tpl/tplimpl: Improve embedded opengraph template

Changes:

- Add tags per documentation
- Prefer site.Title over site.Params.title
- Plainify titles, tags, and descriptions
- Add fallback values for locale
- Fix pages related by series
- Improve readability

Closes gohugoio#8296
Closes gohugoio#8698
Closes gohugoio#8991
Closes gohugoio#9818
Closes gohugoio#9866
Closes gohugoio#10647

Co-authored by: tomy0000000 <git@tomy.me>
Co-authored by: sean-au <sean@powerfulwebdesign.com.au>

tpl/tplimpl/embedded/templates/opengraph.html

@@ -1,44 +1,72 @@
-<meta property="og:title" content="{{ .Title }}">
-<meta property="og:description" content="{{ with .Description }}{{ . }}{{ else }}{{if .IsPage}}{{ .Summary }}{{ else }}{{ with .Site.Params.description }}{{ . }}{{ end }}{{ end }}{{ end }}">
-<meta property="og:type" content="{{ if .IsPage }}article{{ else }}website{{ end }}">
 <meta property="og:url" content="{{ .Permalink }}">
 
-{{- $images := partial "_funcs/get-page-images" . -}}
-{{- range first 6 $images -}}
-  <meta property="og:image" content="{{ .Permalink }}">
-{{- end -}}
+{{- with or site.Title site.Params.title | plainify }}
+  <meta property="og:site_name" content="{{ . }}">
+{{- end }}
+
+{{- with or .Title site.Title site.Params.title | plainify}}
+  <meta property="og:title" content="{{ . }}">
+{{- end }}
+
+{{- with or .Description .Summary site.Params.description | plainify }}
+  <meta property="og:description" content="{{ . }}">
+{{- end }}
+
+{{- with or .Params.locale site.Language.LanguageCode site.Language.Lang }}
+  <meta property="og:locale" content="{{ . }}">
+{{- end }}
 
 {{- if .IsPage }}
-{{- $iso8601 := "2006-01-02T15:04:05-07:00" -}}
-<meta property="article:section" content="{{ .Section }}">
-{{ with .PublishDate }}<meta property="article:published_time" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }}>{{ end }}
-{{ with .Lastmod }}<meta property="article:modified_time" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }}>{{ end }}
-{{- end -}}
-
-{{- with .Params.audio }}<meta property="og:audio" content="{{ . }}">{{ end }}
-{{- with .Params.locale }}<meta property="og:locale" content="{{ . }}">{{ end }}
-{{- with .Site.Params.title }}<meta property="og:site_name" content="{{ . }}">{{ end }}
-{{- with .Params.videos }}{{- range . }}
-<meta property="og:video" content="{{ . | absURL }}">
-{{ end }}{{ end }}
-
-{{- /* If it is part of a series, link to related articles */}}
-{{- $permalink := .Permalink }}
-{{- $siteSeries := .Site.Taxonomies.series }}
-{{- if $siteSeries }}
-{{ with .Params.series }}{{- range $name := . }}
-  {{- $series := index $siteSeries ($name | urlize) }}
-  {{- range $page := first 6 $series.Pages }}
-    {{- if ne $page.Permalink $permalink }}<meta property="og:see_also" content="{{ $page.Permalink }}">{{ end }}
-  {{- end }}
-{{ end }}{{ end }}
-{{- end }}
-
-{{- /* Facebook Page Admin ID for Domain Insights */}}
+  <meta property="og:type" content="article">
+  <meta property="article:section" content="{{ .Section }}">
+  {{- $ISO8601 := "2006-01-02T15:04:05-07:00" }}
+  {{- with .PublishDate }}
+    <meta property="article:published_time" {{ .Format $ISO8601 | printf "content=%q" | safeHTMLAttr }}>
+  {{- end }}
+  {{- with .Lastmod }}
+    <meta property="article:modified_time" {{ .Format $ISO8601 | printf "content=%q" | safeHTMLAttr }}>
+  {{- end }}
+  {{- range .GetTerms "tags" | first 6 }}
+    <meta property="article:tag" content="{{ .Page.Title | plainify }}">
+  {{- end }}
+{{- else }}
+  <meta property="og:type" content="website">
+{{- end }}
+
+{{- with partial "_funcs/get-page-images" . }}
+  {{- range . | first 6 }}
+    <meta property="og:image" content="{{ .Permalink }}">
+  {{- end }}
+{{- end }}
+
+{{- with .Params.audio }}
+  {{- range . | first 6  }}
+    <meta property="og:audio" content="{{ . | absURL }}">
+  {{- end }}
+{{- end }}
+
+{{- with .Params.videos }}
+  {{- range . | first 6 }}
+    <meta property="og:video" content="{{ . | absURL }}">
+  {{- end }}
+{{- end }}
+
+{{- range .GetTerms "series" }}
+  {{- range .Pages | first 7 }}
+    {{- if not ($.Eq .) }}
+      <meta property="og:see_also" content="{{ .Permalink }}">
+    {{- end }}
+  {{- end }}
+{{- end }}
+
 {{- with site.Params.social }}
   {{- if reflect.IsMap . }}
-    {{- with .facebook_admin }}
-      <meta property="fb:admins" content="{{ . }}">
+    {{- with .facebook_app_id }}
+      <meta property="fb:app_id" content="{{ . }}">
+    {{- else }}
+      {{- with .facebook_admin }}
+        <meta property="fb:admins" content="{{ . }}">
+      {{- end }}
     {{- end }}
   {{- end }}
 {{- end }}