I am trying to apply a percentage discount based on quantity of products with a specific product attribute, in cart.

More precisely my goal is to apply 15% discount on orders of minimum 6 products with the attribute flaske.

I have managed to achieve this for variable products with variation attributes set, but I can’t seem to target the single/simple products.

My code so far (borrowed from Condition for Quantity and Price for Woocommerce):

// Discount based on product quantity and attribute in cart
add_action( 'woocommerce_cart_calculate_fees','wc_cart_item_quantity_discount' );
function wc_cart_item_quantity_discount( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    // INITIALIZING VARIABLES
    $min_item_amount = 6; // Min quantity
    $discount = $items_count = $percent = $items_subtotal = 0;
    $taxonomy   = 'pa_variant'; // Taxonomy
    $term_slugs = array('flaske'); // Term/terms
    // Loop through cart items
    foreach( $cart->get_cart() as $cart_item_key => $cart_item ) {
      // Loop through variation
      foreach( $cart_item['variation'] as $attribute => $term_slug ) {
        // Only counting items that are above 6 and has attribute
        if( $cart_item['data']->get_price() >= $min_item_amount && $attribute === 'attribute_'.$taxonomy && in_array( $term_slug, $term_slugs ) ) {
            $items_count += $cart_item['quantity'];
            $items_subtotal += $cart_item['line_subtotal'];
        }
      }
    }
    // CONDITIONAL PERCENTAGE
    if ($items_count >= 6 ) {
        $percent = 15;
    }
    // DISCOUNT (TAXABLE)
    if( $items_count > 0 ) {
        // Calculation
        $discount -= ($items_subtotal / 100) * $percent;
        $cart->add_fee( __( "Mix & Match rabat - $percent%", "woocommerce" ), $discount, true);
    }
}

My current code works very well for variable products (the variants), but it doesn’t seem to affect single products, even if I give the single products the same attributes as the variable product.

I suspect it has to do with the foreach loop foreach( $cart_item['variation'] as $attribute => $term_slug )

How can I make this work in general, so it also applies for single/simple products with same attribute flaske?

Any help and advice would be appreciated.

Other useful references:

Woocommerce percentage discount per item based on quantity

Exclude variations with 2 specific attribute terms from coupon usage in Woocommerce