Implement GET /api/v1/announcements/:id

lib/pleroma/web/mastodon_api/controllers/announcement_controller.ex

@@ -55,7 +55,20 @@ defmodule Pleroma.Web.MastodonAPI.AnnouncementController do
   end
 
   @doc "POST /api/v1/announcements/:id"
-  def show(_conn, _params) do
-    {:error, :not_found}
+  def show(%{assigns: %{user: user}} = conn, %{id: id} = _params) do
+    render_announcement_by_id(conn, id, user)
+  end
+
+  def show(conn, %{id: id} = _params) do
+    render_announcement_by_id(conn, id)
+  end
+
+  def render_announcement_by_id(conn, id, user \\ nil) do
+    with announcement when not is_nil(announcement) <- Announcement.get_by_id(id) do
+      render(conn, "show.json", announcement: announcement, user: user)
+    else
+      _ ->
+        {:error, :not_found}
+    end
   end
 end