newsupernova/vendor/magento/module-sales/Model/Order/Invoice/Total/Subtotal.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Sales\Model\Order\Invoice\Total;

class Subtotal extends AbstractTotal
{
    /**
     * Collect invoice subtotal
     *
     * @param \Magento\Sales\Model\Order\Invoice $invoice
     * @return $this
     */
    public function collect(\Magento\Sales\Model\Order\Invoice $invoice)
    {
        $subtotal = 0;
        $baseSubtotal = 0;
        $subtotalInclTax = 0;
        $baseSubtotalInclTax = 0;

        $order = $invoice->getOrder();

        foreach ($invoice->getAllItems() as $item) {
            if ($item->getOrderItem()->isDummy()) {
                continue;
            }

            $item->calcRowTotal();

            $subtotal += $item->getRowTotal();
            $baseSubtotal += $item->getBaseRowTotal();
            $subtotalInclTax += $item->getRowTotalInclTax();
            $baseSubtotalInclTax += $item->getBaseRowTotalInclTax();
        }

        $allowedSubtotal = $order->getSubtotal() - $order->getSubtotalInvoiced();
        $baseAllowedSubtotal = $order->getBaseSubtotal() - $order->getBaseSubtotalInvoiced();
        //Note: The $subtotalInclTax and $baseSubtotalInclTax are not adjusted from those provide by the line items
        //because the "InclTax" is displayed before any tax adjustments based on discounts, shipping, etc.

        if ($invoice->isLast()) {
            $subtotal = $allowedSubtotal;
            $baseSubtotal = $baseAllowedSubtotal;
        } else {
            $subtotal = min($allowedSubtotal, $subtotal);
            $baseSubtotal = min($baseAllowedSubtotal, $baseSubtotal);
        }

        $invoice->setSubtotal($subtotal);
        $invoice->setBaseSubtotal($baseSubtotal);
        $invoice->setSubtotalInclTax($subtotalInclTax);
        $invoice->setBaseSubtotalInclTax($baseSubtotalInclTax);

        $invoice->setGrandTotal($invoice->getGrandTotal() + $subtotal);
        $invoice->setBaseGrandTotal($invoice->getBaseGrandTotal() + $baseSubtotal);
        return $this;
    }
}