Module to use the Gerund pattern on ActiveRecord models

gerund.rb

# frozen_string_literal: true

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

  module ClassMethods
    delegate :model_name,
      :sti_name,
      :finder_needs_type_condition?,
      :_to_partial_path,
      to: :superclass
  end

  # Not great to monkeypatch this, but it's the least amount of code
  # that does what we want. The issue here is #becomes is super handy
  # with gerunds, but the instance returned from #becomes has @attributes
  # literally as a pointer to the original attributes hash. This is a
  # problem if our subclass defines more attributes with the ::attribute method
  # - assignment won't work because the parent instance attributes won't have
  # the subclass' attributes defined. This monkeypatch fixes that, just in time
  # for anything that depends on these attributes, including `after_initialize`
  # callbacks.
  def _run_initialize_callbacks
    extra_attrs = self.class._default_attributes.keys - @attributes.keys
    # Copy over any extra attributes from the gerund to the original attribute
    # set. Personally I'd like it to be a new set of attributes, but our code
    # accidentally depends on this in a couple places, and I guess I'd rather not
    # have it two ways so let's do it the way Rails ships with.
    extra_attrs.each do |attr|
      @attributes.instance_variable_get(:@attributes)[attr] =
        self.class._default_attributes.instance_variable_get(:@attributes)[attr]
    end
    super
  end

  # GlobalID depends on the model to get class_name, rather than passing
  # it in directly. Maybe someday we can try to get GlobalID to be easier
  # to work with in this way; until then, this works.
  def to_global_id(*args)
    becomes(self.class.superclass).to_global_id(*args)
  end
  alias :to_gid :to_global_id
end