Set Woocommerce products category items prices when a specific product ID is in cart

Question

I am trying to achieve the following:

• A customer adds Product 1 (from category Books) to cart which costs $10.
• Then he adds to cart Product 2.

How to make if Product 2 is in cart, make Product 1 = $0 and all added products from category Books $0?

My idea is if a customer buys a certain product this makes free all products of a product category.

So far I got this, but is it is not working and is making all of the products in cart to $0:

add_action( 'woocommerce_before_calculate_totals', 'change_price_if_6245_in_cart' );
function change_price_if_6245_in_cart( $cart_object ) {
        if (woo_in_cartbooks (6245) ) {
    // set our flag to be false until we find a product in that category
    $cat_check = false;

    // check each cart item for our category
    foreach ( WC()->cart->get_cart() as $cart_item_key => $cart_item ) {

        $product = $cart_item['data'];

        // replace 'books' with your category's slug
        if ( has_term( 'books', 'product_cat', $product->id ) ) {
            $cat_check = true;
            // break because we only need one "true" to matter here
            break;
        }
    }

    // if a product in the cart is in our category, do something
    if ( $cat_check  ) {
        // we have the category, do what we want
        foreach ( $cart_object->get_cart() as $hash => $value ) {
            $value['data']->set_price( 0 );
        }
    }
}

Answer 1

Here is the correct way to make it work (code is commented):

add_action( 'woocommerce_before_calculate_totals', 'free_product_category_for_a_specific_product', 20, 1 );
function free_product_category_for_a_specific_product( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    if ( did_action( 'woocommerce_before_calculate_totals' ) >= 2 )
        return;

    // HERE Below your settings
    $product_category = "books"; // <= The product category (can be an ID, a slug or a name)
    $specific_product_id = 6245; // <= The specific product ID

    $found = false;

    // 1st cart items Loop: Check for specific product
    foreach ( $cart->get_cart() as $cart_item ) {
        // Check for 'books' with your category's slug
        if ( $cart_item['data']->get_id() == $specific_product_id ) {
            $found = true;
            break; // Found, we stop first loop
        }
    }
    // If specific product is not in cart we exit
    if( ! $found ) 
        return;

    // 2nd cart items Loop: check items remaining to "Books" product category when specific product is in cart
    foreach ( $cart->get_cart() as $cart_item ) {
        // If specific product has been found, we set price to 0 for items remaining to "Books" product category
        if ( has_term( $product_category, 'product_cat', $cart_item['product_id'] ) ) {
            $cart_item['data']->set_price( 0 );
        }
    }
}

Code goes in function.php file of your active child theme (or active theme). Tested and works.