Introduce group posts

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/service/metadata/post.ex

@@ -0,0 +1,34 @@
+defimpl Mobilizon.Service.Metadata, for: Mobilizon.Posts.Post do
+  alias Phoenix.HTML
+  alias Phoenix.HTML.Tag
+  alias Mobilizon.Posts.Post
+  alias Mobilizon.Web.JsonLD.ObjectView
+  import Mobilizon.Service.Metadata.Utils, only: [process_description: 2, strip_tags: 1]
+
+  def build_tags(%Post{} = post, locale \\ "en") do
+    post = Map.put(post, :body, process_description(post.body, locale))
+
+    tags = [
+      Tag.tag(:meta, property: "og:title", content: post.title),
+      Tag.tag(:meta, property: "og:url", content: post.url),
+      Tag.tag(:meta, property: "og:description", content: post.body),
+      Tag.tag(:meta, property: "og:type", content: "article"),
+      Tag.tag(:meta, property: "twitter:card", content: "summary"),
+      # Tell Search Engines what's the origin
+      Tag.tag(:link, rel: "canonical", href: post.url)
+    ]
+
+    tags ++
+      [
+        Tag.tag(:meta, property: "twitter:card", content: "summary_large_image"),
+        ~s{<script type="application/ld+json">#{json(post)}</script>} |> HTML.raw()
+      ]
+  end
+
+  # Insert JSON-LD schema by hand because Tag.content_tag wants to escape it
+  defp json(%Post{title: title} = post) do
+    "post.json"
+    |> ObjectView.render(%{post: %{post | title: strip_tags(title)}})
+    |> Jason.encode!()
+  end
+end