invoiceninja/app/Helpers/Invoice/Discounter.php

<?php
/**
 * Invoice Ninja (https://invoiceninja.com).
 *
 * @link https://github.com/invoiceninja/invoiceninja source repository
 *
 * @copyright Copyright (c) 2020. Invoice Ninja LLC (https://invoiceninja.com)
 *
 * @license https://opensource.org/licenses/AAL
 */

namespace App\Helpers\Invoice;

/**
 * Class for discount calculations.
 */
trait Discounter
{
    public function discount($amount)
    {
        if ($this->invoice->is_amount_discount == true) {
            return $this->invoice->discount;
        }

        return round($amount * ($this->invoice->discount / 100), 2);
    }
}