class ElasticGraph::GraphQL::DatastoreQuery::DocumentPaginator

def effective_size
  individual_docs_needed ? paginator.requested_page_size : 0
end

def effective_sort
  return [] unless effective_size > 0
  paginator.search_in_reverse? ? reverse_sort : sort
end

def reverse_sort
  @reverse_sort ||= sort.map do |sort_clause|
    sort_clause.transform_values do |options|
      {
        "order" => DIRECTION_OPPOSITES.fetch(options.fetch("order")),
        "missing" => MISSING_OPPOSITES.fetch(options.fetch("missing"))
      }
    end
  end
end

def search_after
  paginator.search_after&.then do |cursor|
    decoded_cursor_factory.sort_fields.map do |field|
      cursor.sort_values.fetch(field) do
        raise ::GraphQL::ExecutionError, "`#{cursor.encode}` is not a valid cursor for the current `#{schema_element_names.order_by}` argument."
      end
    end
  end
end

def sort
  @sort ||= sort_clauses.map do |clause|
    clause.transform_values do |options|
      # As per the Elasticsearch docs[^1] missing/null values get sorted last by default, but we can control
      # it here. We want to control it here to make our sorting behavior more consistent in a couple ways:
      #
      # 1. We want _document_ sorting and _aggregation_ sorting to behave the same. Aggregation sorting puts
      #    missing value buckets first when sorting ascending and last when sorting descending[^2]. Note that in
      #    Elasticsearch 7.16[^3] and above, you can control if missing buckets go first or last, but below that
      #    version you have no control. Here we match that behavior.
      # 2. Clients are likely to expect that descending sorting will produce a list in reverse order from what
      #    ascending sorting produces, but with the default behavior (missing/null values get sorted last), this
      #    is not the case. We have to use the opposite `missing` option when the `order` is the opposite.
      #
      # [^1]: https://www.elastic.co/guide/en/elasticsearch/reference/7.10/sort-search-results.html#_missing_values
      # [^2]: https://www.elastic.co/guide/en/elasticsearch/reference/7.10/search-aggregations-bucket-composite-aggregation.html#_missing_bucket
      # [^3]: https://www.elastic.co/guide/en/elasticsearch/reference/7.16/search-aggregations-bucket-composite-aggregation.html#_missing_bucket
      missing = (options.fetch("order") == "asc") ? "_first" : "_last"
      options.merge({"missing" => missing})
    end
  end
end

def to_datastore_body
  {
    size: effective_size,
    sort: effective_sort,
    search_after: search_after,
    track_total_hits: total_document_count_needed
  }.reject { |key, value| Array(value).empty? }
end