ap/views: factor out common keyset collection bits

The enxt commit will add another user of the new function.

lib/pleroma/web/activity_pub/activity_pub_controller.ex

@@ -287,8 +287,7 @@ def outbox(
       |> put_view(UserView)
       |> render("activity_collection_page.json", %{
         activities: activities,
-        pagination: ControllerHelper.get_pagination_fields(conn, activities),
-        iri: "#{user.ap_id}/outbox"
+        pagination: ControllerHelper.get_pagination_fields(conn, activities)
       })
     end
   end
@@ -368,8 +367,7 @@ def read_inbox(
     |> put_view(UserView)
     |> render("activity_collection_page.json", %{
       activities: activities,
-      pagination: ControllerHelper.get_pagination_fields(conn, activities),
-      iri: "#{user.ap_id}/inbox"
+      pagination: ControllerHelper.get_pagination_fields(conn, activities)
     })
   end
 

lib/pleroma/web/activity_pub/views/collection_view_helper.ex

@@ -4,7 +4,7 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule Pleroma.Web.ActivityPub.CollectionViewHelper do
-  alias Pleroma.Web.ControllerHelper
+  alias Pleroma.Web.ActivityPub.Utils
 
   def collection_page_offset(collection, iri, page, show_items \\ true, total \\ nil) do
     offset = (page - 1) * 10
@@ -26,4 +26,27 @@ def collection_page_offset(collection, iri, page, show_items \\ true, total \\ n
       map
     end
   end
+
+  defp maybe_omit_next(pagination, _items, nil), do: pagination
+
+  defp maybe_omit_next(pagination, items, limit) do
+    if Enum.count(items) < limit, do: Map.delete(pagination, "next"), else: pagination
+  end
+
+  def collection_page_keyset(
+        display_items,
+        pagination,
+        limit \\ nil,
+        skip_ap_context \\ false
+      ) do
+    %{
+      "type" => "OrderedCollectionPage",
+      "orderedItems" => display_items
+    }
+    |> Map.merge(pagination)
+    |> maybe_omit_next(display_items, limit)
+    |> then(fn m ->
+      if skip_ap_context, do: m, else: Map.merge(m, Utils.make_json_ld_header())
+    end)
+  end
 end

lib/pleroma/web/activity_pub/views/user_view.ex

@@ -8,6 +8,7 @@ defmodule Pleroma.Web.ActivityPub.UserView do
   alias Pleroma.Object
   alias Pleroma.Repo
   alias Pleroma.User
+  alias Pleroma.Web.ActivityPub.CollectionViewHelper
   alias Pleroma.Web.ActivityPub.ObjectView
   alias Pleroma.Web.ActivityPub.Transmogrifier
   alias Pleroma.Web.ActivityPub.Utils
@@ -256,22 +257,15 @@ def render("activity_collection.json", %{iri: iri}) do
 
   def render("activity_collection_page.json", %{
         activities: activities,
-        iri: iri,
         pagination: pagination
       }) do
-    collection =
+    display_items =
       Enum.map(activities, fn activity ->
         {:ok, data} = Transmogrifier.prepare_outgoing(activity.data)
         data
       end)
 
-    %{
-      "type" => "OrderedCollectionPage",
-      "partOf" => iri,
-      "orderedItems" => collection
-    }
-    |> Map.merge(Utils.make_json_ld_header())
-    |> Map.merge(pagination)
+    CollectionViewHelper.collection_page_keyset(display_items, pagination)
   end
 
   def render("featured.json", %{

lib/pleroma/web/controller_helper.ex

@@ -66,10 +66,14 @@ defp build_pagination_fields(conn, min_id, max_id, extra_params, order) do
         do: {{:max_id, max_id}, {:min_id, min_id}},
         else: {{:min_id, min_id}, {:max_id, max_id}}
 
+    id = Phoenix.Controller.current_url(conn)
+    base_id = %{URI.parse(id) | query: nil} |> URI.to_string()
+
     %{
       "next" => current_url(conn, Map.put(params, next_id, nid)),
       "prev" => current_url(conn, Map.put(params, prev_id, pid)),
-      "id" => current_url(conn)
+      "id" => id,
+      "partOf" => base_id
     }
   end