WordPress Custom Walker: Split menu based on item count

mbt_split_nav_walker.php

/* ========================================================================== 
    Custom Walker Menu
   ========================================================================== */

class mbt_split_nav_walker extends Walker_Nav_Menu {

    var $current_menu = null;
    var $break_point  = null;

    function start_el(&$output, $item, $depth, $args) {

        global $wp_query;

            // Get the locations of nav menus
            $theme_locations = get_nav_menu_locations();
         
            // Get the menu object of the current nav menu based on the returned theme location
            $menu_obj = get_term( $theme_locations[$args->theme_location], 'nav_menu' );


            if( !isset( $this->current_menu ) ) {
                $this->current_menu = wp_get_nav_menu_object( $menu_obj->term_id );
            }
            if( !isset( $this->break_point ) ) {
                $this->break_point = ceil( $this->current_menu->count / 2 ) + 1; 
            }  


        $indent = ( $depth ) ? str_repeat( "\t", $depth ) : '';

        $class_names = $value = '';

        $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 ) );
        $class_names = ' class="' . esc_attr( $class_names ) . '"';

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

        if( $this->break_point == $item->menu_order ) {
            $output .= $indent . '</li></span></ul><ul class="nav top-nav cf right"><span><li' . $id . $value . $class_names .'>';
        } else {
            $output .= $indent . '<li' . $id . $value . $class_names . '>';
        }

        $attributes  = ! empty( $item->attr_title ) ? ' title="'  . esc_attr( $item->attr_title ) .'"' : '';
        $attributes .= ! empty( $item->target )     ? ' target="' . esc_attr( $item->target     ) .'"' : '';
        $attributes .= ! empty( $item->xfn )        ? ' rel="'    . esc_attr( $item->xfn        ) .'"' : '';
        $attributes .= ! empty( $item->url )        ? ' href="'   . esc_attr( $item->url        ) .'"' : '';

        $item_output = $args->before;
        $item_output .= '<a'. $attributes .'>';
        $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 );
    }
}