Extract RSS Feed functionality from OStatus

lib/pleroma/web/feed/feed_controller.ex

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+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.Feed.FeedController do
+  use Pleroma.Web, :controller
+
+  alias Fallback.RedirectController
+  alias Pleroma.User
+  alias Pleroma.Web.ActivityPub.ActivityPub
+  alias Pleroma.Web.ActivityPub.ActivityPubController
+
+  plug(Pleroma.Plugs.SetFormatPlug when action in [:feed_redirect])
+
+  action_fallback(:errors)
+
+  def feed_redirect(%{assigns: %{format: "html"}} = conn, %{"nickname" => nickname}) do
+    with {_, %User{} = user} <- {:fetch_user, User.get_cached_by_nickname_or_id(nickname)} do
+      RedirectController.redirector_with_meta(conn, %{user: user})
+    end
+  end
+
+  def feed_redirect(%{assigns: %{format: format}} = conn, _params)
+      when format in ["json", "activity+json"] do
+    ActivityPubController.call(conn, :user)
+  end
+
+  def feed_redirect(conn, %{"nickname" => nickname}) do
+    with {_, %User{} = user} <- {:fetch_user, User.get_cached_by_nickname(nickname)} do
+      redirect(conn, external: "#{feed_url(conn, :feed, user.nickname)}.atom")
+    end
+  end
+
+  def feed(conn, %{"nickname" => nickname} = params) do
+    with {_, %User{} = user} <- {:fetch_user, User.get_cached_by_nickname(nickname)} do
+      query_params =
+        params
+        |> Map.take(["max_id"])
+        |> Map.put("type", ["Create"])
+        |> Map.put("whole_db", true)
+        |> Map.put("actor_id", user.ap_id)
+
+      activities =
+        query_params
+        |> ActivityPub.fetch_public_activities()
+        |> Enum.reverse()
+
+      conn
+      |> put_resp_content_type("application/atom+xml")
+      |> render("feed.xml", user: user, activities: activities)
+    end
+  end
+
+  def errors(conn, {:error, :not_found}) do
+    render_error(conn, :not_found, "Not found")
+  end
+
+  def errors(conn, {:fetch_user, nil}), do: errors(conn, {:error, :not_found})
+
+  def errors(conn, _) do
+    render_error(conn, :internal_server_error, "Something went wrong")
+  end
+end