Changing WooCommerce coupon discount amount in cart - php

Question

What I'm doing:
I am creating a coupon based promo. The coupon will discount 10% of the most expensive item in the cart that belongs to a specific product category.
The problem:
The code below successfully checks if the cart contains products from the specific category, and obtains 10% of the price of the most expensive product from that array to use for the discount. However, I can't get the coupon discount amount to change in the cart.
The code:
function change_coupon_price_for_promo( $cart ) {
if ( is_admin() && ! defined( 'DOING_AJAX' ) ){
return;
}
// coupon code
$coupon_name = 'MYCOUPONNAME';
// if coupon is applied to cart...
if( $cart->has_discount( $coupon_name ) ) {
// Form array of products from the cart that belong to the specified category
$specProduct = array(); // array of specific products in cart
foreach ( $cart->get_cart() as $key => $cart_item ) {
$cart_item_id = $cart_item['product_id'];
$terms = wp_get_post_terms( $cart_item_id, 'product_cat' );
foreach ( $terms as $term ){
// gets product cat id
$product_cat_id = $term->term_id;
// gets an array of all parent category levels
$product_parent_categories_all_hierachy = get_ancestors( $product_cat_id, 'product_cat' );
// This cuts the array and extracts the last set in the array
$last_parent_cat = array_slice($product_parent_categories_all_hierachy, -1, 1, true);
if(in_array(3831, $last_parent_cat)){
$specProduct[$key] = $cart_item_id;
break;
}
}
}
//if there are items from the specific category in the cart
if(!empty($specProduct)){
$specPriceArray = array(); // array of specific product prices in cart
foreach ($specProduct as $key => $specItem) {
$thisProd = wc_get_product($specItem);
$thisPrice = $thisProd->get_price();
$specPriceArray[$key] = $thisPrice;
}
// most expensive specific product price
$highestSpec = max($specPriceArray);
// discount of most expensive item
$finalDiscount = $highestSpec * .1;
// print_r($specProduct); GOOD
// print_r($specPriceArray); GOOD
// echo $highestSpec; GOOD
// echo $finalDiscount; GOOD
/***** APPLY COUPON CHANGE HERE<-------HOW??? *****/
$cart->discount_total = $finalDiscount;
}
}
}
add_action( 'woocommerce_before_calculate_totals', 'change_coupon_price_for_promo', 10, 1 );
What I'm asking:
The last line of the code before the closing brackets...
$cart->discount_total = $finalDiscount;
is what I tried using to change the coupon's discount in the cart. It doesn't work. How can I accomplish this? TY.
EDIT:
I should note that the coupon being added is set up as a "Fixed cart discount" with a rate of 0 so it is added as a line item to the order. This way the user sees the discount for the coupon code on its own line in the cart/checkout.

Answer 1

you can use function set_price.
you can call it in your code like:
$cart_item['data']->set_price('New price here')
use this inside the foreach that loops your cart items