module Celluloid
  # Properties define inheritable attributes of classes, somewhat similar to
  # Rails cattr_*/mattr_* or class_attribute
  module Properties
    def property(name, opts = {})
      default   = opts.fetch(:default, nil)
      multi     = opts.fetch(:multi, false)
      ivar_name = "@#{name}".to_sym

      ancestors.first.send(:define_singleton_method, name) do |value = nil, *extra|
        if value
          value = value ? [value, *send(name), *extra].uniq : [] if multi
          instance_variable_set(ivar_name, value)
        elsif instance_variables.include?(ivar_name)
          instance_variable_get(ivar_name)
        elsif superclass.respond_to? name
          superclass.send(name)
        else
          default
        end
      end
    end
  end
end