From 7c03d2627f7da617282c9eade17dc22e537d6643 Mon Sep 17 00:00:00 2001
From: Shadowfacts <me@shadowfacts.net>
Date: Wed, 2 Oct 2019 11:12:34 -0400
Subject: [PATCH] Add AP followers endpoint

---
 lib/clacks/actor.ex                           |  4 +-
 .../controllers/actor_controller.ex           | 76 +++++++++++++++++--
 .../controllers/web_finger_controller.ex      |  2 +-
 lib/clacks_web/router.ex                      |  2 +
 4 files changed, 75 insertions(+), 9 deletions(-)

diff --git a/lib/clacks/actor.ex b/lib/clacks/actor.ex
index 897d4da..4e772a9 100644
--- a/lib/clacks/actor.ex
+++ b/lib/clacks/actor.ex
@@ -27,8 +27,8 @@ defmodule Clacks.Actor do
     |> validate_required([:ap_id, :nickname, :local, :data])
   end
 
-  @spec get_by_nickanme(nickname :: String.t()) :: t() | nil
-  def get_by_nickanme(nickname) do
+  @spec get_by_nickname(nickname :: String.t()) :: t() | nil
+  def get_by_nickname(nickname) do
     Repo.one(from a in __MODULE__, where: a.nickname == ^nickname)
   end
 
diff --git a/lib/clacks_web/controllers/actor_controller.ex b/lib/clacks_web/controllers/actor_controller.ex
index c9cca06..b0a47fd 100644
--- a/lib/clacks_web/controllers/actor_controller.ex
+++ b/lib/clacks_web/controllers/actor_controller.ex
@@ -1,10 +1,28 @@
 defmodule ClacksWeb.ActorController do
   use ClacksWeb, :controller
-  alias Clacks.{Repo, Actor}
+  alias Clacks.Actor
   import Ecto.Query
 
-  def get(conn, %{"nickname" => nickname}) do
-    case Actor.get_by_nickanme(nickname) do
+  @context "https://www.w3.org/ns/activitystreams"
+
+  plug :get_actor
+
+  defp get_actor(%Plug.Conn{path_params: %{"nickname" => nickname}} = conn, _opts) do
+    case Actor.get_by_nickname(nickname) do
+      nil ->
+        conn
+        |> put_status(404)
+        |> halt()
+
+      actor ->
+        assign(conn, :actor, actor)
+    end
+  end
+
+  defp get_actor(conn, _opts), do: conn
+
+  def get(conn, _params) do
+    case conn.assigns[:actor] do
       %Actor{local: true, data: data} ->
         conn
         |> put_resp_header("content-type", "application/activity+json")
@@ -13,10 +31,56 @@ defmodule ClacksWeb.ActorController do
       %Actor{local: false, ap_id: ap_id} ->
         conn
         |> redirect(external: ap_id)
+    end
+  end
 
-      _ ->
-        conn
-        |> put_status(404)
+  def followers(conn, %{"page" => page}) do
+    {page, _} = Integer.parse(page)
+
+    followers = conn.assigns[:actor].followers
+
+    data =
+      collection_page(conn, followers, page)
+      |> Map.put("@context", @context)
+
+    conn
+    |> put_resp_header("content-type", "application/activity+json")
+    |> json(data)
+  end
+
+  def followers(conn, _params) do
+    %Actor{followers: followers} = conn.assigns[:actor]
+
+    data = %{
+      "@context" => @context,
+      "type" => "OrderedCollection",
+      "id" => current_url(conn, %{}),
+      "totalItems" => length(followers),
+      "first" => collection_page(conn, followers, 1)
+    }
+
+    conn
+    |> put_resp_header("content-type", "application/activity+json")
+    |> json(data)
+  end
+
+  defp collection_page(conn, collection, page) do
+    chunks = Enum.chunk_every(collection, 20)
+    # page is 1 indexed, so subtract 1 to get the current chunk
+    current_chunk = Enum.at(chunks, page - 1)
+
+    data = %{
+      "type" => "OrderedCollectionPage",
+      "totalItems" => length(collection),
+      "partOf" => current_url(conn, %{}),
+      "id" => current_url(conn, %{page: page}),
+      "orderedItems" => current_chunk || []
+    }
+
+    if page < length(chunks) do
+      Map.put(data, "next", current_url(conn, %{page: page + 1}))
+    else
+      data
     end
   end
 end
diff --git a/lib/clacks_web/controllers/web_finger_controller.ex b/lib/clacks_web/controllers/web_finger_controller.ex
index ebd817a..a284b21 100644
--- a/lib/clacks_web/controllers/web_finger_controller.ex
+++ b/lib/clacks_web/controllers/web_finger_controller.ex
@@ -6,7 +6,7 @@ defmodule ClacksWeb.WebFingerController do
 
   def get(conn, %{"resource" => resource}) do
     with [_, nickname] <- Regex.run(@acct_regex, resource),
-         %Actor{local: true} = actor <- Actor.get_by_nickanme(nickname) do
+         %Actor{local: true} = actor <- Actor.get_by_nickname(nickname) do
       url = Application.get_env(:clacks, ClacksWeb.Endpoint)[:url]
       host = url[:host]
       port = url[:port]
diff --git a/lib/clacks_web/router.ex b/lib/clacks_web/router.ex
index f45547d..55c9724 100644
--- a/lib/clacks_web/router.ex
+++ b/lib/clacks_web/router.ex
@@ -21,7 +21,9 @@ defmodule ClacksWeb.Router do
     pipe_through :activitypub
 
     get "/objects/:id", ObjectsController, :get
+
     get "/users/:nickname", ActorController, :get
+    get "/users/:nickname/followers", ActorController, :followers
 
     post "/inbox", InboxController, :shared
     post "/users/:nickname/inbox", InboxController, :user_specific