// 自动提取文章第一张图片作为特色图片
function nirvana_auto_featured_image($content) {
    global $post;
    if (has_post_thumbnail($post->ID)) {
        return $content;
    }
    if (preg_match('/<img[^>]+src=["\']([^"\']+)["\']/i', $content, $matches)) {
        $image_url = $matches[1];
        $image_id = attachment_url_to_postid($image_url);
        if ($image_id) {
            set_post_thumbnail($post->ID, $image_id);
        }
    }
    return $content;
}
add_filter('the_content', 'nirvana_auto_featured_image', 5);

// 添加默认特色图片功能
function nirvana_default_featured_image($html, $post_id, $post_thumbnail_id, $size, $attr) {
    if (empty($html)) {
        $default_image = get_template_directory_uri() . '/assets/imgs/default-header.svg';
        $html = '<img src="' . $default_image . '" alt="Default Featured Image" class="wp-post-image" />';
    }
    return $html;
}
add_filter('post_thumbnail_html', 'nirvana_default_featured_image', 10, 5);

// 修改 get_post_thumbnail_id 返回值，当没有特色图片时返回默认值
function nirvana_default_featured_image_id($thumbnail_id, $post_id) {
    if (empty($thumbnail_id)) {
        // 返回一个虚拟 ID，让 post_thumbnail_html 过滤器处理
        return null;
    }
    return $thumbnail_id;
}
add_filter('get_post_thumbnail_id', 'nirvana_default_featured_image_id', 10, 2);

// 修改 get_post_meta 返回，当日志头图为空时返回默认图片
function nirvana_default_head_img($value, $post_id, $meta_key, $single) {
    if ($meta_key === '日志头图' && empty($value)) {
        return get_template_directory_uri() . '/assets/imgs/default-header.svg';
    }
    return $value;
}
add_filter('get_post_metadata', 'nirvana_default_head_img', 10, 4);