Example of adding an option to a WooCommerce attribute

attribute-filter-option.php

<?php
if ( ! defined( 'ABSPATH' ) ) exit; // Exit if accessed directly


add_action( 'woocommerce_after_edit_attribute_fields', 'blz_attr_filter_option', 50 );
add_action( 'woocommerce_after_add_attribute_fields', 'blz_attr_filter_option', 50 );
add_action( 'admin_init' , 'blz_attr_save', 99 );

/**
 * Display the populated checkbox for the Create Filter Widget option
 *
 * @return void
 */
function blz_attr_filter_option(){
    $attribute_filter_widget = false;
    if( isset( $_GET['edit'] ) ){
        $attr_id = $_GET['edit'];
        global $wpdb;
        $attribute_to_edit = $wpdb->get_row(
            $wpdb->prepare(
                "
                SELECT attribute_type, attribute_label, attribute_name, attribute_orderby, attribute_public
                FROM {$wpdb->prefix}woocommerce_attribute_taxonomies WHERE attribute_id = %d
                ",
                $attr_id
            )
        );
        $attribute_name = $attribute_to_edit->attribute_name;
        $attribute_filter_widget = get_option( 'attribute_filter_widget_' . $attribute_name );
    }
    ?>
    <tr>
        <th scope="row" valign="top">
            <label for="attribute_filter_widget"><?php esc_html_e( 'Create Filter Widget', 'blz' ); ?></label>
        </th>
        <td>
            <input name="attribute_filter_widget" id="attribute_filter_widget" type="checkbox" value="1" <?php checked( $attribute_filter_widget, 1 ); ?> />
            <p class="description"><?php esc_html_e( 'Enable this if you want to create a filter widget on the category page.', 'blz' ); ?></p>

        </td>
    </tr>
    <?php
}

/**
 * Save the Filter Widget option
 */
function blz_attr_save(  ){
    if( isset( $_POST['attribute_name'] ) && isset( $_POST['save_attribute'] ) && $_POST['save_attribute'] == 'Update' ){
        // Update existing attribute
        $attribute_filter_widget = isset($_POST['attribute_filter_widget']) ? wc_clean( wp_unslash( $_POST['attribute_filter_widget'] ) ) : '';
        $attribute_name = wc_clean( wp_unslash( $_POST['attribute_name'] ) );
        $success = update_option( 'attribute_filter_widget_' . $attribute_name, $attribute_filter_widget );
        return;
    }
    if ( isset( $_POST['add_new_attribute']) && $_POST['add_new_attribute'] == 'Add attribute' ){
        // Add new attribute
        $attribute_filter_widget = isset($_POST['attribute_filter_widget']) ? wc_clean( wp_unslash( $_POST['attribute_filter_widget'] ) ) : '';
        if( isset( $_POST['attribute_name'] ) && ! empty( $_POST['attribute_name'] ) ){
            $attribute_name = wc_clean( wp_unslash( $_POST['attribute_name'] ) );
            $success = update_option( 'attribute_filter_widget_' . $attribute_name, $attribute_filter_widget );
        } elseif ( isset( $_POST['attribute_label'] ) && ! empty( $_POST['attribute_label'] ) ){
            $label = wc_clean( wp_unslash( $_POST['attribute_label'] ) );
            $attribute_name = sanitize_title_with_dashes( $label ); // Likely, not guaranteed to be correct.
            $success = update_option( 'attribute_filter_widget_' . $attribute_name, $attribute_filter_widget );
        }
    }
}