<?php

/**
 * Add a parent class for menu item
 */
function add_menu_parent_class( $items ) {

	$parents = array();
	foreach ( $items as $item ) {
		if ( $item->menu_item_parent && $item->menu_item_parent > 0 ) {
			$parents[] = $item->menu_item_parent;
		}
	}

	foreach ( $items as $item ) {
		if ( in_array( $item->ID, $parents ) ) {
			$item->classes[] = 'has-dropdown';
		}
	}

	return $items;
}
add_filter( 'wp_nav_menu_objects', 'add_menu_parent_class' );
/**
 * Add a class to sub menu
 */
class Sub_Menu extends Walker_Nav_Menu {
	// add classes to ul sub-menus
	function start_lvl( &$output, $depth ) {
		$indent        = ( $depth > 0  ? str_repeat( "\t", $depth ) : '' );
		$display_depth = ( $depth + 1);
		$class_names   = 'dropdown';
		$output       .= "\n" . $indent . '<ul class="' . $class_names . '">' . "\n";
	}
}
/**
 * Remove extraneous WordPress classes & id's
 */
function my_css_attributes_filter($var) {
  return is_array($var) ? array_intersect($var, array('current-menu-item', 'has-dropdown', 'logged-in')) : '';
}
add_filter('nav_menu_css_class', 'my_css_attributes_filter', 100, 1);
add_filter('nav_menu_item_id', 'my_css_attributes_filter', 100, 1);
add_filter('page_css_class', 'my_css_attributes_filter', 100, 1);