loop/liquidity/liquidity.go

// Package liquidity is responsible for monitoring our node's liquidity. It
// allows setting of a liquidity rule which describes the desired liquidity
// balance on a per-channel basis.
//
// Swap suggestions are limited to channels that are not currently being used
// for a pending swap. If we are currently processing an unrestricted swap (ie,
// a loop out with no outgoing channel targets set or a loop in with no last
// hop set), we will not suggest any swaps because these swaps will shift the
// balances of our channels in ways we can't predict.
//
// Fee restrictions are placed on swap suggestions to ensure that we only
// suggest swaps that fit the configured fee preferences.
// - Sweep Fee Rate Limit: the maximum sat/vByte fee estimate for our sweep
//   transaction to confirm within our configured number of confirmations
//   that we will suggest swaps for.
// - Maximum Swap Fee PPM: the maximum server fee, expressed as parts per
//   million of the full swap amount
// - Maximum Routing Fee PPM: the maximum off-chain routing fees for the swap
//   invoice, expressed as parts per million of the swap amount.
// - Maximum Prepay Routing Fee PPM: the maximum off-chain routing fees for the
//   swap prepayment, expressed as parts per million of the prepay amount.
// - Maximum Prepay: the maximum now-show fee, expressed in satoshis. This
//   amount is only payable in the case where the swap server broadcasts a htlc
//   and the client fails to sweep the preimage.
// - Maximum miner fee: the maximum miner fee we are willing to pay to sweep the
//   on chain htlc. Note that the client will use current fee estimates to
//   sweep, so this value acts more as a sanity check in the case of a large fee
//   spike.
//
// The maximum fee per-swap is calculated as follows:
// (swap amount * serverPPM/1e6) + miner fee + (swap amount * routingPPM/1e6)
// + (prepay amount * prepayPPM/1e6).
package liquidity

import (
	"context"
	"errors"
	"fmt"
	"sort"
	"sync"
	"time"

	"github.com/btcsuite/btcd/btcutil"
	"github.com/lightninglabs/lndclient"
	"github.com/lightninglabs/loop"
	"github.com/lightninglabs/loop/labels"
	"github.com/lightninglabs/loop/loopdb"
	"github.com/lightninglabs/loop/swap"
	"github.com/lightningnetwork/lnd/clock"
	"github.com/lightningnetwork/lnd/funding"
	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
	"github.com/lightningnetwork/lnd/lnwire"
	"github.com/lightningnetwork/lnd/routing/route"
	"github.com/lightningnetwork/lnd/ticker"
	"google.golang.org/protobuf/proto"

	clientrpc "github.com/lightninglabs/loop/looprpc"
)

const (
	// defaultFailureBackoff is the default amount of time we backoff if
	// a channel is part of a temporarily failed swap.
	defaultFailureBackoff = time.Hour * 24

	// defaultConfTarget is the default sweep target we use for loop outs.
	// We get our inbound liquidity quickly using preimage push, so we can
	// use a long conf target without worrying about ux impact.
	defaultConfTarget = 100

	// FeeBase is the base that we use to express fees.
	FeeBase = 1e6

	// defaultMaxInFlight is the default number of in-flight automatically
	// dispatched swaps we allow. Note that this does not enable automated
	// swaps itself (because we want non-zero values to be expressed in
	// suggestions as a dry-run).
	defaultMaxInFlight = 1

	// DefaultAutoloopTicker is the default amount of time between automated
	// swap checks.
	DefaultAutoloopTicker = time.Minute * 10

	// autoloopSwapInitiator is the value we send in the initiator field of
	// a swap request when issuing an automatic swap.
	autoloopSwapInitiator = "autoloop"

	// We use a static fee rate to estimate our sweep fee, because we
	// can't realistically estimate what our fee estimate will be by the
	// time we reach timeout. We set this to a high estimate so that we can
	// account for worst-case fees, (1250 * 4 / 1000) = 50 sat/byte.
	defaultLoopInSweepFee = chainfee.SatPerKWeight(1250)
)

var (
	// defaultHtlcConfTarget is the default confirmation target we use for
	// loop in swap htlcs, set to the same default at the client.
	defaultHtlcConfTarget = loop.DefaultHtlcConfTarget

