Add basic application framework and example application to show interaction between events an NBI

Depends on:

• !340 (merged)
• !344 (merged)
• !349 (merged)
• !342 (merged)

controller/topology/topologyService.go

@@ -2,6 +2,8 @@ package topology
 
 import (
 	"code.fbi.h-da.de/danet/gosdn/controller/topology/links"
+	"code.fbi.h-da.de/danet/gosdn/controller/topology/nodes"
+	"code.fbi.h-da.de/danet/gosdn/controller/topology/ports"
 	"code.fbi.h-da.de/danet/gosdn/controller/topology/store"
 )
 
@@ -16,19 +18,47 @@ type Service interface {
 
 // service is a service for ports
 type service struct {
-	store Store
+	store       Store
+	nodeService nodes.Service
+	portService ports.Service
 }
 
 // NewTopologyService creates a new TopologyService
-func NewTopologyService(store Store) Service {
+func NewTopologyService(
+	store Store,
+	nodeService nodes.Service,
+	portService ports.Service,
+) Service {
 	return &service{
-		store: store,
+		store:       store,
+		nodeService: nodeService,
+		portService: portService,
 	}
 }
 
 // AddLink adds a new link to the topology
 func (t *service) AddLink(link links.Link) error {
-	err := t.store.Add(link)
+	// These checks are also happening in the current NBI implementation.
+	// This should be refactored to only to these checks here.
+	_, err := t.nodeService.EnsureExists(link.SourceNode)
+	if err != nil {
+		return err
+	}
+	_, err = t.portService.EnsureExists(link.SourcePort)
+	if err != nil {
+		return err
+	}
+
+	_, err = t.nodeService.EnsureExists(link.TargetNode)
+	if err != nil {
+		return err
+	}
+	_, err = t.portService.EnsureExists(link.TargetPort)
+	if err != nil {
+		return err
+	}
+
+	err = t.store.Add(link)
 	if err != nil {
 		return err
 	}