Update project structure and build process

libwallet/operation/fees.go

@@ -0,0 +1,60 @@
+package operation
+
+import (
+	"math"
+)
+
+type feeCalculator struct {
+	NextTransactionSize *NextTransactionSize
+}
+
+// Fee DOES NOT return error when amount > balance. Instead we return the fee it would take to
+// spend all utxos and delegate to the caller the task of checking if that is spendable with the given
+// amount. This is to avoid using go error handling.
+// Consequences of this:
+// - we don't check balance whatsoever
+// - fee for COLLECT swap is exactly the same as normal case
+func (f *feeCalculator) Fee(amountInSat int64, feeRateInSatsPerVByte float64, takeFeeFromAmount bool) int64 {
+	if amountInSat == 0 {
+		return 0
+	}
+	if takeFeeFromAmount {
+		return f.feeFromAmount(amountInSat, feeRateInSatsPerVByte)
+	} else {
+		return f.feeFromRemainingBalance(amountInSat, feeRateInSatsPerVByte)
+	}
+}
+
+func (f *feeCalculator) feeFromAmount(amountInSat int64, feeRateInSatsPerVByte float64) int64 {
+	if f.NextTransactionSize == nil {
+		return 0
+	}
+
+	var fee int64
+	for _, sizeForAmount := range f.NextTransactionSize.SizeProgression {
+		fee = computeFee(sizeForAmount.SizeInVByte, feeRateInSatsPerVByte)
+		if sizeForAmount.AmountInSat >= amountInSat {
+			break // no more UTXOs needed
+		}
+	}
+	return fee
+}
+
+func (f *feeCalculator) feeFromRemainingBalance(amountInSat int64, feeRateInSatsPerVByte float64) int64 {
+	if f.NextTransactionSize == nil {
+		return 0
+	}
+
+	var fee int64
+	for _, sizeForAmount := range f.NextTransactionSize.SizeProgression {
+		fee = computeFee(sizeForAmount.SizeInVByte, feeRateInSatsPerVByte)
+		if sizeForAmount.AmountInSat >= amountInSat+fee {
+			break // no more UTXOs needed
+		}
+	}
+	return fee
+}
+
+func computeFee(sizeInVByte int64, feeRate float64) int64 {
+	return int64(math.Ceil(float64(sizeInVByte) * feeRate))
+}