simplify some code and implement metrics storage

internal/watcher/health/status.go

@@ -1,5 +1,7 @@
 package health
 
+import "encoding/json"
+
 type Status uint8
 
 const (
@@ -37,6 +39,28 @@ func (s Status) MarshalJSON() ([]byte, error) {
 	return []byte(`"` + s.String() + `"`), nil
 }
 
+func (s *Status) UnmarshalJSON(data []byte) error {
+	var str string
+	if err := json.Unmarshal(data, &str); err != nil {
+		return err
+	}
+	switch str {
+	case "healthy":
+		*s = StatusHealthy
+	case "unhealthy":
+		*s = StatusUnhealthy
+	case "napping":
+		*s = StatusNapping
+	case "starting":
+		*s = StatusStarting
+	case "error":
+		*s = StatusError
+	default:
+		*s = StatusUnknown
+	}
+	return nil
+}
+
 func (s Status) Good() bool {
 	return s&HealthyMask != 0
 }