WooCommerce Dry Ice Shipping Fee Function

<?php

add_action( 'woocommerce_cart_calculate_fees', 'cwpai_shipping_class_and_item_quantity_fee', 10, 1 );
function cwpai_shipping_class_and_item_quantity_fee( $cart ) {

    ## -------------- YOUR SETTINGS BELOW ------------ ##
    $shipping_class   = 'dry-ice-shipping'; // Targeted Shipping class slug
    $initial_quantity = 3; // Quantity for the initial fee
    $step_quantity    = 3; // Quantity step for additional fees
    $initial_fee      = 30; // Fee for the initial quantity
    $additional_fee   = 30; // Additional fee per step quantity
    ## ----------------------------------------------- ##

    $total_quantity = 0; // Initializing

    // Loop through cart items
    foreach( $cart->get_cart() as $cart_item ) {
        // Get the instance of the WC_Product Object
        $product = $cart_item['data'];

        // Check for product shipping class
        if( $product->get_shipping_class() == $shipping_class ) {
            $total_quantity += $cart_item['quantity']; // Add item quantity
        }
    }

    if ( $total_quantity > 0 ) {
        $fee_text = __('Dry Ice Shipping Fee', 'codewp');
        $fee_amount = $initial_fee; // Start with the initial fee

        // Calculate additional fees based on the step quantity
        if ($total_quantity > $initial_quantity) {
            $additional_steps = ceil(($total_quantity - $initial_quantity) / $step_quantity);
            $fee_amount += $additional_steps * $additional_fee;
        }

        // Add the fee
        $cart->add_fee( $fee_text, $fee_amount );
    }
}