public function determineFeeAndChange(TransactionBuilder $txBuilder)
{
$send = $txBuilder->getOutputs();
$utxos = $txBuilder->getUtxos();
$fee = $txBuilder->getFee();
$change = null;
// if the fee is fixed we just need to calculate the change
if ($fee !== null) {
$change = $this->determineChange($utxos, $send, $fee);
// if change is not dust we need to add a change output
if ($change > Blocktrail::DUST) {
$send[] = ['address' => 'change', 'value' => $change];
} else {
// if change is dust we do nothing (implicitly it's added to the fee)
$change = 0;
}
} else {
$fee = $this->determineFee($utxos, $send);
$change = $this->determineChange($utxos, $send, $fee);
if ($change > 0) {
$changeIdx = count($send);
// set dummy change output
$send[$changeIdx] = ['address' => 'change', 'value' => $change];
// recaculate fee now that we know that we have a change output
$fee2 = $this->determineFee($utxos, $send);
// unset dummy change output
unset($send[$changeIdx]);
// if adding the change output made the fee bump up and the change is smaller than the fee
// then we're not doing change
if ($fee2 > $fee && $fee2 > $change) {
$change = 0;
} else {
$change = $this->determineChange($utxos, $send, $fee2);
// if change is not dust we need to add a change output
if ($change > Blocktrail::DUST) {
$send[$changeIdx] = ['address' => 'change', 'value' => $change];
} else {
// if change is dust we do nothing (implicitly it's added to the fee)
$change = 0;
}
}
}
}
$fee = $this->determineFee($utxos, $send);
return [$fee, $change];
}
