Fix display names/usernames being switched

lib/clacks_web/templates/frontend/_status.html.eex

@@ -3,7 +3,7 @@
     <div class="p-author h-card">
       <h2 class="status-author-nickname">
         <a href="<%= local_actor_link(@author) %>">
-          <%= @author.data["preferredUsername"] %>
+          <%= display_name(@author) %>
         </a>
       </h2>
       <h3 class="status-author-username">

lib/clacks_web/views/frontend_view.ex

@@ -7,13 +7,27 @@ defmodule ClacksWeb.FrontendView do
 
   @spec display_username(actor :: Actor.t()) :: String.t()
 
-  def display_username(%Actor{local: true, data: %{"name" => name}}) do
-    "@" <> name
+  def display_username(%Actor{local: true, data: %{"preferredUsername" => username}}) do
+    "@" <> username
   end
 
-  def display_username(%Actor{local: false, ap_id: ap_id, data: %{"name" => name}}) do
+  def display_username(%Actor{
+        local: false,
+        ap_id: ap_id,
+        data: %{"preferredUsername" => username}
+      }) do
     %URI{host: host} = URI.parse(ap_id)
-    "@" <> name <> "@" <> host
+    "@" <> username <> "@" <> host
+  end
+
+  @spec display_name(actor :: Actor.t()) :: String.t()
+
+  def display_name(%Actor{data: %{"name" => name, "preferredUsername" => username}}) do
+    if is_binary(name) && String.length(name) > 0 do
+      name
+    else
+      username
+    end
   end
 
   def local_actor_link(%Actor{local: true, ap_id: ap_id}), do: ap_id