module ActiveModel
  class Serializer
    # Holds all the meta-data about an association as it was specified in the
    # ActiveModel::Serializer class.
    #
    # @example
    #  class PostSerializer < ActiveModel::Serializer
    #     has_one :author, serializer: AuthorSerializer
    #     has_many :comments
    #  end
    #
    #  PostSerializer._reflections #=>
    #    # [
    #    #   HasOneReflection.new(:author, serializer: AuthorSerializer),
    #    #   HasManyReflection.new(:comments)
    #    # ]
    #
    # So you can inspect reflections in your Adapters.
    #
    Reflection = Struct.new(:name, :options) do
      # Build association. This method is used internally to
      # build serializer's association by its reflection.
      #
      # @param [Serializer] subject is a parent serializer for given association
      # @param [Hash{Symbol => Object}] parent_serializer_options
      #
      # @example
      #    # Given the following serializer defined:
      #    class PostSerializer < ActiveModel::Serializer
      #      has_many :comments, serializer: CommentSummarySerializer
      #    end
      #
      #    # Then you instantiate your serializer
      #    post_serializer = PostSerializer.new(post, foo: 'bar') #
      #    # to build association for comments you need to get reflection
      #    comments_reflection = PostSerializer._reflections.detect { |r| r.name == :comments }
      #    # and #build_association
      #    comments_reflection.build_association(post_serializer, foo: 'bar')
      #
      # @api private
      #
      def build_association(subject, parent_serializer_options)
        association_value = subject.send(name)
        reflection_options = options.dup
        serializer_class = ActiveModel::Serializer.serializer_for(association_value, reflection_options)

        if serializer_class
          begin
            serializer = serializer_class.new(
              association_value,
              serializer_options(parent_serializer_options, reflection_options)
            )
          rescue ActiveModel::Serializer::ArraySerializer::NoSerializerError
            reflection_options[:virtual_value] = association_value.try(:as_json) || association_value
          end
        elsif !association_value.nil? && !association_value.instance_of?(Object)
          reflection_options[:virtual_value] = association_value
        end

        Association.new(name, serializer, reflection_options)
      end

      private

      def serializer_options(parent_serializer_options, reflection_options)
        serializer = reflection_options.fetch(:serializer, nil)

        serializer_options = parent_serializer_options.except(:serializer)
        serializer_options[:serializer] = serializer if serializer
        serializer_options
      end
    end
  end
end