# encoding: utf-8

module Uuids

  # The module contains ActiveRecord based models.
  module Models

    # The model describes uuids assigned to corresponding records.
    # @see http://www.ietf.org/rfc/rfc4122.txt RFC4122 standard.
    # @see https://en.wikipedia.org/wiki/Universally_unique_identifier Wikipedia
    # article.
    #
    # @example
    #   # Creates the uuid
    #   uuid = Uuids::Models::Uuid.create! record: some_record
    #
    #   # Finds a record by uuid
    #   Uuid.find_by_value(uuid.value).record # => some_record
    #
    #   # Reassigns a uuid to another record
    #   uuid.update_attributes! record: another_record
    #
    class Uuid < ActiveRecord::Base
      self.table_name = :uuids_uuids

      # @!attribute value
      # The uuid value as defined in RFC4122
      # @example The value can be set explicitly
      #   uuid = Uuids::Models::Uuid.new(
      #     value: "d679a46d-13b2-0a78-ad7b-20381441322c"
      #   )
      #   uuid.value # => "d679a46d-13b2-0a78-ad7b-20381441322c"
      # @example When not set, the value is assigned by default
      #   uuid = Uuids::Models::Uuid.new
      #   uuid.value # => "51f7314a-90e8-04db-65d6-8a6de83499de"
      # @return [String] The uuid value.

      UUID = /\A\h{8}-\h{4}-\h{4}-\h{4}-\h{12}\z/
      attr_readonly :value
      validates :value, format: { with: UUID }, allow_nil: true

      # @!attribute record
      # The record the uuid is assigned to.
      # @return [ActiveRecord::Base] The record the uuid is assigned to.

      belongs_to :record, polymorphic: true
      validate   :record_present?

      after_initialize :set_default_value
      before_destroy   :forbid_destruction

      private

      # Validates record presence with a custom error message.
      def record_present?
        return if record
        errors.add :record, :blank, uuid: value
      end

      # Sets a new value by default
      def set_default_value
        self.value = SecureRandom.uuid unless value
      end

      # Forbids destruction of the record.
      def forbid_destruction
        errors.add :base, :destruction_forbidden
        false
      end
    end
  end
end