	// defaultBudget is the default autoloop budget we set. This budget will
	// only be used for automatically dispatched swaps if autoloop is
	// explicitly enabled, so we are happy to set a non-zero value here. The
	// amount chosen simply uses the current defaults to provide budget for
	// a single swap. We don't have a swap amount so we just use our max
	// funding amount.
	defaultBudget = ppmToSat(funding.MaxBtcFundingAmount, defaultFeePPM)

	// ErrZeroChannelID is returned if we get a rule for a 0 channel ID.
	ErrZeroChannelID = fmt.Errorf("zero channel ID not allowed")

	// ErrNegativeBudget is returned if a negative swap budget is set.
	ErrNegativeBudget = errors.New("swap budget must be >= 0")

	// ErrZeroInFlight is returned is a zero in flight swaps value is set.
	ErrZeroInFlight = errors.New("max in flight swaps must be >=0")

	// ErrMinimumExceedsMaximumAmt is returned when the minimum configured
	// swap amount is more than the maximum.
	ErrMinimumExceedsMaximumAmt = errors.New("minimum swap amount " +
		"exceeds maximum")

	// ErrMaxExceedsServer is returned if the maximum swap amount set is
	// more than the server offers.
	ErrMaxExceedsServer = errors.New("maximum swap amount is more than " +
		"server maximum")

	// ErrMinLessThanServer is returned if the minimum swap amount set is
	// less than the server minimum.
	ErrMinLessThanServer = errors.New("minimum swap amount is less than " +
		"server minimum")

	// ErrNoRules is returned when no rules are set for swap suggestions.
	ErrNoRules = errors.New("no rules set for autoloop")

	// ErrExclusiveRules is returned when a set of rules that may not be
	// set together are specified.
	ErrExclusiveRules = errors.New("channel and peer rules must be " +
		"exclusive")
)

// Config contains the external functionality required to run the
// liquidity manager.
type Config struct {
	// AutoloopTicker determines how often we should check whether we want
	// to dispatch an automated swap. We use a force ticker so that we can
	// trigger autoloop in itests.
	AutoloopTicker *ticker.Force

	// Restrictions returns the restrictions that the server applies to
	// swaps.
	Restrictions func(ctx context.Context, swapType swap.Type) (
		*Restrictions, error)

	// Lnd provides us with access to lnd's rpc servers.
	Lnd *lndclient.LndServices

	// ListLoopOut returns all of the loop our swaps stored on disk.
	ListLoopOut func() ([]*loopdb.LoopOut, error)

	// ListLoopIn returns all of the loop in swaps stored on disk.
	ListLoopIn func() ([]*loopdb.LoopIn, error)

	// LoopOutQuote gets swap fee, estimated miner fee and prepay amount for
	// a loop out swap.
	LoopOutQuote func(ctx context.Context,
		request *loop.LoopOutQuoteRequest) (*loop.LoopOutQuote, error)

	// LoopInQuote provides a quote for a loop in swap.
	LoopInQuote func(ctx context.Context,
		request *loop.LoopInQuoteRequest) (*loop.LoopInQuote, error)

	// LoopOut dispatches a loop out.
	LoopOut func(ctx context.Context, request *loop.OutRequest) (
		*loop.LoopOutSwapInfo, error)

	// LoopIn dispatches a loop in swap.
	LoopIn func(ctx context.Context,
		request *loop.LoopInRequest) (*loop.LoopInSwapInfo, error)

	// Clock allows easy mocking of time in unit tests.
	Clock clock.Clock

	// MinimumConfirmations is the minimum number of confirmations we allow
	// setting for sweep target.
	MinimumConfirmations int32

	// PutLiquidityParams writes the serialized `Parameters` into db.
	//
	// NOTE: the params are encoded using `proto.Marshal` over an RPC
	// request.
	PutLiquidityParams func(params []byte) error

	// FetchLiquidityParams reads the serialized `Parameters` from db.
	//
	// NOTE: the params are decoded using `proto.Unmarshal` over a
	// serialized RPC request.
	FetchLiquidityParams func() ([]byte, error)
}

// Manager contains a set of desired liquidity rules for our channel
// balances.
type Manager struct {
	// cfg contains the external functionality we require to determine our
	// current liquidity balance.
	cfg *Config

	// params is the set of parameters we are currently using. These may be
	// updated at runtime.
	params Parameters

	// paramsLock is a lock for our current set of parameters.
	paramsLock sync.Mutex
}

