Date#in_time_zone monkeypatch for Rails 3

zones.rb

# this comes included in ActiveSupport 4+
unless ActiveSupport::VERSION::MAJOR > 3
  require 'date'

  module DateAndTime
    module Zones
      # Returns the simultaneous time in <tt>Time.zone</tt> if a zone is given or
      # if Time.zone_default is set. Otherwise, it returns the current time.
      #
      #   Time.zone = 'Hawaii'        # => 'Hawaii'
      #   DateTime.utc(2000).in_time_zone # => Fri, 31 Dec 1999 14:00:00 HST -10:00
      #   Date.new(2000).in_time_zone  # => Sat, 01 Jan 2000 00:00:00 HST -10:00
      #
      # This method is similar to Time#localtime, except that it uses <tt>Time.zone</tt> as the local zone
      # instead of the operating system's time zone.
      #
      # You can also pass in a TimeZone instance or string that identifies a TimeZone as an argument,
      # and the conversion will be based on that zone instead of <tt>Time.zone</tt>.
      #
      #   Time.utc(2000).in_time_zone('Alaska') # => Fri, 31 Dec 1999 15:00:00 AKST -09:00
      #   DateTime.utc(2000).in_time_zone('Alaska') # => Fri, 31 Dec 1999 15:00:00 AKST -09:00
      #   Date.new(2000).in_time_zone('Alaska')  # => Sat, 01 Jan 2000 00:00:00 AKST -09:00
      def in_time_zone(zone = ::Time.zone)
        time_zone = ::Time.find_zone! zone
        time = acts_like?(:time) ? self : nil

        if time_zone
          time_with_zone(time, time_zone)
        else
          time || self.to_time
        end
      end

      private

      def time_with_zone(time, zone)
        if time
          ActiveSupport::TimeWithZone.new(time.utc? ? time : time.getutc, zone)
        else
          ActiveSupport::TimeWithZone.new(nil, zone, to_time(:utc))
        end
      end
    end
  end

  class Date
    include DateAndTime::Zones
  end

  class DateTime
    include DateAndTime::Zones
  end

  class Time
    include DateAndTime::Zones
  end
end