WooCommerce: Get discount total only for items from a specific tax class

I want to export only the coupon totals from items with reduced tax rate (the totals you can see in the image below).

With the totals of these items I do the same. A great answer helped me to export only the totals of order items with reduced tax rate. For that I'm using the following code:

// gets the total of the order items by tax class
function get_total_order_items_by_tax_class( $order_id, $tax_class = 'reduced-rate' ) {
    $order = wc_get_order( $order_id );
    // initializes the total of the order items
    $total = 0;
    foreach( $order->get_items() as $item_id => $order_item ) {
        // if the product tax class is equal to "$tax_class"
        if ( $tax_class == $order_item['tax_class'] ) {
            // sum the total
            $total += $order_item['total'];
        }
    }
    return $total;
}

I tried something similar and added the line (found here):

$order->get_discount_total();

to the snippet. But this exports the whole discount for every item of every tax class.

I also tried the following code from this answer:

foreach( $order->get_coupon_codes() as $coupon_code ) {
    // Get the WC_Coupon object
    $coupon = new WC_Coupon($coupon_code);

    $discount_type = $coupon->get_discount_type(); // Get coupon discount type
    $coupon_amount = $coupon->get_amount(); // Get coupon amount
}

But it's also the discount for the whole order.

Is there any way to get the discount totals only for items with reduced tax rates? I believe that there must be a way because the order shows these totals below every item. But I couldn't find a way to get these discounts.

I saw that $order only contains the coupon total and the coupon tax. Not per line item. And it seems that $order_item doesn't contain any discounts. Only something line WC_Coupon_Data_Store_CPT.

Solution

Try the following to get order items discount amount by tax class:

// Get order items discount amount excl. taxes by tax class
function get_order_items_discount_total_by_tax_class( $order_id, $tax_class = 'reduced-rate' ) {
    $order    = wc_get_order( $order_id );
    $discount = 0; // Initializing;

    foreach( $order->get_items() as $item ) {
        // if the product tax class is equal to "$tax_class"
        if ( $tax_class == $item['tax_class'] ) {
            $discount += $item->get_subtotal() - $item->get_total(); // Excluding taxes
        }
    }
    return $discount;
}

It should work.