// Run periodically checks whether we should automatically dispatch a loop out.
// We run this loop even if automated swaps are not currently enabled rather
// than managing starting and stopping the ticker as our parameters are updated.
func (m *Manager) Run(ctx context.Context) error {
	m.cfg.AutoloopTicker.Resume()
	defer m.cfg.AutoloopTicker.Stop()

	// Before we start the main loop, load the params from db.
	req, err := m.loadParams()
	if err != nil {
		return err
	}

	// Set the params if there's one.
	if req != nil {
		if err := m.SetParameters(ctx, req); err != nil {
			return err
		}
	}

	for {
		select {
		case <-m.cfg.AutoloopTicker.Ticks():
			err := m.autoloop(ctx)
			switch err {
			case ErrNoRules:
				log.Debugf("No rules configured for autoloop")

			case nil:

			default:
				log.Errorf("autoloop failed: %v", err)
			}

		case <-ctx.Done():
			return ctx.Err()
		}
	}
}

// NewManager creates a liquidity manager which has no rules set.
func NewManager(cfg *Config) *Manager {
	return &Manager{
		cfg:    cfg,
		params: defaultParameters,
	}
}

// GetParameters returns a copy of our current parameters.
func (m *Manager) GetParameters() Parameters {
	m.paramsLock.Lock()
	defer m.paramsLock.Unlock()

	return cloneParameters(m.params)
}

// SetParameters takes an RPC request and calls the internal method to set
// parameters for the manager.
func (m *Manager) SetParameters(ctx context.Context,
	req *clientrpc.LiquidityParameters) error {

	params, err := rpcToParameters(req)
	if err != nil {
		return err
	}

	if err := m.setParameters(ctx, *params); err != nil {
		return err
	}

	// Save the params on disk.
	//
	// NOTE: alternatively we can save the bytes in memory and persist them
	// on disk during shutdown to save us some IO cost from hitting the db.
	// Since setting params is NOT a frequent action, it's should put
	// little pressure on our db. Only when performance becomes an issue,
	// we can then apply the alternative.
	return m.saveParams(req)
}

// SetParameters updates our current set of parameters if the new parameters
// provided are valid.
func (m *Manager) setParameters(ctx context.Context,
	params Parameters) error {

	restrictions, err := m.cfg.Restrictions(ctx, swap.TypeOut)
	if err != nil {
		return err
	}

	channels, err := m.cfg.Lnd.Client.ListChannels(ctx, false, false)
	if err != nil {
		return err
	}

	err = params.validate(
		m.cfg.MinimumConfirmations, channels, restrictions,
	)
	if err != nil {
		return err
	}

	m.paramsLock.Lock()
	defer m.paramsLock.Unlock()

	m.params = cloneParameters(params)

	return nil
}

// saveParams marshals an RPC request and saves it to db.
func (m *Manager) saveParams(req proto.Message) error {
	// Marshal the params.
	paramsBytes, err := proto.Marshal(req)
	if err != nil {
		return err
	}

	// Save the params on disk.
	if err := m.cfg.PutLiquidityParams(paramsBytes); err != nil {
		return fmt.Errorf("failed to save params: %v", err)
	}

	return nil
}

// loadParams unmarshals a serialized RPC request from db and returns the RPC
// request.
func (m *Manager) loadParams() (*clientrpc.LiquidityParameters, error) {
	paramsBytes, err := m.cfg.FetchLiquidityParams()
	if err != nil {
		return nil, fmt.Errorf("failed to read params: %v", err)
	}

	// Return early if there's nothing saved.
	if paramsBytes == nil {
		return nil, nil
	}

	// Unmarshal the params.
	req := &clientrpc.LiquidityParameters{}
	err = proto.Unmarshal(paramsBytes, req)
	if err != nil {
		return nil, fmt.Errorf("failed to unmarshal params: %v", err)
	}

	return req, nil
}

// autoloop gets a set of suggested swaps and dispatches them automatically if
// we have automated looping enabled.
func (m *Manager) autoloop(ctx context.Context) error {
	suggestion, err := m.SuggestSwaps(ctx, true)
	if err != nil {
		return err
	}

	for _, swap := range suggestion.OutSwaps {
		// If we don't actually have dispatch of swaps enabled, log
		// suggestions.
		if !m.params.Autoloop {
			log.Debugf("recommended autoloop out: %v sats over "+
				"%v", swap.Amount, swap.OutgoingChanSet)

