json_serialize.rb

class JsonSerialize
  include ActiveModel::Model
  include ActiveModel::Attributes
  include ActiveModel::Serializers::JSON

  def initialize(attributes)
    super()
    attributes.each do |key, value|
      self.public_send("#{key}=", value)
    end
  end

  def self.from(**model)
    new(model.attributes)
  end

  def self.from_many(*models)
    Array.wrap(models).map { |model| from(model) }
  end
end

class PaginationSerializer < JsonSerialize
  attributes :total_count, :integer
  attributes :total_pages, :integer
  attributes :page, :integer
  attributes :items, :integer

  def self.from_pagination(models, item_class:)
    new(
      total_count: models.total_count,
      total_pages: models.total_pages,
      page: models.page,
      items: item_class.from_many(models)
    )
  end
end

class ItemSerializer < JsonSerialize
  attribute :name, :string
  attribute :price, :integer

  def is_public
    published_at.present?
  end

  def attributes
    super.merge(is_public:)
  end
end

ItemSerializer.new(name: 'a', price: 1000)
ItemSerializer.new(name: 'a', price: '1000')
ItemSerializer.new(name: 'a', price: 'aaaa')