Update

lib/nulla_web/controllers/activitypub/note_json.ex

@@ -0,0 +1,50 @@
+defmodule NullaWeb.ActivityPub.NoteJSON do
+  alias Nulla.Notes.Note
+
+  @doc """
+  Renders a single note.
+  """
+  def show(note) do
+    data(note)
+  end
+
+  defp data(%Note{} = note) do
+    attachment =
+      case note.media_attachments do
+        [] ->
+          []
+
+        attachments ->
+          [
+            attachment:
+              Enum.map(attachments, fn att ->
+                Jason.OrderedObject.new(
+                  type: "Document",
+                  mediaType: att.mime_type,
+                  url: "https://#{note.actor.domain}/files/#{att.file}"
+                )
+              end)
+          ]
+      end
+
+    Jason.OrderedObject.new(
+      "@context": [
+        "https://www.w3.org/ns/activitystreams",
+        Jason.OrderedObject.new(sensitive: "as:sensitive")
+      ],
+      id: "#{note.actor.ap_id}/notes/#{note.id}",
+      type: "Note",
+      summary: nil,
+      inReplyTo: note.inReplyTo,
+      published: note.published,
+      url: note.url,
+      attributedTo: note.actor.ap_id,
+      to: note.to,
+      cc: note.cc,
+      sensitive: note.sensitive,
+      content: note.content,
+      contentMap: Jason.OrderedObject.new("#{note.language}": note.content),
+      attachment: attachment
+    )
+  end
+end