			continue
		}

		// Create a copy of our range var so that we can reference it.
		swap := swap
		loopOut, err := m.cfg.LoopOut(ctx, &swap)
		if err != nil {
			return err
		}

		log.Infof("loop out automatically dispatched: hash: %v, "+
			"address: %v", loopOut.SwapHash, loopOut.HtlcAddress)
	}

	for _, in := range suggestion.InSwaps {
		// If we don't actually have dispatch of swaps enabled, log
		// suggestions.
		if !m.params.Autoloop {
			log.Debugf("recommended autoloop in: %v sats over "+
				"%v", in.Amount, in.LastHop)

			continue
		}

		in := in
		loopIn, err := m.cfg.LoopIn(ctx, &in)
		if err != nil {
			return err
		}

		log.Infof("loop in automatically dispatched: hash: %v, "+
			"address: np2wsh(%v), p2wsh(%v), p2tr(%v)",
			loopIn.SwapHash, loopIn.HtlcAddressNP2WSH,
			loopIn.HtlcAddressP2WSH, loopIn.HtlcAddressP2TR)
	}

	return nil
}

// ForceAutoLoop force-ticks our auto-out ticker.
func (m *Manager) ForceAutoLoop(ctx context.Context) error {
	select {
	case m.cfg.AutoloopTicker.Force <- m.cfg.Clock.Now():
		return nil

	case <-ctx.Done():
		return ctx.Err()
	}
}

// Suggestions provides a set of suggested swaps, and the set of channels that
// were excluded from consideration.
type Suggestions struct {
	// OutSwaps is the set of loop out swaps that we suggest executing.
	OutSwaps []loop.OutRequest

	// InSwaps is the set of loop in swaps that we suggest executing.
	InSwaps []loop.LoopInRequest

	// DisqualifiedChans maps the set of channels that we do not recommend
	// swaps on to the reason that we did not recommend a swap.
	DisqualifiedChans map[lnwire.ShortChannelID]Reason

	// Disqualified peers maps the set of peers that we do not recommend
	// swaps for to the reason that they were excluded.
	DisqualifiedPeers map[route.Vertex]Reason
}

func newSuggestions() *Suggestions {
	return &Suggestions{
		DisqualifiedChans: make(map[lnwire.ShortChannelID]Reason),
		DisqualifiedPeers: make(map[route.Vertex]Reason),
	}
}

func (s *Suggestions) addSwap(swap swapSuggestion) error {
	switch t := swap.(type) {
	case *loopOutSwapSuggestion:
		s.OutSwaps = append(s.OutSwaps, t.OutRequest)

	case *loopInSwapSuggestion:
		s.InSwaps = append(s.InSwaps, t.LoopInRequest)

	default:
		return fmt.Errorf("unexpected swap type: %T", swap)
	}

	return nil
}

// singleReasonSuggestion is a helper function which returns a set of
// suggestions where all of our rules are disqualified due to a reason that
// applies to all of them (such as being out of budget).
func (m *Manager) singleReasonSuggestion(reason Reason) *Suggestions {
	resp := newSuggestions()

	for id := range m.params.ChannelRules {
		resp.DisqualifiedChans[id] = reason
	}

	for peer := range m.params.PeerRules {
		resp.DisqualifiedPeers[peer] = reason
	}

	return resp
}

// SuggestSwaps returns a set of swap suggestions based on our current liquidity
// balance for the set of rules configured for the manager, failing if there are
// no rules set. It takes an autoloop boolean that indicates whether the
// suggestions are being used for our internal autolooper. This boolean is used
// to determine the information we add to our swap suggestion and whether we
// return any suggestions.
func (m *Manager) SuggestSwaps(ctx context.Context, autoloop bool) (
	*Suggestions, error) {

	m.paramsLock.Lock()
	defer m.paramsLock.Unlock()

	// If we have no rules set, exit early to avoid unnecessary calls to
	// lnd and the server.
	if !m.params.haveRules() {
		return nil, ErrNoRules
	}

