1 files changed, 71 insertions, 0 deletions
diff --git a/app/controllers/activitypub/replies_controller.rb b/app/controllers/activitypub/replies_controller.rb
new file mode 100644
index 000000000..c62061555
--- /dev/null
+++ b/app/controllers/activitypub/replies_controller.rb
@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+class ActivityPub::RepliesController < ActivityPub::BaseController
+  include SignatureAuthentication
+  include Authorization
+  include AccountOwnedConcern
+
+  DESCENDANTS_LIMIT = 60
+
+  before_action :require_signature!, if: :authorized_fetch_mode?
+  before_action :set_status
+  before_action :set_cache_headers
+  before_action :set_replies
+
+  def index
+    expires_in 0, public: public_fetch_mode?
+    render json: replies_collection_presenter, serializer: ActivityPub::CollectionSerializer, adapter: ActivityPub::Adapter, content_type: 'application/activity+json', skip_activities: true
+  end
+
+  private
+
+  def set_status
+    @status = @account.statuses.find(params[:status_id])
+    authorize @status, :show?
+  rescue Mastodon::NotPermittedError
+    raise ActiveRecord::RecordNotFound
+  end
+
+  def set_replies
+    @replies = page_params[:only_other_accounts] ? Status.where.not(account_id: @account.id) : @account.statuses
+    @replies = @replies.where(in_reply_to_id: @status.id, visibility: [:public, :unlisted])
+    @replies = @replies.paginate_by_min_id(DESCENDANTS_LIMIT, params[:min_id])
+  end
+
+  def replies_collection_presenter
+    page = ActivityPub::CollectionPresenter.new(
+      id: account_status_replies_url(@account, @status, page_params),
+      type: :unordered,
+      part_of: account_status_replies_url(@account, @status),
+      next: next_page,
+      items: @replies.map { |status| status.local ? status : status.uri }
+    )
+
+    return page if page_requested?
+
+    ActivityPub::CollectionPresenter.new(
+      id: account_status_replies_url(@account, @status),
+      type: :unordered,
+      first: page
+    )
+  end
+
+  def page_requested?
+    params[:page] == 'true'
+  end
+
+  def next_page
+    only_other_accounts = !(@replies&.last&.account_id == @account.id && @replies.size == DESCENDANTS_LIMIT)
+    account_status_replies_url(
+      @account,
+      @status,
+      page: true,
+      min_id: only_other_accounts && !page_params[:only_other_accounts] ? nil : @replies&.last&.id,
+      only_other_accounts: only_other_accounts
+    )
+  end
+
+  def page_params
+    params_slice(:only_other_accounts, :min_id).merge(page: true)
+  end
+end