{{- /*
Usage:

{{< blogPhoto "filename_relative_to_page.ext" "Alt text" >}}

or

{{< blogPhoto src="filename_relative_to_page.ext" alt="Alt text" … >}}

where possible named params are:
* src - path to the image in page bundle
* alt - textual description of the image, the <img> alt attribute
* caption (optional) - the caption displayed under the image, defaults to `alt`. Set to false to disable caption rendering

*/ -}}
{{- $imageName := false -}}
{{- $alt := false -}}
{{- if .IsNamedParams -}}
    {{- $imageName = .Get "src" | default nil -}}
    {{- $alt = .Get "alt" | default nil -}}
{{- else -}}
    {{- $imageName = .Get 0 -}}
    {{- $alt = .Get 1 -}}
{{- end -}}
{{- if (eq $imageName nil) }}{{ errorf "Missing image name in %s" .Position }}{{ end -}}
{{- if (eq $alt nil) }}{{ errorf "Missing alt for image %s in %s" $imageName .Position }}{{ end -}}
{{- $caption := cond (eq (.Get "caption") false) false (default $alt (.Get "caption")) -}}

{{- $img := .Page.Resources.GetMatch $imageName | default nil -}}
{{- if (eq $img nil) }}{{ errorf "Image %s not found in %s" $imageName .Position }}{{ end -}}
{{- $sizes := slice (slice 640 360 50) (slice 1280 720 50) (slice 1920 1080 50) -}}
{{- $srcset := slice -}}
{{- $largest := false -}}
{{- range $sizes -}}
    {{- if (or (gt $img.Width (index . 0)) (gt $img.Height (index . 1))) -}}
        {{- $resized := $img.Fit (printf "%dx%d q%d" (index . 0) (index . 1) (index . 2)) -}}
        {{- $srcset = $srcset | append (printf "%s %dw" $resized.RelPermalink (index . 0)) -}}
        {{- $largest = $resized -}}
    {{- end -}}
{{- end -}}

{{- if (lt (len $srcset) (len $sizes)) -}}
    {{- $compressed := $img.Fit (printf "%dx%d q90" $img.Width $img.Height) -}}
    {{- $srcset = $srcset | append (printf "%s %dw" $compressed.RelPermalink $compressed.Width) -}}
    {{- $largest = $compressed -}}
{{- end -}}

<figure>
    <a href="{{ $img.RelPermalink }}"><img src="{{ $largest.RelPermalink }}" alt="{{ $alt }}" srcset="{{ delimit $srcset ", " }}"></a>
    {{ if (ne $caption false) }}<figcaption>{{ $caption }}</figcaption>{{ end }}
</figure>
