conditionally show a custom product badge

gistfile1.txt

/**
 * @snippet       Checkbox to display Custom Product Badge Part 1 - WooCommerce
 * @author        Fabio Tielen // Code Agency // https://codeagency.be
 * @testedwith    Woo 3.3+
 */
  
// -----------------------------------------
// STEP 1. adding a custom checkbox to product edit page
  
add_action( 'woocommerce_product_options_general_product_data', 'codeagency_add_badge_checkbox_to_products' );        
  
function codeagency_add_badge_checkbox_to_products() {           
woocommerce_wp_checkbox( array( 
'id' => 'custom_badge', 
'class' => '', 
'label' => 'Custom Badge Visible'
) 
);      
}
  
// -----------------------------------------
// STEP 2. Save checkbox value via custom field
  
add_action( 'save_post', 'codeagency_save_badge_checkbox_to_post_meta' );
  
function codeagency_save_badge_checkbox_to_post_meta( $product_id ) {
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
        return;
    if ( isset( $_POST['custom_badge'] ) ) {
            update_post_meta( $product_id, 'custom_badge', $_POST['custom_badge'] );
    } else delete_post_meta( $product_id, 'custom_badge' );
}

// -----------------------------------------
// STEP 3. Show the custom badge on single product page
  
add_action( 'woocommerce_single_product_summary', 'codeagency_display_badge', 6 );
  
function codeagency_display_badge() {
    global $product;     
    if ( get_post_meta( $product->get_id(), 'custom_badge', true ) ) {
        echo '<div class="woocommerce-message">FREE SHIPPING!</div>';
    }
}