Easiest way to double the rate in certain cases?

Hey there!

I want to add checkbox to the checkout page where customers can also order return pickup for the items. And if they check that, the kilometers rate should be doubled.

I already have working code to double the basic WooCommerce fees via ajax etc, but how can I attach myself into this plugin and update it’s rate too?

Example of code I’m already using to double the basic shipping costs:

// Add a Custom checkbox field for shipping options (just for testing)
add_action( 'woocommerce_after_checkout_billing_form', 'custom_billing_checkbox_for_testing', 10, 1 );
function custom_billing_checkbox_for_testing( $checkout ) {
    $field_id = 'billing_ups_yn';

    // Get the checked state if exist
    $billing_ups = WC()->session->get('billing_ups' );
    if(empty($billing_ups))
        $billing_ups = $checkout->get_value( $field_id );

    // Add the custom checkout field (checkbox)
    woocommerce_form_field( $field_id, array(
        'type' => 'checkbox',
        'class' => array( 'form-row-wide' ),
        'label' => __('DOUBLE THE SHIPPING COSTS'),
    ), $billing_ups );
}

// function that gets the Ajax data
add_action( 'wp_ajax_woo_get_ajax_data', 'woo_get_ajax_data' );
add_action( 'wp_ajax_nopriv_woo_get_ajax_data', 'woo_get_ajax_data' );
function woo_get_ajax_data() {
    if ( $_POST['billing_ups'] == '1' ){
        WC()->session->set('billing_ups', '1' );
    } else {
        WC()->session->set('billing_ups', '0' );
    }
    echo json_encode( WC()->session->get('billing_ups' ) );
    die(); // Alway at the end (to avoid server error 500)
}

// Conditionally changing the shipping methods costs
add_filter( 'woocommerce_package_rates','conditional_custom_shipping_cost', 90, 2 );
function conditional_custom_shipping_cost( $rates, $package ) {

    if ( WC()->session->get('billing_ups' ) == '1' ){
        foreach ( $rates as $rate_key => $rate_values ) {
            // Not for "Free Shipping method" (all others only)
            if ( 'free_shipping' !== $rate_values->method_id ) {

                // Set the rate cost
                $rates[$rate_key]->cost = $rates[$rate_key]->cost * 2;

                // Set taxes rate cost (if enabled)
                $taxes = array();
                foreach ($rates[$rate_key]->taxes as $key => $tax)
                    if( $rates[$rate_key]->taxes[$key] > 0 ) // set the new tax cost
                        $taxes[$key] = $taxes[$key] * 2;
                $rates[$rate_key]->taxes = $taxes;
            }
        }
    }
    return $rates;
}

// Enabling, disabling and refreshing session shipping methods data
add_action( 'woocommerce_checkout_update_order_review', 'refresh_shipping_methods', 10, 1 );
function refresh_shipping_methods( $post_data ){
    $bool = true;
    if ( WC()->session->get('billing_ups' ) == '1' ) $bool = false;

    // Mandatory to make it work with shipping methods
    foreach ( WC()->cart->get_shipping_packages() as $package_key => $package ){
        WC()->session->set( 'shipping_for_package_' . $package_key, $bool );
    }
    WC()->cart->calculate_shipping();
}

// The Jquery script
add_action( 'wp_footer', 'custom_checkout_script' );
function custom_checkout_script() {
    ?>
    <script type="text/javascript">
        jQuery( function($){

            // update cart on delivery location checkbox option
            $('#billing_ups_yn_field input').change( function () {
                var checked = 0;
                if ( $('#billing_ups_yn').is(':checked') )
                    checked = 1;

                $.ajax({
                    type: 'POST',
                    url: wc_checkout_params.ajax_url,
                    data: {
                        'action': 'woo_get_ajax_data',
                        'billing_ups': checked,
                    },
                    success: function (result) {
                        $('body').trigger('update_checkout');
                        console.log('response: '+result); // just for testing
                    },
                    error: function(error){
                        console.log(error); // just for testing
                    }
                });
            });
        });
    </script>
    <?php
}