Restrict Woocommerce to only allowing purchases from a sinlge parent category

I have this the following but doesn’t seem to work quite right

function is_product_the_same_cat($valid, $product_id, $quantity) {
global $woocommerce;
// start of the loop that fetches the cart items
foreach ( $woocommerce->cart->get_cart() as $cart_item_key => $values ) {
$_product = $values[‘data’];
$terms = get_the_terms( $_product->id, ‘product_cat’ );
$target_terms = get_the_terms( $product_id, ‘product_cat’ ); //get the current items
foreach ($terms as $term) {
$cat_ids[] = $term->term_id; //get all the item categories in the cart
}
foreach ($target_terms as $term) {
$target_cat_ids[] = $term->term_id; //get all the categories of the product
}
}
$same_cat = array_intersect($cat_ids, $target_cat_ids); //check if they have the same category
if(count($same_cat) > 0) return $valid;
else {
wc_add_notice( ‘This product is in another category!’, ‘error’ );
return false;
}
}
add_filter( ‘woocommerce_add_to_cart_validation’, ‘is_product_the_same_cat’,10,3);

############## and also ###################

// Enforce single parent category items in cart at a time based on first item in cart
function get_product_top_level_category ( $product_id ) {

$product_terms = get_the_terms ( $product_id, ‘product_cat’ );
$product_category = $product_terms[0]->parent;
$product_category_term = get_term ( $product_category, ‘product_cat’ );
$product_category_parent = $product_category_term->parent;
$product_top_category = $product_category_term->term_id;

while ( $product_category_parent != 0 ) {
$product_category_term = get_term ( $product_category_parent, ‘product_cat’ );
$product_category_parent = $product_category_term->parent;
$product_top_category = $product_category_term->term_id;
}

return $product_top_category;
}

add_filter ( ‘woocommerce_before_cart’, ‘restrict_cart_to_single_category’ );
function restrict_cart_to_single_category() {
global $woocommerce;
$cart_contents = $woocommerce->cart->get_cart( );
$cart_item_keys = array_keys ( $cart_contents );
$cart_item_count = count ( $cart_item_keys );

// Do nothing if the cart is empty
// Do nothing if the cart only has one item
if ( ! $cart_contents || $cart_item_count == 1 ) {
return null;
}

// Multiple Items in cart
$first_item = $cart_item_keys[0];
$first_item_id = $cart_contents[$first_item][‘product_id’];
$first_item_top_category = get_product_top_level_category ( $first_item_id );
$first_item_top_category_term = get_term ( $first_item_top_category, ‘product_cat’ );
$first_item_top_category_name = $first_item_top_category_term->name;

// Now we check each subsequent items top-level parent category
foreach ( $cart_item_keys as $key ) {
if ( $key == $first_item ) {
continue;
}
else {
$product_id = $cart_contents[$key][‘product_id’];
$product_top_category = get_product_top_level_category( $product_id );

if ( $product_top_category != $first_item_top_category ) {
$woocommerce->cart->set_quantity ( $key, 0, true );
$mismatched_categories = 1;
}
}
}

// we really only want to display this message once for anyone, including those that have carts already prefilled
if ( isset ( $mismatched_categories ) ) {
echo ‘<p class=”woocommerce-error”>Only one category allowed in cart at a time.<br />You are currently allowed only ‘.$first_item_top_category_name.’ items in your cart.<br />To order a different category empty your cart first.</p>’;
}
}

This method works, tested and tried. Add to your functions.php. file at the end.

 // Enforce single parent category items in cart at a time based on first item in cart
    function get_product_top_level_category ( $product_id ) {
    
            $product_terms            =  get_the_terms ( $product_id, 'product_cat' );
            $product_category         =  $product_terms[0]->parent;
            $product_category_term    =  get_term ( $product_category, 'product_cat' );
            $product_category_parent  =  $product_category_term->parent;
            $product_top_category     =  $product_category_term->term_id;
    
            while ( $product_category_parent  !=  0 ) {
                    $product_category_term    =  get_term ( $product_category_parent, 'product_cat' );
                    $product_category_parent  =  $product_category_term->parent;
                    $product_top_category     =  $product_category_term->term_id;
            }
    
            return $product_top_category;
    }
    
    add_filter ( 'woocommerce_before_cart', 'restrict_cart_to_single_category' );
    function restrict_cart_to_single_category() {
            global $woocommerce;
            $cart_contents    =  $woocommerce->cart->get_cart( );
            $cart_item_keys   =  array_keys ( $cart_contents );
            $cart_item_count  =  count ( $cart_item_keys );
    
            // Do nothing if the cart is empty
            // Do nothing if the cart only has one item
            if ( ! $cart_contents || $cart_item_count == 1 ) {
                    return null;
            }
    
            // Multiple Items in cart
            $first_item                    =  $cart_item_keys[0];
            $first_item_id                 =  $cart_contents[$first_item]['product_id'];
            $first_item_top_category       =  get_product_top_level_category ( $first_item_id );
            $first_item_top_category_term  =  get_term ( $first_item_top_category, 'product_cat' );
            $first_item_top_category_name  =  $first_item_top_category_term->name;
    
            // Now we check each subsequent items top-level parent category
            foreach ( $cart_item_keys as $key ) {
                    if ( $key  ==  $first_item ) {
                            continue;
                    }
                    else {
                            $product_id            =  $cart_contents[$key]['product_id'];
                            $product_top_category  =  get_product_top_level_category( $product_id );
    
                            if ( $product_top_category  !=  $first_item_top_category ) {
                                    $woocommerce->cart->set_quantity ( $key, 0, true );
                                    $mismatched_categories  =  1;
                            }
                    }
            }
    
            // we really only want to display this message once for anyone, including those that have carts already prefilled
            if ( isset ( $mismatched_categories ) ) {
                    echo '<p class="woocommerce-error">Only one category allowed in cart at a time.<br />You are currently allowed only <strong>'.$first_item_top_category_name.'</strong> items in your cart.<br />To order a different category empty your cart first.</p>';
            }
    }

Awesome @mikon82, this works really well and just what I was looking for.
All the best