Add only one product to cart

For selling just one item, for example when you have to pick from multiple prices in a pricing table. This snippet will remove the other products from the cart, and add the current product and will redirect you to checkout. It will also remove the order again button.

<?php
add_filter( 'woocommerce_add_to_cart_redirect', function() {
   return wc_get_checkout_url();
});

add_filter( 'wc_add_to_cart_message_html' , function() {
   return '';
});
 

add_filter( 'woocommerce_add_to_cart_validation', function( $passed, $product_id, $quantity ) {
    if( ! WC()->cart->is_empty() ) {
        WC()->cart->empty_cart();
    }

    return $passed;
}
, 20, 3 );

remove_action( 'woocommerce_order_details_after_order_table', 'woocommerce_order_again_button' );