permissions to prevent updates we don't want

config ∕ initializers ∕ rights_metadata_validation_override.rb

require 'hydra/datastream/rights_metadata'
module Hydra
  module Datastream
    class RightsMetadata < ActiveFedora::NokogiriDatastream
      class PermissionsViolation < ::RuntimeError
      end
      # Validates permissions changes
      def validate_permissions(type, actor, access_level)
        # do some validations, throw some errors, whatever
        raise PermissionsViolation if [type, actor, access_level] == [:person, "person123", "edit"]
      end
      # Wraps permissions with validation
      old_permissions = instance_method(:permissions)
      define_method(:permissions) do |selector, new_access_level=nil|
        type = selector.keys.first.to_sym
        actor = selector.values.first
        validate_permissions(type, actor, new_access_level)
        old_permissions.bind(self).call(selector, new_access_level)
      end
    end
  end
end

## to test this in rails console:
# rm = Hydra::Datastream::RightsMetadata.new(nil, 'rightsMd')
# rm.permissions({:person=>"person123"}, "edit")
Hydra::Datastream::RightsMetadata::PermissionsViolation: Hydra::Datastream::RightsMetadata::PermissionsViolation