[#1680] morph/netmap: Pre-refactor processing of node states

New network status of storage nodes is going to be introduced. To
simplify the addition, it would be useful to prepare the code for this.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/morph/event/netmap/update_peer.go

@@ -12,10 +12,16 @@ import (
 	"github.com/nspcc-dev/neofs-node/pkg/morph/event"
 )
 
+// TODO: enum can become redundant after neofs-contract#270
+const (
+	_ int8 = iota
+	stateOnline
+)
+
 type UpdatePeer struct {
 	publicKey *keys.PublicKey
 
-	online bool
+	state int8 // state enum value
 
 	// For notary notifications only.
 	// Contains raw transactions of notary request.
@@ -26,7 +32,7 @@ type UpdatePeer struct {
 func (UpdatePeer) MorphEvent() {}
 
 func (s UpdatePeer) Online() bool {
-	return s.online
+	return s.state == stateOnline
 }
 
 func (s UpdatePeer) PublicKey() *keys.PublicKey {
@@ -78,7 +84,7 @@ func ParseUpdatePeer(e *state.ContainedNotificationEvent) (event.Event, error) {
 		return nil, fmt.Errorf("unsupported node state %d", st)
 	case int64(netmap.OfflineState):
 	case int64(netmap.OnlineState):
-		ev.online = true
+		ev.state = stateOnline
 	}
 
 	return ev, nil