simple related posts plugin

function plugin_basic_related(){
	$categories = get_the_category();
	$current = get_the_ID();

	$search = array();

	foreach($categories as $category){
		$search[] = $category->term_id;
	}

	$args = array(
		'post_type' => 'post',
		'category__in' => $search,
		'post__not_in' => array($current),
		'posts_per_page' => 3
	);

	$posts = new WP_Query( $args );

	$return = '<h4>Related Posts</h4>
		<div class="related-posts">';

	foreach($posts->posts as $post){
		$id = $post->ID;
		$thumbnail = get_the_post_thumbnail_url($id);
		$title = $post->post_title;
		$link = get_permalink($id);

		$return .= '<div class="related-item">
			<a href="' . $link . '">
				<div class="background" style="background-image: url(' . $thumbnail . ')"></div>
				<div class="title">
					<p><span>' . $title . '</span></p>
				</div>
			</a>
		</div>';

	}

	$return .= '</div>';

	echo $return;

} add_shortcode('basic_related', 'plugin_basic_related');