active_model_serializers/lib/active_model/serializer/adapter.rb

module ActiveModel
  class Serializer
    class Adapter
      extend ActiveSupport::Autoload
      autoload :Json
      autoload :Null
      autoload :JsonApi

      attr_reader :serializer

      def initialize(serializer, options = {})
        @serializer = serializer
        @options = options
      end

      def serializable_hash(options = {})
        raise NotImplementedError, 'This is an abstract method. Should be implemented at the concrete adapter.'
      end

      def as_json(options = {})
        if fields = options.delete(:fields)
          options[:fieldset] = ActiveModel::Serializer::Fieldset.new(fields, serializer.json_key)
        end

        serializable_hash(options).to_json
      end
    end
  end
end