package models

import "github.com/lightningnetwork/lnd/lnwire"

const (
	// maxFeeRate is the maximum fee rate that we allow. It is set to allow
	// a variable fee component of up to 10x the payment amount.
	maxFeeRate = 10 * feeRateParts
)

type InboundFee struct {
	Base int32
	Rate int32
}

// NewInboundFeeFromWire constructs an inbound fee structure from a wire fee.
func NewInboundFeeFromWire(fee lnwire.Fee) InboundFee {
	return InboundFee{
		Base: fee.BaseFee,
		Rate: fee.FeeRate,
	}
}

// ToWire converts the inbound fee to a wire fee structure.
func (i *InboundFee) ToWire() lnwire.Fee {
	return lnwire.Fee{
		BaseFee: i.Base,
		FeeRate: i.Rate,
	}
}

// CalcFee calculates what the inbound fee should minimally be for forwarding
// the given amount. This amount is the total of the outgoing amount plus the
// outbound fee, which is what the inbound fee is based on.
func (i *InboundFee) CalcFee(amt lnwire.MilliSatoshi) int64 {
	fee := int64(i.Base)
	rate := int64(i.Rate)

	// Cap the rate to prevent overflows.
	switch {
	case rate > maxFeeRate:
		rate = maxFeeRate

	case rate < -maxFeeRate:
		rate = -maxFeeRate
	}

	// Calculate proportional component. To keep the integer math simple,
	// positive fees are rounded down while negative fees are rounded up.
	fee += rate * int64(amt) / feeRateParts

	return fee
}