Auto add or remove a freebie product from cart in Woocommerce

Question

I'm operating a WooCommerce shop, where we'd like to give every customer a freebie (e-book) that will show in the basket, after you have added a product to the basket obvious.

Example:
You add "product1" to the basket, and the basket will now show 2 products. the "product1" and the "freebie". When you remove the product from the basket, the freebie will be removed again.

I got this code for now:

add_action( 'woocommerce_add_to_cart', 'check_freebie_exists', 10, 6 );
function check_freebie_exists($cart_item_key, $product_id, $quantity, $variation_id, $variation, $cart_item_data) {
    if($product_id == 1234) { // obviously replace this with the product that triggers the freebie
        /* or you could use
        if(has_term($cat_id, 'product_cat', $product_id)) { to check if a product is in a particular product_cat
        or you could check anything else related to the product
        */
        $hasfreebie = false;
        // loop through the cart to check the freebie is not already there
        global $woocommerce;
        $cart = $woocommerce->cart->get_cart();
        foreach($cart as $key => $values) {
            if($values['data']->id == $your_freebie_product_id) {
                $hasfreebie = true;
                break;
            }
        }
        if(!$hasfreebie) {
            $woocommerce->cart->add_to_cart($your_freebie_product_id);
        }
    }
}

add_action( 'woocommerce_cart_item_removed', 'remove_freebie', 10, 2 );
function remove_freebie( $cart_item_key, $cart ) {
    $hasmaster = false;
    $freebiekey = NULL;
    foreach($cart as $key => $values) {
        if($values['data']->id == 1234) { // check that we have the product that should trigger the freebie
            $hasmaster = true;
        } elseif($values['data']->id == $your_freebie_product_id) {
            $freebiekey = $key;
        }
    }
    if(!$hasmaster && $freebiekey) {
        $cart->remove_cart_item($freebiekey);
    }
}

But it doesn't seem to be working quite yet.

What I am doing wrong?

Any help will be really appreciated.

Answer 1

Update 2 - October 2018 - Improved and enhanced code (Completely revisited)

The following code will add a freebie product on first add to cart just once. If all other cart items are removed, the freebie item will be removed too:

add_action( 'woocommerce_before_calculate_totals', 'add_remove_freebie', 50, 1 );
function add_remove_freebie( $cart ) {

    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

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

    $freebie_id = 70; // <== HERE set the freebie product ID
    $has_others = false;

    // Loop through cart items
    foreach( $cart->get_cart() as $cart_item_key => $cart_item ) {
        // Added Woocommerce compatibility version
        $product_id = version_compare( WC_VERSION, '3.0', '<' ) ? $cart_item['data']->id : $cart_item['data']->get_id();

        if( $product_id == $freebie_id ) {
            // Freebie is in cart
            $freebie_key = $cart_item_key;
        } else {
            // Other items are in cart
            $has_others = true;
        }
    }
    // If freebie product is alone in cart we remove it
    if( ! $has_others && isset( $freebie_key ) ){
        $cart->remove_cart_item( $freebie_key );
    } elseif ( $has_others && ! isset( $freebie_key ) ) {
        $cart->add_to_cart($freebie_id);
    }
}

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