Use OrderedCollectionPage to return followers/following list (#4949)

app/controllers/follower_accounts_controller.rb

@@ -17,12 +17,29 @@ class FollowerAccountsController < ApplicationController
 
   private
 
+  def page_url(page)
+    account_followers_url(@account, page: page) unless page.nil?
+  end
+
   def collection_presenter
+    page = ActivityPub::CollectionPresenter.new(
+      id: account_followers_url(@account, page: params.fetch(:page, 1)),
+      type: :ordered,
+      size: @account.followers_count,
+      items: @follows.map { |f| ActivityPub::TagManager.instance.uri_for(f.account) },
+      part_of: account_followers_url(@account),
+      next: page_url(@follows.next_page),
+      prev: page_url(@follows.prev_page)
+    )
+    if params[:page].present?
+      page
+    else
       ActivityPub::CollectionPresenter.new(
         id: account_followers_url(@account),
         type: :ordered,
         size: @account.followers_count,
-      items: @follows.map { |f| ActivityPub::TagManager.instance.uri_for(f.account) }
+        first: page
       )
     end
+  end
 end

app/controllers/following_accounts_controller.rb

@@ -17,12 +17,29 @@ class FollowingAccountsController < ApplicationController
 
   private
 
+  def page_url(page)
+    account_following_index_url(@account, page: page) unless page.nil?
+  end
+
   def collection_presenter
+    page = ActivityPub::CollectionPresenter.new(
+      id: account_following_index_url(@account, page: params.fetch(:page, 1)),
+      type: :ordered,
+      size: @account.following_count,
+      items: @follows.map { |f| ActivityPub::TagManager.instance.uri_for(f.target_account) },
+      part_of: account_following_index_url(@account),
+      next: page_url(@follows.next_page),
+      prev: page_url(@follows.prev_page)
+    )
+    if params[:page].present?
+      page
+    else
       ActivityPub::CollectionPresenter.new(
         id: account_following_index_url(@account),
         type: :ordered,
         size: @account.following_count,
-      items: @follows.map { |f| ActivityPub::TagManager.instance.uri_for(f.target_account) }
+        first: page
       )
     end
+  end
 end

app/presenters/activitypub/collection_presenter.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 class ActivityPub::CollectionPresenter < ActiveModelSerializers::Model
-  attributes :id, :type, :size, :items
+  attributes :id, :type, :size, :items, :part_of, :first, :next, :prev
 end

app/serializers/activitypub/collection_serializer.rb

@@ -3,23 +3,38 @@
 class ActivityPub::CollectionSerializer < ActiveModel::Serializer
   def self.serializer_for(model, options)
     return ActivityPub::ActivitySerializer if model.class.name == 'Status'
+    return ActivityPub::CollectionSerializer if model.class.name == 'ActivityPub::CollectionPresenter'
     super
   end
 
   attributes :id, :type, :total_items
+  attribute :next, if: -> { object.next.present? }
+  attribute :prev, if: -> { object.prev.present? }
+  attribute :part_of, if: -> { object.part_of.present? }
 
-  has_many :items, key: :ordered_items
+  has_one :first, if: -> { object.first.present? }
+  has_many :items, key: :items, if: -> { (object.items.present? || page?) && !ordered? }
+  has_many :items, key: :ordered_items, if: -> { (object.items.present? || page?) && ordered? }
 
   def type
-    case object.type
+    if page?
-    when :ordered
+      ordered? ? 'OrderedCollectionPage' : 'CollectionPage'
-      'OrderedCollection'
     else
-      'Collection'
+      ordered? ? 'OrderedCollection' : 'Collection'
     end
   end
 
   def total_items
     object.size
   end
+
+  private
+
+  def ordered?
+    object.type == :ordered
+  end
+
+  def page?
+    object.part_of.present?
+  end
 end