mastodon/app/services/activitypub/fetch_all_replies_service.rb

# frozen_string_literal: true

class ActivityPub::FetchAllRepliesService < ActivityPub::FetchRepliesService
  include JsonLdHelper

  # Max number of replies to fetch - for a single post
  MAX_REPLIES = 500

  def call(status_uri, collection_or_uri, max_pages: 1, batch_id: nil, request_id: nil)
    @status_uri = status_uri

    super
  end

  private

  def filter_replies(items)
    # Find all statuses that we *shouldn't* update the replies for, and use that as a filter.
    # We don't assume that we have the statuses before they're created,
    # hence the negative filter -
    # "keep all these uris except the ones we already have"
    # instead of
    # "keep all these uris that match some conditions on existing Status objects"
    #
    # Typically we assume the number of replies we *shouldn't* fetch is smaller than the
    # replies we *should* fetch, so we also minimize the number of uris we should load here.
    uris = items.map { |item| value_or_id(item) }

    # Expand collection to get replies in the DB that were
    # - not included in the collection,
    # - that we have locally
    # - but we have no local followers and thus don't get updates/deletes for
    parent_id = Status.where(uri: @status_uri).pick(:id)
    unless parent_id.nil?
      unsubscribed_replies = Status
                             .where.not(uri: uris)
                             .where(in_reply_to_id: parent_id)
                             .unsubscribed
                             .pluck(:uri)
      uris.concat(unsubscribed_replies)
    end

    dont_update = Status.where(uri: uris).should_not_fetch_replies.pluck(:uri)

    # touch all statuses that already exist and that we're about to update
    Status.where(uri: uris).should_fetch_replies.touch_all(:fetched_replies_at)

    # Reject all statuses that we already have in the db
    uris = (uris - dont_update).take(MAX_REPLIES)

    Rails.logger.debug { "FetchAllRepliesService - #{@collection_or_uri}: Fetching filtered statuses: #{uris}" }
    uris
  end
end