<?php
/**
 * Custom Walker for Nav Menu Editor
 *
 */
class MegaMenu_Walker_Edit extends Walker_Nav_Menu_Edit {
    /**
     * Start the element output.
     *
     * We're injecting our custom fields after the div.submitbox
     *
     * @see Walker_Nav_Menu::start_el()
     * @since 0.1.0
     * @since 0.2.0 Update regex pattern to support WordPress 4.7's markup.
     *
     * @param string $output Passed by reference. Used to append additional content.
     * @param object $item   Menu item data object.
     * @param int    $depth  Depth of menu item. Used for padding.
     * @param array  $args   Menu item args.
     * @param int    $id     Nav menu ID.
     */
    function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
        $item_output = '';
        parent::start_el( $item_output, $item, $depth, $args, $id );
        $output .= preg_replace(
            // NOTE: Check this regex from time to time!
            '/(?=<(fieldset|p)[^>]+class="[^"]*field-move)/',
            $this->get_fields( $item, $depth, $args ),
            $item_output
        );
    }
    /**
     * Get custom fields
     *
     * @access protected
     * @since 0.1.0
     * @uses add_action() Calls 'menu_item_custom_fields' hook
     *
     * @param object $item   Menu item data object.
     * @param int    $depth  Depth of menu item. Used for padding.
     * @param array  $args   Menu item args.
     * @param int    $id     Nav menu ID.
     *
     * @return string Form fields
     */
    protected function get_fields( $item, $depth, $args = array(), $id = 0 ) {
        global $wp_version;
        if ( version_compare( $wp_version, '5.4', '<=' ) ) {
            ob_start();
            /**
             * Get menu item custom fields from plugins/themes
             *
             * @since 0.1.0
             * @since 1.0.0 Pass correct parameters.
             *
             * @param int    $item_id  Menu item ID.
             * @param object $item     Menu item data object.
             * @param int    $depth    Depth of menu item. Used for padding.
             * @param array  $args     Menu item args.
             * @param int    $id       Nav menu ID.
             *
             * @return string Custom fields HTML.
             */
            do_action( 'wp_nav_menu_item_custom_fields', $item->ID, $item, $depth, $args, $id );
            return ob_get_clean();
        }

    }
}