base.rb

module Versioning
  class Base

    PREFIX = '__versioned'
    LENGTH = PREFIX.length

    def version
      raise ArgumentError.new('not defined')
    end

    def columns
      @columns ||= column_accessors.collect { |x| x[(LENGTH + 1)..-1] }.join(',')
    end

    def values
      column_accessors.collect { |column| self.send(column) }.join(',')
    end

    class << self
      def versioned_accessor(name, type, options = { })
        options.merge!({ length: 0, nil: true }) { |key, oldval, newval| oldval }

        name = name.to_sym
        column_name = "#{PREFIX}_#{name}".to_sym

        raise ArgumentError.new("Name #{name} is duplicated") if public_method_defined?(column_name)
        raise ArgumentError.new("Invalid type #{type}") unless [ :string, :integer ].include? type
        raise ArgumentError.new("Invalid length #{options[:length]}") if type == :string && options[:length].to_i <= 0

        define_method(column_name) do
          case type
          when :string
            instance_variable_get("@#{name}")
          when :integer
            value = instance_variable_get("@#{name}")
            options[:nil] ? value : value.to_i
          end
        end
        alias_method("#{name}", "#{column_name}")

        define_method("#{column_name}=") do |value|
          raise ArgumentError.new("Nil not supported for #{name}") if !options[:nil] && value.nil?

          return if value.nil? && options[:nil]

          case type
          when :integer
            instance_variable_set("@#{name}", value.to_i)
          when :string
            instance_variable_set("@#{name}", value[0..(options[:length] - 1)])
          end
        end
        alias_method("#{name}=", "#{column_name}=")

      end
    end

    private
    def column_accessors
      @column_accessors ||= methods.select { |x| x[0..(LENGTH - 1)] == PREFIX && x[-1..-1] != '=' }
    end

  end
end