class GraphQL::StaticValidation::ComplexityValidator
  include GraphQL::StaticValidation::Message::MessageHelper

  def initialize(max_fields:, list_multiplier:)
    @max_fields = max_fields
    @list_multiplier = list_multiplier
  end

  def validate(context)
    visitor = context.visitor
    complexity = 0
    visitor[GraphQL::Language::Nodes::Field] << -> (node, parent) {
      field_type = field_definition.type
      if field_type.kind.list?
        complexity += list_multiplier
      else
        complexity += 1
      end
    }

    visitor[GraphQL::Language::Nodes::Document].exit << -> (node, parent) {
      if complexity > @max_fields
        context.errors << message("This query is too complex. Request fewer fields.", node)
      end
    }
  end
end