	// If our start date is in the future, we interpret this as meaning that
	// we should start using our budget at this date. This means that we
	// have no budget for the present, so we just return.
	if m.params.AutoFeeStartDate.After(m.cfg.Clock.Now()) {
		log.Debugf("autoloop fee budget start time: %v is in "+
			"the future", m.params.AutoFeeStartDate)

		return m.singleReasonSuggestion(ReasonBudgetNotStarted), nil
	}

	// Get restrictions placed on swaps by the server.
	outRestrictions, err := m.getSwapRestrictions(ctx, swap.TypeOut)
	if err != nil {
		return nil, err
	}

	inRestrictions, err := m.getSwapRestrictions(ctx, swap.TypeIn)
	if err != nil {
		return nil, err
	}

	// List our current set of swaps so that we can determine which channels
	// are already being utilized by swaps. Note that these calls may race
	// with manual initiation of swaps.
	loopOut, err := m.cfg.ListLoopOut()
	if err != nil {
		return nil, err
	}

	loopIn, err := m.cfg.ListLoopIn()
	if err != nil {
		return nil, err
	}

	// Get a summary of our existing swaps so that we can check our autoloop
	// budget.
	summary, err := m.checkExistingAutoLoops(ctx, loopOut, loopIn)
	if err != nil {
		return nil, err
	}

	if summary.totalFees() >= m.params.AutoFeeBudget {
		log.Debugf("autoloop fee budget: %v exhausted, %v spent on "+
			"completed swaps, %v reserved for ongoing swaps "+
			"(upper limit)",
			m.params.AutoFeeBudget, summary.spentFees,
			summary.pendingFees)

		return m.singleReasonSuggestion(ReasonBudgetElapsed), nil
	}

	// If we have already reached our total allowed number of in flight
	// swaps, we do not suggest any more at the moment.
	allowedSwaps := m.params.MaxAutoInFlight - summary.inFlightCount
	if allowedSwaps <= 0 {
		log.Debugf("%v autoloops allowed, %v in flight",
			m.params.MaxAutoInFlight, summary.inFlightCount)

		return m.singleReasonSuggestion(ReasonInFlight), nil
	}

	channels, err := m.cfg.Lnd.Client.ListChannels(ctx, false, false)
	if err != nil {
		return nil, err
	}

	// Collect a map of channel IDs to peer pubkeys, and a set of per-peer
	// balances which we will use for peer-level liquidity rules.
	channelPeers := make(map[uint64]route.Vertex)
	peerChannels := make(map[route.Vertex]*balances)
	for _, channel := range channels {
		channelPeers[channel.ChannelID] = channel.PubKeyBytes

		bal, ok := peerChannels[channel.PubKeyBytes]
		if !ok {
			bal = &balances{}
		}

		chanID := lnwire.NewShortChanIDFromInt(channel.ChannelID)
		bal.channels = append(bal.channels, chanID)
		bal.capacity += channel.Capacity
		bal.incoming += channel.RemoteBalance
		bal.outgoing += channel.LocalBalance
		bal.pubkey = channel.PubKeyBytes

		peerChannels[channel.PubKeyBytes] = bal
	}

	// Get a summary of the channels and peers that are not eligible due
	// to ongoing swaps.
	traffic := m.currentSwapTraffic(loopOut, loopIn)

	var (
		suggestions []swapSuggestion
		resp        = newSuggestions()
	)

	for peer, balances := range peerChannels {
		rule, haveRule := m.params.PeerRules[peer]
		if !haveRule {
			continue
		}

		suggestion, err := m.suggestSwap(
			ctx, traffic, balances, rule, outRestrictions,
			inRestrictions, autoloop,
		)
		var reasonErr *reasonError
		if errors.As(err, &reasonErr) {
			resp.DisqualifiedPeers[peer] = reasonErr.reason
			continue
		}

		if err != nil {
			return nil, err
		}

		suggestions = append(suggestions, suggestion)
	}

	for _, channel := range channels {
		balance := newBalances(channel)

		channelID := lnwire.NewShortChanIDFromInt(channel.ChannelID)
		rule, ok := m.params.ChannelRules[channelID]
		if !ok {
			continue
		}

		suggestion, err := m.suggestSwap(
			ctx, traffic, balance, rule, outRestrictions,
			inRestrictions, autoloop,
		)

		var reasonErr *reasonError
		if errors.As(err, &reasonErr) {
			resp.DisqualifiedChans[channelID] = reasonErr.reason
			continue
		}

		if err != nil {
			return nil, err
		}

		suggestions = append(suggestions, suggestion)
	}

	// If we have no swaps to execute after we have applied all of our
	// limits, just return our set of disqualified swaps.
	if len(suggestions) == 0 {
		return resp, nil
	}

