hugo amp lightbox image shortcode with unique ID assignment

img.html

<!-- you also need to add the following script
<script async custom-element="amp-image-lightbox" src="https://cdn.ampproject.org/v0/amp-image-lightbox-0.1.js"></script>
-->
{{$unique_id := now.UnixNano}}
<amp-image-lightbox id="{{ $unique_id }}"
  layout="nodisplay"></amp-image-lightbox>
<figure {{ if .Get "class" }} class='{{ .Get "class" }}'
{{else}} class="image-center" {{ end }} >
  <amp-img
    on='tap:{{ $unique_id }}'
    tabindex="0"
    role="button"
    src="{{ .Get "src" }}"
    alt="{{ .Page.Title }} {{ .Get "src" }}"
    width={{ .Get "w" | default "200" }}
    height={{ .Get "h" | default "200"}}>
  </amp-img>
  {{ if .Get "caption" }}
  <figcaption>
    {{ if .Get "href" }}
    <a href="{{ .Get "href" }}" target="_blank">{{ .Get "caption" }}</a>
    {{ else }}
    {{ .Get "caption" }}
    {{ end }}
  </figcaption>
  {{ end }}
</figure>