Prevent mixture of a specific category and other products in same cart

Prevent mixture of a specific category and other products in same cart.php

/*
 * Prevent mixture of a specific category and other products in same cart
 */
function ns_dont_add_booklet_to_cart_containing_other($validation, $product_id) {

		// Set flag false until we find a product in cat booklet
    $cart_has_booklets = false;

		// Set $cat_check true if a cart item is in booklet cat
    foreach (WC()->cart->get_cart() as $cart_item_key => $cart_item) {

        $product = $cart_item['data'];

        if (has_term('booklet', 'product_cat', $product->id)) {
            $cart_has_booklets = true;
            // break because we only need one "true" to matter here
            break;
        }
    }

    $product_is_booklets = false;
    if (has_term('booklet', 'product_cat', $product_id)) {
        $product_is_booklets = true;
    }

		// Return true if cart empty
    if (!WC()->cart->get_cart_contents_count() == 0) {
        // If cart contains booklet and product to be added is not booklet, display error message and return false.
        if ($cart_has_booklets && !$product_is_booklets) {
            wc_add_notice('Due to technical difficulties we are currently unable to process free, paid for or marketing products in the same order. Please note this is only temporary while we work hard to find a long term solution. We are sorry for any inconvenience this may cause.  If you experience any difficulties please raise a ticket through our <a href="https://helpdesk.autismeducationtrust.org.uk/"> helpdesk</a>', 'error');
            $validation = false;
        }


        // If cart contains a product that is not booklet and product to be added is booklet, display error message and return false.
        elseif (!$cart_has_booklets && $product_is_booklets) {
            wc_add_notice('Due to technical difficulties we are currently unable to process free, paid for or marketing products in the same order.Please note this is only temporary while we work hard to find a long term solution. We are sorry for any inconvenience this may cause.  If you experience any difficulties please raise a ticket through our <a href="https://helpdesk.autismeducationtrust.org.uk/"> helpdesk</a>', 'error');
            $validation = false;
        }
    }
    // Otherwise, return true.
    return $validation;
}

add_filter('woocommerce_add_to_cart_validation', 'ns_dont_add_booklet_to_cart_containing_other', 10, 2);