	// Sort suggestions by amount in descending order.
	sort.SliceStable(suggestions, func(i, j int) bool {
		return suggestions[i].amount() > suggestions[j].amount()
	})

	// Run through our suggested swaps in descending order of amount and
	// return all of the swaps which will fit within our remaining budget.
	available := m.params.AutoFeeBudget - summary.totalFees()

	// setReason is a helper that adds a swap's channels to our disqualified
	// list with the reason provided.
	setReason := func(reason Reason, swap swapSuggestion) {
		for _, peer := range swap.peers(channelPeers) {
			_, ok := m.params.PeerRules[peer]
			if !ok {
				continue
			}

			resp.DisqualifiedPeers[peer] = reason
		}

		for _, channel := range swap.channels() {
			_, ok := m.params.ChannelRules[channel]
			if !ok {
				continue
			}

			resp.DisqualifiedChans[channel] = reason
		}
	}

	for _, swap := range suggestions {
		swap := swap

		// If we do not have enough funds available, or we hit our
		// in flight limit, we record this value for the rest of the
		// swaps.
		var reason Reason
		switch {
		case available == 0:
			reason = ReasonBudgetInsufficient

		case len(resp.OutSwaps) == allowedSwaps:
			reason = ReasonInFlight
		}

		if reason != ReasonNone {
			setReason(reason, swap)
			continue
		}

		fees := swap.fees()

		// If the maximum fee we expect our swap to use is less than the
		// amount we have available, we add it to our set of swaps that
		// fall within the budget and decrement our available amount.
		if fees <= available {
			available -= fees

			if err := resp.addSwap(swap); err != nil {
				return nil, err
			}
		} else {
			setReason(ReasonBudgetInsufficient, swap)
		}
	}

	return resp, nil
}

// suggestSwap checks whether we can currently perform a swap, and creates a
// swap request for the rule provided.
func (m *Manager) suggestSwap(ctx context.Context, traffic *swapTraffic,
	balance *balances, rule *SwapRule, outRestrictions *Restrictions,
	inRestrictions *Restrictions, autoloop bool) (swapSuggestion, error) {

	var (
		builder      swapBuilder
		restrictions *Restrictions
	)

	// Get an appropriate builder and set of restrictions based on our swap
	// type.
	switch rule.Type {
	case swap.TypeOut:
		builder = newLoopOutBuilder(m.cfg)
		restrictions = outRestrictions

	case swap.TypeIn:
		builder = newLoopInBuilder(m.cfg)
		restrictions = inRestrictions

	default:
		return nil, fmt.Errorf("unsupported swap type: %v", rule.Type)
	}

	// Before we get any swap suggestions, we check what the current fee
	// estimate is to sweep within our target number of confirmations. If
	// This fee exceeds the fee limit we have set, we will not suggest any
	// swaps at present.
	if err := builder.maySwap(ctx, m.params); err != nil {
		return nil, err
	}

	// First, check whether this peer/channel combination is already in use
	// for our swap.
	err := builder.inUse(traffic, balance.pubkey, balance.channels)
	if err != nil {
		return nil, err
	}

	// Next, get the amount that we need to swap for this entity, skipping
	// over it if no change in liquidity is required.
	amount := rule.swapAmount(balance, restrictions, rule.Type)
	if amount == 0 {
		return nil, newReasonError(ReasonLiquidityOk)
	}

	return builder.buildSwap(
		ctx, balance.pubkey, balance.channels, amount, autoloop,
		m.params,
	)
}

// getSwapRestrictions queries the server for its latest swap size restrictions,
// validates client restrictions (if present) against these values and merges
// the client's custom requirements with the server's limits to produce a single
// set of limitations for our swap.
func (m *Manager) getSwapRestrictions(ctx context.Context, swapType swap.Type) (
	*Restrictions, error) {

	restrictions, err := m.cfg.Restrictions(ctx, swapType)
	if err != nil {
		return nil, err
	}

	// It is possible that the server has updated its restrictions since
	// we validated our client restrictions, so we validate again to ensure
	// that our restrictions are within the server's bounds.
	err = validateRestrictions(restrictions, &m.params.ClientRestrictions)
	if err != nil {
		return nil, err
	}

