module VestalVersions
  # The ActiveRecord model representing versions.
  class Version < ActiveRecord::Base
    include Comparable

    # Associate polymorphically with the parent record.
    belongs_to :versioned, :polymorphic => true

    # Order versions by number, ascending by default.
    default_scope :order => "#{table_name}.number ASC"

    # ActiveRecord::Base#changes is an existing method, so before serializing the +changes+ column,
    # the existing +changes+ method is undefined. The overridden +changes+ method pertained to 
    # dirty attributes, but will not affect the partial updates functionality as that's based on
    # an underlying +changed_attributes+ method, not +changes+ itself.
    undef_method :changes
    serialize :changes, Hash

    # In conjunction with the included Comparable module, allows comparison of version records
    # based on their corresponding version numbers, creation timestamps and IDs.
    def <=>(other)
      [number, created_at, id].map(&:to_i) <=> [other.number, other.created_at, other.id].map(&:to_i)
    end

    # Returns whether the version has a version number of 1. Useful when deciding whether to ignore
    # the version during reversion, as initial versions have no serialized changes attached. Helps
    # maintain backwards compatibility.
    def initial?
      number == 1
    end
  end
end