micro: rewrite options to support multiple building blocks

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

register/watcher.go

@@ -0,0 +1,56 @@
+package register
+
+import "time"
+
+// Watcher is an interface that returns updates
+// about services within the register.
+type Watcher interface {
+	// Next is a blocking call
+	Next() (*Result, error)
+	Stop()
+}
+
+// Result is returned by a call to Next on
+// the watcher. Actions can be create, update, delete
+type Result struct {
+	Action  string
+	Service *Service
+}
+
+// EventType defines register event type
+type EventType int
+
+const (
+	// Create is emitted when a new service is registered
+	Create EventType = iota
+	// Delete is emitted when an existing service is deregistered
+	Delete
+	// Update is emitted when an existing service is updated
+	Update
+)
+
+// String returns human readable event type
+func (t EventType) String() string {
+	switch t {
+	case Create:
+		return "create"
+	case Delete:
+		return "delete"
+	case Update:
+		return "update"
+	default:
+		return "unknown"
+	}
+}
+
+// Event is register event
+type Event struct {
+	// Id is register id
+	Id string
+	// Type defines type of event
+	Type EventType
+	// Timestamp is event timestamp
+	Timestamp time.Time
+	// Service is register service
+	Service *Service
+}