	// If our minimum is more than the server's minimum, we set it.
	if m.params.ClientRestrictions.Minimum > restrictions.Minimum {
		restrictions.Minimum = m.params.ClientRestrictions.Minimum
	}

	// If our maximum set and is less than the server's maximum, we set it.
	if m.params.ClientRestrictions.Maximum != 0 &&
		m.params.ClientRestrictions.Maximum < restrictions.Maximum {

		restrictions.Maximum = m.params.ClientRestrictions.Maximum
	}

	return restrictions, nil
}

// worstCaseOutFees calculates the largest possible fees for a loop out swap,
// comparing the fees for a successful swap to the cost when the client pays
// the prepay because they failed to sweep the on chain htlc. This is unlikely,
// because we expect clients to be online to sweep, but we want to account for
// every outcome so we include it.
func worstCaseOutFees(prepayRouting, swapRouting, swapFee, minerFee,
	prepayAmount btcutil.Amount) btcutil.Amount {

	var (
		successFees = prepayRouting + minerFee + swapFee + swapRouting
		noShowFees  = prepayRouting + prepayAmount
	)

	if noShowFees > successFees {
		return noShowFees
	}

	return successFees
}

// existingAutoLoopSummary provides a summary of the existing autoloops which
// were dispatched during our current budget period.
type existingAutoLoopSummary struct {
	// spentFees is the amount we have spent on completed swaps.
	spentFees btcutil.Amount

	// pendingFees is the worst-case amount of fees we could spend on in
	// flight autoloops.
	pendingFees btcutil.Amount

	// inFlightCount is the total number of automated swaps that are
	// currently in flight. Note that this may race with swap completion,
	// but not with initiation of new automated swaps, this is ok, because
	// it can only lead to dispatching fewer swaps than we could have (not
	// too many).
	inFlightCount int
}

// totalFees returns the total amount of fees that automatically dispatched
// swaps may consume.
func (e *existingAutoLoopSummary) totalFees() btcutil.Amount {
	return e.spentFees + e.pendingFees
}

// checkExistingAutoLoops calculates the total amount that has been spent by
// automatically dispatched swaps that have completed, and the worst-case fee
// total for our set of ongoing, automatically dispatched swaps as well as a
// current in-flight count.
func (m *Manager) checkExistingAutoLoops(ctx context.Context,
	loopOuts []*loopdb.LoopOut, loopIns []*loopdb.LoopIn) (
	*existingAutoLoopSummary, error) {

	var summary existingAutoLoopSummary

	for _, out := range loopOuts {
		if out.Contract.Label != labels.AutoloopLabel(swap.TypeOut) {
			continue
		}

		// If we have a pending swap, we are uncertain of the fees that
		// it will end up paying. We use the worst-case estimate based
		// on the maximum values we set for each fee category. This will
		// likely over-estimate our fees (because we probably won't
		// spend our maximum miner amount). If a swap is not pending,
		// it has succeeded or failed so we just record our actual fees
		// for the swap provided that the swap completed after our
		// budget start date.
		if out.State().State.Type() == loopdb.StateTypePending {
			summary.inFlightCount++

			prepay, err := m.cfg.Lnd.Client.DecodePaymentRequest(
				ctx, out.Contract.PrepayInvoice,
			)
			if err != nil {
				return nil, err
			}

			summary.pendingFees += worstCaseOutFees(
				out.Contract.MaxPrepayRoutingFee,
				out.Contract.MaxSwapRoutingFee,
				out.Contract.MaxSwapFee,
				out.Contract.MaxMinerFee,
				mSatToSatoshis(prepay.Value),
			)
		} else if !out.LastUpdateTime().Before(m.params.AutoFeeStartDate) {
			summary.spentFees += out.State().Cost.Total()
		}
	}

	for _, in := range loopIns {
		if in.Contract.Label != labels.AutoloopLabel(swap.TypeIn) {
			continue
		}

		pending := in.State().State.Type() == loopdb.StateTypePending
		inBudget := !in.LastUpdateTime().Before(m.params.AutoFeeStartDate)

