public function refundAmount(Money $threshold)
{
// todo include forgiven?
$unpaidAmount = $this->unpaidAmount();
$thresholdAmount = $unpaidAmount->add($threshold);
if ($this->repaymentAmount->greaterThan($thresholdAmount)) {
return $this->repaymentAmount->subtract($unpaidAmount->ceil());
}
return Money::create(0);
}