I am newbie to wordpress and my PHP is very limited also.

Currently I have this redirect in place –

https://stackoverflow.com/questions/48477504/woocommerce-check-and-redirect-to-login-before-checkout

However I would like to change it so that when the customer trys to access the checkout (whilst not logged in) a login modal is displayed, rather than redirecting the user anywhere. Then once the user has logged in or registered, they are able to proceed to the checkout.

I am using the “Login/Signup Popup ( Inline Form + Woocommerce )” plugin for the modal.

These are the shortcode options it gives:

As I mentioned, this is my first experience with PHP so I am still learning the basics, here is what I came up with at a completely uneducated guess, using the redirect script as a template –

add_action('display_login_modal','check_if_logged_in');
function check_if_logged_in()
{
    $pageid = 257; // Checkout page ID
    if(!is_user_logged_in() && is_page($pageid))
    {
        $shortcode = add_query_arg(
            'display_modal',
            get_permalink($pageid),
            short_code('xoo-el-login-tgr') //Popup shortcode
        );
        wp_display_modal($shortcode);
        exit;
    }
}

I know it’s way off so any help or tips would be greatly appreciated!

Cheers