related post

Hello guys, i have one problem and i want your help.
I have that code:

//------------------------------------------------------
	//  Related Posts
	//------------------------------------------------------
	if(!function_exists('cherry_related_posts')){
		function cherry_related_posts($args = array()){
			global $post;
			$default = array(
				'post_type' => get_post_type($post),
				'class' => 'related-posts',
				'class_list' => 'related-posts_list',
				'class_list_item' => 'related-posts_item',
				'display_title' => true,
				'display_link' => true,
				'display_thumbnail' => true,
				'width_thumbnail' => 170,
				'height_thumbnail' => 170,
				'before_title' => '<h3 class="related-posts_h">',
				'after_title' => '</h3>',
				'posts_count' => 4
			);
			extract(array_merge($default, $args));

			$post_tags = wp_get_post_terms($post->ID, $post_type.'_tag', array("fields" => "slugs"));
			$tags_type = $post_type=='post' ? 'tag' : $post_type.'_tag' ;
			$suppress_filters = get_option('suppress_filters');// WPML filter
			$blog_related = apply_filters( 'cherry_text_translate', of_get_option('blog_related'), 'blog_related' );
			if ($post_tags && !is_wp_error($post_tags)) {
				$args = array(
					"$tags_type" => implode(',', $post_tags),
					'post_status' => 'publish',
					'posts_per_page' => $posts_count,
					'ignore_sticky_posts' => 1,
					'post__not_in' => array($post->ID),
					'post_type' => $post_type,
					'suppress_filters' => $suppress_filters
					);
				query_posts($args);
				if ( have_posts() ) {
					$output = '<div class="'.$class.'">';
					$output .= $display_title ? $before_title.$blog_related.$after_title : '' ;
					$output .= '<ul class="'.$class_list.' clearfix">';
					while( have_posts() ) {
						the_post();
						$thumb   = has_post_thumbnail() ? get_post_thumbnail_id() : PARENT_URL.'/images/empty_thumb.gif';
						$blank_img = stripos($thumb, 'empty_thumb.gif');
						$img_url = $blank_img ? $thumb : wp_get_attachment_url( $thumb,'full');
						$image   = $blank_img ? $thumb : aq_resize($img_url, $width_thumbnail, $height_thumbnail, true) or $img_url;

						$output .= '<li class="'.$class_list_item.'">';
						$output .= $display_thumbnail ? '<figure class="thumbnail featured-thumbnail"><a href="'.get_permalink().'" title="'.get_the_title().'"><img data-src="'.$image.'" alt="'.get_the_title().'" /></a></figure>': '' ;
						$output .= $display_link ? '<a href="'.get_permalink().'" >'.get_the_title().'</a>': '' ;
						$output .= '</li>';
					}
					$output .= '</ul></div>';
					echo $output;
				}
				wp_reset_query();
			}
		}
	}

That code is for related post in my blog, but works with TAGS, i want to change that and i make it to works with CATEGORIES, can you help me please? thank you!