{{/* get file that matches the filename as specified as src="" in shortcode */}}
{{ $src := .Page.Resources.GetMatch (printf "*%s*" (.Get "src")) }}

{{/* set image sizes, these are hardcoded for now, x dictates that images are resized to this width */}}

{{ $tinyw := default "500x" }}
{{ $smallw := default "800x" }}
{{ $mediumw := default "1200x" }}
{{ $largew := default "1500x" }}

{{/* resize the src image to the given sizes */}}

{{ .Scratch.Set "tiny" ($src.Resize $tinyw) }}
{{ .Scratch.Set "small" ($src.Resize $smallw) }}
{{ .Scratch.Set "medium" ($src.Resize $mediumw) }}
{{ .Scratch.Set "large" ($src.Resize $largew) }}

{{/* add the processed images to the scratch */}}

{{ $tiny := .Scratch.Get "tiny" }}
{{ $small := .Scratch.Get "small" }}
{{ $medium := .Scratch.Get "medium" }}
{{ $large := .Scratch.Get "large" }}

{{/* only use images smaller than or equal to the src (original) image size, as Hugo will upscale small images */}}
{{/* set the sizes attribute to (min-width: 35em) 1200px, 100vw unless overridden in shortcode */}}

<img 
  {{ with .Get "sizes" }}sizes='{{.}}'{{ else }}sizes="(min-width: 35em) 1200px, 100vw"{{ end }}
  srcset='
  {{ if ge $src.Width "500" }}
    {{ with $tiny.RelPermalink }}{{.}} 500w{{ end }}
  {{ end }}
  {{ if ge $src.Width "800" }}
    {{ with $small.RelPermalink }}, {{.}} 800w{{ end }}
  {{ end }}
  {{ if ge $src.Width "1200" }}
    {{ with $medium.RelPermalink }}, {{.}} 1200w{{ end }}
  {{ end }}
  {{ if ge $src.Width "1500" }}
    {{ with $large.RelPermalink }}, {{.}} 1500w {{ end }}
  {{ end }}'
  {{ if .Get (print $medium) }}
    src="{{ $medium.RelPermalink }}" 
  {{ else }}
    src="{{ $src.RelPermalink }}" 
  {{ end }}
  {{ with .Get "alt" }}alt="{{.}}"{{ else }}alt=""{{ end }}>