/**
     * Render the sub-menu page for 'CSV Export'
     *
     * @since 3.0
     */
    public function render_submenu_pages()
    {
        // permissions check
        if (!current_user_can('manage_woocommerce')) {
            return;
        }
        $this->tabs = array('export' => __('Export', WC_Customer_Order_CSV_Export::TEXT_DOMAIN), 'settings' => __('Settings', WC_Customer_Order_CSV_Export::TEXT_DOMAIN));
        $current_tab = empty($_GET['tab']) ? 'export' : urldecode($_GET['tab']);
        // settings
        if (!empty($_POST) && 'settings' == $current_tab) {
            // security check
            if (!wp_verify_nonce($_POST['_wpnonce'], __FILE__)) {
                wp_die(__('Action failed. Please refresh the page and retry.', WC_Customer_Order_CSV_Export::TEXT_DOMAIN));
            }
            if (isset($_POST['wc_customer_order_csv_export_test_method'])) {
                // process test
                $export = new WC_Customer_Order_CSV_Export_Handler(0);
                $result = $export->test_export_via($_POST['wc_customer_order_csv_export_test_method']);
                $this->message_handler->add_message($result);
            } else {
                $orig_start_inverval = get_option('wc_customer_order_csv_export_auto_export_start_time') . get_option('wc_customer_order_csv_export_auto_export_interval');
                // save settings
                woocommerce_update_options($this->get_settings('settings'));
                // clear scheduled export event if export interval and/or start time were changed
                if ($orig_start_inverval !== get_option('wc_customer_order_csv_export_auto_export_start_time') . get_option('wc_customer_order_csv_export_auto_export_interval')) {
                    // note this resets the next scheduled execution time to the time options were saved + the interval
                    wp_clear_scheduled_hook('wc_customer_order_csv_export_auto_export_orders');
                }
                $this->message_handler->add_message(__('Your settings have been saved.', WC_Customer_Order_CSV_Export::TEXT_DOMAIN));
            }
        }
        ?>
		<div class="wrap woocommerce">
		<form method="post" id="mainform" action="" enctype="multipart/form-data">
			<h2 class="nav-tab-wrapper woo-nav-tab-wrapper">
				<?php 
        foreach ($this->tabs as $tab_id => $tab_title) {
            $class = $tab_id == $current_tab ? array('nav-tab', 'nav-tab-active') : array('nav-tab');
            $url = add_query_arg('tab', $tab_id, admin_url('admin.php?page=wc_customer_order_csv_export'));
            printf('<a href="%s" class="%s">%s</a>', esc_url($url), implode(' ', array_map('sanitize_html_class', $class)), esc_html($tab_title));
        }
        ?>
 </h2> <?php 
        $this->message_handler->show_messages();
        if ('settings' == $current_tab) {
            $this->render_settings_page();
        } else {
            $this->render_export_page();
        }
        ?>
 </form>
		</div> <?php 
    }