WooCommerce check cart contents on add to cart

Question

I only have one product to display, but I offer two options for it: A payment plan (handled through a subscription plugin) and a single payment. I have them displayed on my site as a grouped and both options have an "Add to Cart" Button. I don't want either option to be in the cart at the same time as the other. What I would like to do is either,

A) Empty the cart before each time the add to cart is clicked.

or

B) Check if the cart contains a product already (via productid), and remove the payment plan if the full pay is selected, or vice versa. Here is something I've come up with for this option, but I'm a bit lost and it's not functioning quite right.

        global $woocommerce;
        if ($product_id = 66){
            foreach ( $woocommerce->cart->get_cart() as $cart_item_key => $cart_item ) {
                 echo $cart_item_key;
                 if($cart_item['product_id'] == '69'){
                    //remove single product
                    $woocommerce->cart->remove_cart_item($cart_item_key);
                 }
            }
        }
        elseif ($product_id = 69){
            foreach ( $woocommerce->cart->get_cart() as $cart_item_key => $cart_item ) {
                 echo $cart_item_key;
                 if($cart_item['product_id'] == '66'){
                    //remove single product
                    $woocommerce->cart->remove_cart_item($cart_item_key);
                 }
            }
        }

I'm thinking of adding this to the add_to_cart method before the try/catch to throw any errors. Can anyone help me figure a better solution?

Answer 1

Emptying the cart would be very easy

add_filter( 'woocommerce_add_to_cart_validation', 'so_31392001_empty_cart', 10, 3 );

function so_31392001_empty_cart( $valid, $product_id, $quantity ) {

    WC()->cart->empty_cart();

    return $valid;
}