Helm templating.. values match

Question

Wondering whether it's possible to use a port if it exists in the values, else use http.. something like this;

svc:
  app:
    ports:
      - port: 8080
        name: http
      - port: 8090
        name: metrics
  app2:
    ports:
      - port: 8080
        name: http

Some service expose their metrics over http and some have metrics ports.. So I'd like to template it something like;

{{ define "app.service.ports" }}
{{ range (index .Values.svc (include "app.refName" .) "ports") }}
- name: {{ .name }}
{{ end }}
{{ end }}

This will pull each port name right, but I want to pull metrics if it exists, else pull http.. can someone point me in the right direction?