module ClassAttribute
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    # Based on `class_attribute` from Rails, without the options we don't use.
    # https://github.com/rails/rails/blob/main/activesupport/lib/active_support/core_ext/class/attribute.rb
    def tiny_class_attribute(name, default: nil)
      class_methods, methods = [], []

      methods << <<~RUBY
        def #{name}
          defined?(@#{name}) ? @#{name} : self.class.#{name}
        end
      RUBY

      class_methods << <<~RUBY
        def #{name}=(value)
          define_method(:#{name}) { value } if singleton_class?
          define_singleton_method(:#{name}) { value }
          value
        end
      RUBY

      methods << <<~RUBY
        attr_writer :#{name}
      RUBY

      location = caller_locations(1, 1).first
      class_eval(["class << self", *class_methods, "end", *methods].join(";").tr("\n", ";"), location.path, location.lineno)

      public_send(:"#{name}=", default)
    end
  end
end