Woocommerce: add free product if cart has 3 items - php

Question

What I'm trying to do is to add free product if user have 3 product in cart.
I choosed woocommerce_add_cart_item hook for this.
Here is my code :
add_filter('woocommerce_add_cart_item', 'set_item_as_free', 99, 1);
function set_item_as_free($cart_item) {
global $woocommerce;
$products_with_price = 0;
foreach ( $woocommerce->cart->get_cart() as $cart_item_key => $values ) {
if($values['data']->price == 0) {
continue;
} else {
$products_with_price++;
}
}
if( $products_with_price > 1 && $products_with_price % 3 == 1) {
$cart_item['data']->set_price(0);
return $cart_item;
}
return $cart_item;
}
I also tried $cart_item['data']->price = 0; but it doesn't work out either :(
Is there is something I do wrong or maybe there is some other way to get this done?
Thanks.

Answer 1

Try this modified code: (Have changed the condition.)
add_filter('woocommerce_add_cart_item', 'set_item_as_free', 99, 1);
function set_item_as_free($cart_item) {
global $woocommerce;
$products_with_price = 0;
foreach ( $woocommerce->cart->get_cart() as $cart_item_key => $values ) {
if($values['data']->price == 0) {
continue;
} else {
$products_with_price++;
}
}
if( $products_with_price >= 3 && $products_with_price % 3 == 1) {
$cart_item['data']->set_price(0);
return $cart_item;
}
return $cart_item;
}
If you don't want to add a free product again after a user purchases another 3 products above the existing cart then remove " && $products_with_price % 3 == 1" from the last condition.

Answer 2

Do not use the woocommerce_add_cart_item hook to set the price of the product, a lot of plugin like to refetch the price of the product in the database in the hook woocommerce_before_calculate_totals (that's the case of WPML/WCML)
So instead use this hook
add_action( 'woocommerce_before_calculate_totals', function ( $cart_obj ) {
// This is necessary for WC 3.0+
if ( is_admin() && ! defined( 'DOING_AJAX' ) ) {
return;
}
// Avoiding hook repetition (when using price calculations for example)
if ( did_action( 'woocommerce_before_calculate_totals' ) >= 2 ) {
return;
}
// Loop through cart items
foreach ( $cart_obj->get_cart() as $cart_item ) {
if ( isset( $cart_item['free_item'] ) ) {
$cart_item['data']->set_price( 0 );
}
}
} );