tpl: Allow using page resources on the images page parameter for opengraph, schema and twitter_cards templates

The page images selection order as follows:

1. Page's images parameter, image resources are supported.
2. Page's image resources that naming in *feature*, *cover* or *thumbnail* pattern.
3. If no page images specified, then the first one of site's images will be used as the fallback, supports site resources.

tpl/tplimpl/embedded/templates/opengraph.html

@@ -3,17 +3,9 @@
 <meta property="og:type" content="{{ if .IsPage }}article{{ else }}website{{ end }}" />
 <meta property="og:url" content="{{ .Permalink }}" />
 
-{{- with $.Params.images -}}
-{{- range first 6 . }}<meta property="og:image" content="{{ . | absURL }}" />{{ end -}}
-{{- else -}}
-{{- $images := $.Resources.ByType "image" -}}
-{{- $featured := $images.GetMatch "*feature*" -}}
-{{- if not $featured }}{{ $featured = $images.GetMatch "{*cover*,*thumbnail*}" }}{{ end -}}
-{{- with $featured -}}
-<meta property="og:image" content="{{ $featured.Permalink }}"/>
-{{- else -}}
-{{- with $.Site.Params.images }}<meta property="og:image" content="{{ index . 0 | absURL }}"/>{{ end -}}
-{{- end -}}
+{{- $images := partial "_funcs/get-page-images" . -}}
+{{- range first 6 $images -}}
+  <meta property="og:image" content="{{ .Permalink }}" />
 {{- end -}}
 
 {{- if .IsPage }}

tpl/tplimpl/embedded/templates/partials/_funcs/get-page-images.html

@@ -0,0 +1,47 @@
+{{- $imgs := slice }}
+{{- $imgParams := .Params.images }}
+{{- $resources := .Resources.ByType "image" -}}
+{{/* Find featured image resources if the images parameter is empty. */}}
+{{- if not $imgParams }}
+  {{- $featured := $resources.GetMatch "*feature*" -}}
+  {{- if not $featured }}{{ $featured = $resources.GetMatch "{*cover*,*thumbnail*}" }}{{ end -}}
+  {{- with $featured }}
+    {{- $imgs = $imgs | append (dict
+      "Image" .
+      "RelPermalink" .RelPermalink
+      "Permalink" .Permalink) }}
+  {{- end }}
+{{- end }}
+{{/* Use the first one of site images as the fallback. */}}
+{{- if and (not $imgParams) (not $imgs) }}
+  {{- with site.Params.images }}
+    {{- $imgParams = first 1 . }}
+  {{- end }}
+{{- end }}
+{{/* Parse page's images parameter. */}}
+{{- range $imgParams }}
+  {{- $img := . }}
+  {{- $url := urls.Parse $img }}
+  {{- if eq $url.Scheme "" }}
+    {{/* Internal image. */}}
+    {{- with $resources.GetMatch $img -}}
+      {{/* Image resource. */}}
+      {{- $imgs = $imgs | append (dict
+        "Image" .
+        "RelPermalink" .RelPermalink
+        "Permalink" .Permalink) }}
+    {{- else }}
+      {{- $imgs = $imgs | append (dict
+        "RelPermalink" (relURL $img)
+        "Permalink" (absURL $img)
+      ) }}
+    {{- end }}
+  {{- else }}
+    {{/* External image */}}
+    {{- $imgs = $imgs | append (dict
+      "RelPermalink" $img
+      "Permalink" $img
+    ) }}
+  {{- end }}
+{{- end }}
+{{- return $imgs }}

tpl/tplimpl/embedded/templates/schema.html

@@ -7,17 +7,9 @@
 {{ with .Lastmod }}<meta itemprop="dateModified" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end}}
 <meta itemprop="wordCount" content="{{ .WordCount }}">
 
-{{- with $.Params.images -}}
-{{- range first 6 . -}}<meta itemprop="image" content="{{ . | absURL }}">{{ end -}}
-{{- else -}}
-{{- $images := $.Resources.ByType "image" -}}
-{{- $featured := $images.GetMatch "*feature*" -}}
-{{- if not $featured }}{{ $featured = $images.GetMatch "{*cover*,*thumbnail*}" }}{{ end -}}
-{{- with $featured -}}
-<meta itemprop="image" content="{{ $featured.Permalink }}">
-{{- else -}}
-{{- with $.Site.Params.images -}}<meta itemprop="image" content="{{ index . 0 | absURL }}"/>{{ end -}}
-{{- end -}}
+{{- $images := partial "_funcs/get-page-images" . -}}
+{{- range first 6 $images -}}
+  <meta itemprop="image" content="{{ .Permalink }}" />
 {{- end -}}
 
 <!-- Output all taxonomies as schema.org keywords -->

tpl/tplimpl/embedded/templates/twitter_cards.html

@@ -1,22 +1,10 @@
-{{- with $.Params.images -}}
-<meta name="twitter:card" content="summary_large_image"/>
-<meta name="twitter:image" content="{{ index . 0 | absURL }}"/>
-{{ else -}}
-{{- $images := $.Resources.ByType "image" -}}
-{{- $featured := $images.GetMatch "*feature*" -}}
-{{- if not $featured }}{{ $featured = $images.GetMatch "{*cover*,*thumbnail*}" }}{{ end -}}
-{{- with $featured -}}
-<meta name="twitter:card" content="summary_large_image"/>
-<meta name="twitter:image" content="{{ $featured.Permalink }}"/>
+{{- $images := partial "_funcs/get-page-images" . -}}
+{{- with index $images 0 -}}
+<meta name="twitter:card" content="summary_large_image" />
+<meta name="twitter:image" content="{{ .Permalink }}" />
 {{- else -}}
-{{- with $.Site.Params.images -}}
-<meta name="twitter:card" content="summary_large_image"/>
-<meta name="twitter:image" content="{{ index . 0 | absURL }}"/>
-{{ else -}}
 <meta name="twitter:card" content="summary"/>
 {{- end -}}
-{{- end -}}
-{{- end }}
 <meta name="twitter:title" content="{{ .Title }}"/>
 <meta name="twitter:description" content="{{ with .Description }}{{ . }}{{ else }}{{if .IsPage}}{{ .Summary }}{{ else }}{{ with .Site.Params.description }}{{ . }}{{ end }}{{ end }}{{ end -}}"/>