WooCommerce - check cart before adding item and fail validation if certain items exist

funtions.php

<?php

/**************************************************************************
 * CART VALIDATION FOR GOURMET / PACKAGES
 */

/**
 * This function loops through cart items to see if
 * there are ANY packages in it
 *
 * @return bool
 */
function does_the_cart_contain_any_packages()
{
    foreach (WC()->cart->get_cart() as $cart_item_key => $cart_item) {
        $product = $cart_item['data'];
        if (is_product_a_package($product)) {
            return true;
        }
    }

    return false;
}

/**
 * This function loops through cart items to see if
 * there are ONLY packages in it. Empty cart returns
 * false
 *
 * @return bool
 */
function does_the_cart_contain_only_packages()
{
    if (WC()->cart->get_cart_contents_count() == 0) {
        return false;
    }

    foreach (WC()->cart->get_cart() as $cart_item_key => $cart_item) {
        $product = $cart_item['data'];
        if (!is_product_a_package($product)) {
            return false;
        }
    }

    return true;
}

/**
 * This function loops through cart items to see if
 * there are ANY gourmet products in it
 *
 * @return bool
 */
function does_cart_contain_gourmet_items()
{
    foreach (WC()->cart->get_cart() as $cart_item_key => $cart_item) {
        $product = $cart_item['data'];
        if (is_product_a_gourmet_menu_item($product)) {
            return true;
        }
    }

    return false;
}

/**
 * This function checks if a given product has a package-type SKU
 *
 * @param WC_Product $product
 * @return boolean
 */
function is_product_a_package(WC_Product $product)
{
    return (strpos($product->get_sku(), "EATUP-") !== false);
}

/**
 * This function checks if a given product has a gourmet-type SKU
 *
 * @param WC_Product $product
 * @return boolean
 */
function is_product_a_gourmet_menu_item(WC_Product $product)
{
    for ($i=1; $i<7; $i++) {
        if (strpos($product->get_sku(), "m".$i."-") !== false) {
            return true;
        }
    }

    return false;
}


/**
 * This function runs as a filter when trying to add an item to the cart.
 * If gourmet items are in the cart while ordering packages or vice versa
 * the add to cart attempt will fail validation.
 *
 * @param bool $validation
 * @param int $product_id
 * @return bool
 */
function check_cart_for_packages_or_gourmet_when_adding_to_cart(bool $validation, int $product_id)
{
    if (WC()->cart->get_cart_contents_count() == 0) {
        return $validation;
    }

    $product = wc_get_product($product_id);

    if (is_product_a_package($product) && does_cart_contain_gourmet_items()) {
        wc_clear_notices();
        wc_add_notice('Please remove any gourmet meals from your <a href="/cart">shopping cart</a> before adding a package', 'error');
        $validation = false;
    }

    if (is_product_a_gourmet_menu_item($product) && does_the_cart_contain_any_packages()) {
        wc_clear_notices();
        wc_add_notice('Please remove any packages from your <a href="/cart">shopping cart</a> before adding gourmet meals', 'error');
        $validation = false;
    }

    return $validation;
}
    
add_filter('woocommerce_add_to_cart_validation', 'check_cart_for_packages_or_gourmet_when_adding_to_cart', 10, 2);