage" => array(
        "@type" => "WebPage",
        "@id" => $url
      )
    );

    // アイキャッチ画像がある場合のみimageプロパティを追加
    if ($image) {
      $data["image"] = $image;
    }

    echo '<script type="application/ld+json">' . PHP_EOL;
    // JSON_UNESCAPED_SLASHESは付けない（scriptタグの抜け出し対策のため / は \/ にエスケープする）
    echo json_encode($data, JSON_UNESCAPED_UNICODE | JSON_PRETTY_PRINT);
    echo PHP_EOL . '</script>' . PHP_EOL;
  }
}
add_action('wp_head', 'add_json_ld_article');