		// If an autoloop is in a pending state, we always count it in
		// our current budget, and record the worst-case fees for it,
		// because we do not know how it will resolve.
		if pending {
			summary.inFlightCount++
			summary.pendingFees += worstCaseInFees(
				in.Contract.MaxMinerFee, in.Contract.MaxSwapFee,
				defaultLoopInSweepFee,
			)
		} else if inBudget {
			summary.spentFees += in.State().Cost.Total()
		}
	}

	return &summary, nil
}

// currentSwapTraffic examines our existing swaps and returns a summary of the
// current activity which can be used to determine whether we should perform
// any swaps.
func (m *Manager) currentSwapTraffic(loopOut []*loopdb.LoopOut,
	loopIn []*loopdb.LoopIn) *swapTraffic {

	traffic := newSwapTraffic()

	// Failure cutoff is the most recent failure timestamp we will still
	// consider a channel eligible. Any channels involved in swaps that have
	// failed since this point will not be considered.
	failureCutoff := m.cfg.Clock.Now().Add(m.params.FailureBackOff * -1)

	for _, out := range loopOut {
		var (
			state   = out.State().State
			chanSet = out.Contract.OutgoingChanSet
		)

		// If a loop out swap failed due to off chain payment after our
		// failure cutoff, we add all of its channels to a set of
		// recently failed channels. It is possible that not all of
		// these channels were used for the swap, but we play it safe
		// and back off for all of them.
		//
		// We only backoff for off temporary failures. In the case of
		// chain payment failures, our swap failed to route and we do
		// not want to repeatedly try to route through bad channels
		// which remain unbalanced because they cannot route a swap, so
		// we backoff.
		if state == loopdb.StateFailOffchainPayments {
			failedAt := out.LastUpdate().Time

			if failedAt.After(failureCutoff) {
				for _, id := range chanSet {
					chanID := lnwire.NewShortChanIDFromInt(
						id,
					)

					traffic.failedLoopOut[chanID] = failedAt
				}
			}
		}

		// Skip completed swaps, they can't affect our channel balances.
		// Swaps that fail temporarily are considered to be in a pending
		// state, so we will also check that channels being used by
		// these swaps. This is important, because a temporarily failed
		// swap could be re-dispatched on restart, affecting our
		// balances.
		if state.Type() != loopdb.StateTypePending {
			continue
		}

		for _, id := range chanSet {
			chanID := lnwire.NewShortChanIDFromInt(id)
			traffic.ongoingLoopOut[chanID] = true
		}
	}

	for _, in := range loopIn {
		// Skip over swaps that may come through any peer.
		if in.Contract.LastHop == nil {
			continue
		}

		pubkey := *in.Contract.LastHop

		switch {
		// Include any pending swaps in our ongoing set of swaps.
		case in.State().State.Type() == loopdb.StateTypePending:
			traffic.ongoingLoopIn[pubkey] = true

		// If a swap failed with an on-chain timeout, the server could
		// not route to us. We add it to our backoff list so that
		// there's some time for routing conditions to improve.
		case in.State().State == loopdb.StateFailTimeout:
			failedAt := in.LastUpdate().Time

			if failedAt.After(failureCutoff) {
				traffic.failedLoopIn[pubkey] = failedAt
			}
		}
	}

	return traffic
}

// swapTraffic contains a summary of our current and previously failed swaps.
type swapTraffic struct {
	ongoingLoopOut map[lnwire.ShortChannelID]bool
	ongoingLoopIn  map[route.Vertex]bool
	failedLoopOut  map[lnwire.ShortChannelID]time.Time
	failedLoopIn   map[route.Vertex]time.Time
}

func newSwapTraffic() *swapTraffic {
	return &swapTraffic{
		ongoingLoopOut: make(map[lnwire.ShortChannelID]bool),
		ongoingLoopIn:  make(map[route.Vertex]bool),
		failedLoopOut:  make(map[lnwire.ShortChannelID]time.Time),
		failedLoopIn:   make(map[route.Vertex]time.Time),
	}
}

// satPerKwToSatPerVByte converts sat per kWeight to sat per vByte.
func satPerKwToSatPerVByte(satPerKw chainfee.SatPerKWeight) int64 {
	return int64(satPerKw.FeePerKVByte() / 1000)
}

// ppmToSat takes an amount and a measure of parts per million for the amount
// and returns the amount that the ppm represents.
func ppmToSat(amount btcutil.Amount, ppm uint64) btcutil.Amount {
	return btcutil.Amount(uint64(amount) * ppm / FeeBase)
}

func mSatToSatoshis(amount lnwire.MilliSatoshi) btcutil.Amount {
	return btcutil.Amount(amount / 1000)
}