Bootstrap Wordpress Nav Walker, changes markup on your menus to use bootstrap formatting

bootstrap-walker.php

<?php class responsive_menu_walker extends Walker_Nav_Menu
	{
		function start_lvl(&$output, $depth) {
			// update the <li> element
			$bookmark = 'den-menu-top';
			$li_pos = strrpos ( $output, $bookmark );
			$output = substr($output, 0, $li_pos+strlen($bookmark)) . " dropdown" . substr($output, $li_pos+strlen($bookmark), strlen($output) - $li_pos);
			
			// update the <a> element
			$bookmark = "<a ";
			$anchor_pos = strrpos ( $output, $bookmark );

			$output = substr($output, 0, $anchor_pos+strlen($bookmark)) . substr($output, $anchor_pos+strlen($bookmark), strlen($output) - $anchor_pos);
			
			$output .= "<span class=\"disclosure-down\"></span><ul class=\"dropdown-menu sub-menu sub-menu-". $depth ."\">";
		}
		function end_lvl(&$output, $depth) {
			$output .= "</ul>";
		}
		
	    function start_el(&$output, $item, $depth, $args)
	    {
	           global $wp_query;
	           $indent = ( $depth ) ? str_repeat( "\t", $depth ) : '';

	           $class_names = $value = '';

	           $classes = empty( $item->classes ) ? array() : (array) $item->classes;

			   $page_info = get_page($item->object_id); // get the page slug

			   $page_slug = $page_info->post_name;

	           $class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item ) );

				
				if ( $item->menu_item_parent == 0  ? $parent_item = ' den-menu-top' : $parent_item = '' );
				
	           $class_names = ' class="'. esc_attr( $class_names ) . ' nb-' . $page_slug . $parent_item . '"';
				
	           $output .= $indent . '<li id="menu-item-'. $item->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        ) .'"' : '';
				
			   $prepend = '';
	           $append = '';
	           $description  = ! empty( $item->description ) ? ' <span>'.esc_attr( $item->description ).'</span>' : '';

	           if($depth != 0)
	           {
					$description = $append = $prepend = "";
	           }
				
	            $item_output = $args->before;
	            $item_output .= '<a'. $attributes .'>';
	            $item_output .= $args->link_before .$prepend.apply_filters( 'the_title', $item->title, $item->ID ).$append;
	            $item_output .= $description.$args->link_after;
	            $item_output .= '</a>';
	            $item_output .= $args->after;

	            $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
			}
	} ?>