Walker_Nav_Menu Add Strings and Class Name

This drove me crazy. Here is the solution, hope someone find it useful or suggest a better and shorter solution:

class sstmyp_Walker_Nav_Menu extends Walker_Nav_Menu {

    function display_element($element, &$children_elements, $max_depth, $depth=0, $args, &$output) {

        $id_field = $this->db_fields['id'];

        // add custom class and carets to menu has children
        if(in_array("menu-item-has-children", $element->classes)) {
            $element->classes[] = 'dropdown';
            $element->title .= ' <i class="fa fa-angle-down"></i>';
        }

        // add class active
        if(in_array("current-menu-item", $element->classes)) {
            $element->classes[] = 'active';
        }

        parent::display_element($element, $children_elements, $max_depth, $depth, $args, $output);
    }       

    function start_lvl(&$output, $depth = 1, $args = Array() ) {
        $indent = str_repeat("\t", $depth);
        $output .= "\n$indent<ul class=\"dropdown-menu\">\n"; 
    }

    public function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
        $indent = ( $depth ) ? str_repeat( "\t", $depth ) : '';

        $classes = empty( $item->classes ) ? array() : (array) $item->classes;
        $classes[] = 'menu-item-' . $item->ID;

        $class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item, $args, $depth ) );
        $class_names = $class_names ? ' class="' . esc_attr( $class_names ) . '"' : '';

        $id = apply_filters( 'nav_menu_item_id', 'menu-item-'. $item->ID, $item, $args, $depth );
        $id = $id ? ' id="' . esc_attr( $id ) . '"' : '';

        $output .= $indent . '<li' . $id . $class_names .'>';

        $atts = array();
        $atts['title']  = ! empty( $item->attr_title ) ? $item->attr_title : '';
        $atts['target'] = ! empty( $item->target )     ? $item->target     : '';
        $atts['rel']    = ! empty( $item->xfn )        ? $item->xfn        : '';
        $atts['href']   = ! empty( $item->url )        ? $item->url        : '';
        //add attribute
        if(in_array("dropdown-toggle", $classes)) {
            $atts['data-toggle'] = "dropdown";
            $atts['class'] = "dropdown-toggle";
        }
        $atts = apply_filters( 'nav_menu_link_attributes', $atts, $item, $args, $depth );

        $attributes="";
        foreach ( $atts as $attr => $value ) {
            if ( ! empty( $value ) ) {
                $value = ( 'href' === $attr ) ? esc_url( $value ) : esc_attr( $value );
                $attributes .= ' ' . $attr . '="' . $value . '"';
            }
        }

        $item_output = $args->before;
        $item_output .= '<a'. $attributes .'>';
         // This filter is documented in wp-includes/post-template.php
        $item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;
        $item_output .= '</a>';
        $item_output .= $args->after;
        $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
    }       

}