Woocommerce: add to cart automatically when visiting a page (variable product IDs)

Question

I am aware that there's already an existing function where you can add a certain product on cart upon visiting the website. The problem is you can only do it with 1 product and I want it variable depending on the page you are visiting.

here's the existing code (added on functions.php file)

add_action( 'template_redirect', 'add_product_to_cart' );
function add_product_to_cart() {
    if ( ! is_admin() ) {
        $product_id = 275;
        $found = false;
        //check if product already in cart
        if ( sizeof( WC()->cart->get_cart() ) > 0 ) {
            foreach ( WC()->cart->get_cart() as $cart_item_key => $values ) {
                $_product = $values['data'];
                if ( $_product->id == $product_id )
                    $found = true;
            }
            // if product not found, add it
            if ( ! $found )
                WC()->cart->add_to_cart( $product_id );
        } else {
            // if no products in cart, add it
            WC()->cart->add_to_cart( $product_id );
        }
    }
}

Inside my landing page called page-template.php, there's a custom field that echos the ID of a certain product selected. So when my user visits this page, I want this ID to replace the $product_id on the functions.php file. How do I achieve this?

Many thanks in advance for the help.

Answer 1

maybe the global variable is loaded after the function. instead of just setting the variable initiate the function passing the variable and avoid the hook:

in functions.php:

function add_product_to_cart($product_id) {
    if ( ! is_admin() ) {
        $found = false;
        //check if product already in cart
        if ( sizeof( WC()->cart->get_cart() ) > 0 ) {
            foreach ( WC()->cart->get_cart() as $cart_item_key => $values ) {
                $_product = $values['data'];
                if ( $_product->id == $product_id )
                    $found = true;
            }
            // if product not found, add it
            if ( ! $found )
                WC()->cart->add_to_cart( $product_id );
        } else {
            // if no products in cart, add it
            WC()->cart->add_to_cart( $product_id );
        }
    }
}

in page-template.php:

add_product_to_cart(275);