liquidity: refactor eligible channels logic to ineligible channels

This commit switches up our eligible channels logic to rather return
a struct containing information about our current swap traffic. This
change is made in preparation for returning reasons indicating why we
did not perform a swap for a specific channel - when we only return
eligible swaps, we lose the information about why all the excluded
channels weren't used.

liquidity/liquidity.go

@@ -652,25 +652,32 @@ func (m *Manager) SuggestSwaps(ctx context.Context, autoloop bool) (
 		return nil, nil
 	}
 
-	eligible, err := m.getEligibleChannels(ctx, loopOut, loopIn)
+	channels, err := m.cfg.Lnd.Client.ListChannels(ctx)
 	if err != nil {
 		return nil, err
 	}
 
+	// Get a summary of the channels and peers that are not eligible due
+	// to ongoing swaps.
+	traffic := m.currentSwapTraffic(loopOut, loopIn)
+
 	var suggestions []loop.OutRequest
-	for _, channel := range eligible {
-		channelID := lnwire.NewShortChanIDFromInt(channel.ChannelID)
-		rule, ok := m.params.ChannelRules[channelID]
+
+	for _, channel := range channels {
+		balance := newBalances(channel)
+
+		rule, ok := m.params.ChannelRules[balance.channelID]
 		if !ok {
 			continue
 		}
 
-		balance := newBalances(channel)
-
-		suggestion := rule.suggestSwap(balance, restrictions)
+		if !traffic.maySwap(channel.PubKeyBytes, balance.channelID) {
+			continue
+		}
 
 		// We can have nil suggestions in the case where no action is
 		// required, so we skip over them.
+		suggestion := rule.suggestSwap(balance, restrictions)
 		if suggestion == nil {
 			continue
 		}
@@ -928,17 +935,13 @@ func (m *Manager) checkExistingAutoLoops(ctx context.Context,
 	return &summary, nil
 }
 
-// getEligibleChannels takes lists of our existing loop out and in swaps, and
-// gets a list of channels that are not currently being utilized for a swap.
-func (m *Manager) getEligibleChannels(ctx context.Context,
-	loopOut []*loopdb.LoopOut, loopIn []*loopdb.LoopIn) (
-	[]lndclient.ChannelInfo, error) {
+// 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 {
 
-	var (
-		existingOut = make(map[lnwire.ShortChannelID]bool)
-		existingIn  = make(map[route.Vertex]bool)
-		failedOut   = make(map[lnwire.ShortChannelID]time.Time)
-	)
+	traffic := newSwapTraffic()
 
 	// Failure cutoff is the most recent failure timestamp we will still
 	// consider a channel eligible. Any channels involved in swaps that have
@@ -971,7 +974,7 @@ func (m *Manager) getEligibleChannels(ctx context.Context,
 						id,
 					)
 
-					failedOut[chanID] = failedAt
+					traffic.failedLoopOut[chanID] = failedAt
 				}
 			}
 		}
@@ -988,7 +991,7 @@ func (m *Manager) getEligibleChannels(ctx context.Context,
 
 		for _, id := range chanSet {
 			chanID := lnwire.NewShortChanIDFromInt(id)
-			existingOut[chanID] = true
+			traffic.ongoingLoopOut[chanID] = true
 		}
 	}
 
@@ -1003,51 +1006,55 @@ func (m *Manager) getEligibleChannels(ctx context.Context,
 			continue
 		}
 
-		existingIn[*in.Contract.LastHop] = true
+		traffic.ongoingLoopIn[*in.Contract.LastHop] = true
 	}
 
-	channels, err := m.cfg.Lnd.Client.ListChannels(ctx)
-	if err != nil {
-		return nil, err
-	}
+	return traffic
+}
 
-	// Run through our set of channels and skip over any channels that
-	// are currently being utilized by a restricted swap (where restricted
-	// means that a loop out limited channels, or a loop in limited last
-	// hop).
-	var eligible []lndclient.ChannelInfo
-	for _, channel := range channels {
-		shortID := lnwire.NewShortChanIDFromInt(channel.ChannelID)
+// 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
+}
 
-		lastFail, recentFail := failedOut[shortID]
-		if recentFail {
-			log.Debugf("Channel: %v not eligible for "+
-				"suggestions, was part of a failed swap at: %v",
-				channel.ChannelID, lastFail)
+func newSwapTraffic() *swapTraffic {
+	return &swapTraffic{
+		ongoingLoopOut: make(map[lnwire.ShortChannelID]bool),
+		ongoingLoopIn:  make(map[route.Vertex]bool),
+		failedLoopOut:  make(map[lnwire.ShortChannelID]time.Time),
+	}
+}
 
-			continue
-		}
+// maySwap returns a boolean that indicates whether we may perform a swap for a
+// peer and its set of channels.
+func (s *swapTraffic) maySwap(peer route.Vertex,
+	chanID lnwire.ShortChannelID) bool {
 
-		if existingOut[shortID] {
-			log.Debugf("Channel: %v not eligible for "+
-				"suggestions, ongoing loop out utilizing "+
-				"channel", channel.ChannelID)
+	lastFail, recentFail := s.failedLoopOut[chanID]
+	if recentFail {
+		log.Debugf("Channel: %v not eligible for suggestions, was "+
+			"part of a failed swap at: %v", chanID, lastFail)
 
-			continue
-		}
+		return false
+	}
 
-		if existingIn[channel.PubKeyBytes] {
-			log.Debugf("Channel: %v not eligible for "+
-				"suggestions, ongoing loop in utilizing "+
-				"peer", channel.ChannelID)
+	if s.ongoingLoopOut[chanID] {
+		log.Debugf("Channel: %v not eligible for suggestions, "+
+			"ongoing loop out utilizing channel", chanID)
 
-			continue
-		}
+		return false
+	}
+
+	if s.ongoingLoopIn[peer] {
+		log.Debugf("Peer: %x not eligible for suggestions ongoing "+
+			"loop in utilizing peer", peer)
 
-		eligible = append(eligible, channel)
+		return false
 	}
 
-	return eligible, nil
+	return true
 }
 
 // checkFeeLimits takes a set of fees for a swap and checks whether they exceed