make shipping free when specific optional fee is selected

gistfile1.txt

class PISOL_Zero_Shipping_On_Fee {

	static $instance = null;
	
	public static function get_instance() {
		if ( null === self::$instance ) {
			self::$instance = new self();
		}
		return self::$instance;
	}

	protected function __construct() {
		add_action('wp_loaded', array($this, 'clear_wc_shipping_rates_cache'));
		add_filter( 'woocommerce_package_rates', array( $this, 'maybe_zero_shipping_rates' ), PHP_INT_MAX, 2 );
	}

	function clear_wc_shipping_rates_cache(){
        if(!isset(WC()->cart) || !function_exists('WC')) return;
        
        if ( !WC()->customer ) return; // this allows it to work with woocommerce point of sales plugin
        
        $packages = WC()->cart->get_shipping_packages();

        foreach ($packages as $key => $value) {
            $shipping_session = "shipping_for_package_$key";

            unset(WC()->session->$shipping_session);
        }
        
   }
	
	public function maybe_zero_shipping_rates( $rates, $package ) {

		if(!class_exists('Pi_cefw_Apply_fees')){
			return $rates;
		}

		if ( ! Pi_cefw_Apply_fees::feesChecked( 1137 ) ) {
			return $rates;
		}

		foreach ( $rates as $rate_id => $rate ) {
			if ( ! empty( $this->allowed_shipping_method_ids ) && ! in_array( $rate_id, $this->allowed_shipping_method_ids, true ) ) {
				continue;
			}

			if ( is_object( $rate ) ) {
				if ( method_exists( $rate, 'set_cost' ) ) {
					$rate->set_cost( 0 );
				} else {
					$rate->cost = 0;
				}

				if ( property_exists( $rate, 'taxes' ) ) {
					$rate->taxes = array();
				}

				$label = $rate->get_label ? $rate->get_label() : ( isset( $rate->label ) ? $rate->label : '' );
				if ( ! empty( $label ) ) {
					$new_label = $label . ' (shipping waived)';
					if ( method_exists( $rate, 'set_label' ) ) {
						$rate->set_label( $new_label );
					} else {
						$rate->label = $new_label;
					}
				}

			} else {
				if ( is_array( $rate ) ) {
					$rates[ $rate_id ]['cost'] = 0;
					$rates[ $rate_id ]['taxes'] = array();
					if ( isset( $rates[ $rate_id ]['label'] ) ) {
						$rates[ $rate_id ]['label'] .= ' (shipping waived)';
					}
				}
			}
		}

		return $rates;
	}
}
PISOL_Zero_Shipping_On_Fee::get_instance();