Category & Tag Description Shortcode

// Shortcode fpr Category & Tag Desc
add_shortcode('cat_desc', 'cat_desc_shortcode');
function cat_desc_shortcode( $atts, $content = null ) {
    $a = shortcode_atts( array(
        'id' => null,
        'slug' => null,
        'title' => 'false',
        'link' => 'true',
    ), $atts );

    if( $a['id'] ) {
        $cat = get_category( $a['id'] );
        $a['title'] = 'true';
    } elseif( $a['slug'] ) {
        $cat = get_category_by_slug( $a['slug'] );
        $a['title'] = 'true';
    } else {
        $cat = get_the_category()[0];
    }

    if( $cat == null ) return;

    $cat->url = get_category_link( $cat->term_id );


    $output .= '<div class="description">'.$cat->description.'</div>';
    return $output;
}