graph/db: move FilterKnownChanIDs zombie logic up one layer

Here, we move the business logic in FilterKnownChanIDs from the CRUD
layer to the ChannelGraph layer. We also add a test for the logic.

graph/db/graph.go

@@ -1,6 +1,7 @@
 package graphdb
 
 import (
+	"errors"
 	"sync"
 	"time"
 
@@ -386,3 +387,55 @@ func (c *ChannelGraph) PruneGraphNodes() error {
 
 	return nil
 }
+
+// FilterKnownChanIDs takes a set of channel IDs and return the subset of chan
+// ID's that we don't know and are not known zombies of the passed set. In other
+// words, we perform a set difference of our set of chan ID's and the ones
+// passed in. This method can be used by callers to determine the set of
+// channels another peer knows of that we don't.
+func (c *ChannelGraph) FilterKnownChanIDs(chansInfo []ChannelUpdateInfo,
+	isZombieChan func(time.Time, time.Time) bool) ([]uint64, error) {
+
+	unknown, knownZombies, err := c.KVStore.FilterKnownChanIDs(chansInfo)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, info := range knownZombies {
+		// TODO(ziggie): Make sure that for the strict pruning case we
+		// compare the pubkeys and whether the right timestamp is not
+		// older than the `ChannelPruneExpiry`.
+		//
+		// NOTE: The timestamp data has no verification attached to it
+		// in the `ReplyChannelRange` msg so we are trusting this data
+		// at this point. However it is not critical because we are just
+		// removing the channel from the db when the timestamps are more
+		// recent. During the querying of the gossip msg verification
+		// happens as usual. However we should start punishing peers
+		// when they don't provide us honest data ?
+		isStillZombie := isZombieChan(
+			info.Node1UpdateTimestamp, info.Node2UpdateTimestamp,
+		)
+
+		if isStillZombie {
+			continue
+		}
+
+		// If we have marked it as a zombie but the latest update
+		// timestamps could bring it back from the dead, then we mark it
+		// alive, and we let it be added to the set of IDs to query our
+		// peer for.
+		err := c.KVStore.MarkEdgeLive(
+			info.ShortChannelID.ToUint64(),
+		)
+		// Since there is a chance that the edge could have been marked
+		// as "live" between the FilterKnownChanIDs call and the
+		// MarkEdgeLive call, we ignore the error if the edge is already
+		// marked as live.
+		if err != nil && !errors.Is(err, ErrZombieEdgeNotFound) {
+			return nil, err
+		}
+	}
+
+	return unknown, nil
+}