fast_jsonapi formatter for Grape

fast_jsonapi.rb

module Grape
  module Formatter
    module FastJsonapi

      class << self
        def call(object, _env)
          return object if object.is_a?(String)
          return ::Grape::Json.dump(serialize(object)) if serializable?(object)
          return object.to_json if object.respond_to?(:to_json)
          ::Grape::Json.dump(object)
        end

        private

        def serializable?(object)
          object.respond_to?(:serializable_hash) || object.respond_to?(:to_a) && object.all? { |o| o.respond_to? :serializable_hash } || object.is_a?(Hash)
        end

        def serialize(object)
          if object.respond_to? :serializable_hash
            serializable_object(object).serializable_hash
          elsif object.respond_to?(:to_a) && object.all? { |o| o.respond_to? :serializable_hash }
            fast_jsonapi_serializable(object).serializable_hash || object.map(&:serializable_hash)
          elsif object.is_a?(Hash)
            h = {}
            object.each_pair do |k, v|
              h[k] = serialize(v)
            end
            h
          else
            object
          end
        end

        def serializable_object(object)
          fast_jsonapi_serializable(object) || object
        end

        def fast_jsonapi_serializable(object)
          serializable_class(object)&.new(object)
        end

        def serializable_class(object)
          (object.model_name.name + 'Serializer').safe_constantize
        end
      end
    end
  end
end