Validates that only allowed values are added to an array field.

array_validator.rb

# frozen_string_literal: true

class ArrayValidator < ActiveModel::EachValidator
  ERROR_MESSAGE = 'An array must be supplied in the :is_subset_of option ' \
                  'of the configuration hash'
                  
  def validate_each(record, attribute, value)
    return unless value.is_a? Array

    return if (value - other).empty?

    record.errors.add attribute, :inclusion
  end

  def check_validity!
    return if other.is_a? Array

    raise ArgumentError, ERROR_MESSAGE
  end

  private

  def other
    @other ||= options[:is_subset_of]
  end
end