Add custom checkout field based on product category in Woocommerce

I need to add custom checkout field based on product category. I found this code which works with products, but it is very time consuming to add Ids from every new product from particular category.

function is_in_cart() {
    // Add your special product IDs here
    $ids = array( 12468, 9687, 9693);

    foreach( WC()->cart->get_cart() as $cart_item ){
        $product_id = version_compare( WC_VERSION, '3.0', '<' ) ? $cart_item['data']->id : $cart_item['data']->get_id();
        if( in_array( $cart_item['data']->get_id(), $ids ) )
            return true;
    }
    return false;
}

 /**
 * Add the field to the checkout
 */
add_action( 'woocommerce_before_order_notes', 'custom_checkout_field', 20 );

function custom_checkout_field( $checkout ) {
if( ! is_in_cart() ){
    woocommerce_form_field( 'special_field', array(
        'type'          => 'textarea',
        'class'         => array('form-row-wide'),
        'label'         => pll__('Special text'),
        'required'      => false,
        'label_class'   => array('specialfieldclass'),
        'clear'         => false,
        ), $checkout->get_value( 'special_field' ));
}
}

How to modify this code to work with product categories?

Answer

Try the following to handle product categories (handling parent terms too):

// Custom conditional function that handle parent product categories too
function has_product_categories( $categories, $product_id = 0 ) {
    $parent_term_ids = $categories_ids = array(); // Initializing
    $taxonomy        = 'product_cat';
    $product_id      = $product_id == 0 ? get_the_id() : $product_id;

    if( is_string( $categories ) ) {
        $categories = (array) $categories; // Convert string to array
    }

    // Convert categories term names and slugs to categories term ids
    foreach ( $categories as $category ){
        $result = (array) term_exists( $category, $taxonomy );
        if ( ! empty( $result ) ) {
            $categories_ids[] = reset($result);
        }
    }

    // Loop through the current product category terms to get only parent main category term
    foreach( get_the_terms( $product_id, $taxonomy ) as $term ){
        if( $term->parent > 0 ){
            $parent_term_ids[] = $term->parent; // Set the parent product category
            $parent_term_ids[] = $term->term_id; // (and the child)
        } else {
            $parent_term_ids[] = $term->term_id; // It is the Main category term and we set it.
        }
    }
    return array_intersect( $categories_ids, array_unique($parent_term_ids) ) ? true : false;
}

// Custom conditional function that check for product categories
function is_in_cart() {
    // HERE your product categories
    $categories = array( 'clothing' );

    foreach( WC()->cart->get_cart() as $cart_item ){
        if( has_product_categories( $cart_item['product_id'], $categories ) )
            return true;
    }
    return false;
}

 // Add a checkout field before order notes
add_action( 'woocommerce_before_order_notes', 'custom_checkout_field', 20 );
function custom_checkout_field( $checkout ) {
    if( ! is_in_cart() ){
        woocommerce_form_field( 'special_field', array(
            'type'          => 'textarea',
            'class'         => array('form-row-wide'),
            'label'         => pll__('Special text'),
            'required'      => false,
            'label_class'   => array('specialfieldclass'),
            'clear'         => false,
            ), $checkout->get_value( 'special_field' ));
    }
}

Code goes in functions.php file of your active child theme (or active theme). It should works.