beginning_of_fortnight method for Ruby on Rails

You might know that Rails provides a bunch of useful extensions to the Time class with methods like beginning_of_week, beginning_of_month, etc.

For my application (a thing with fortnightly billing periods) I wanted to define a beginning of fortnight method to consistently calculate the beginning (and end) of a fortnight. Here's how it ended up (both short and sweet):

	#
	# Extend ActiveSupport to provide a beginning_of_fortnight and an
	# end_of_fortnight method for the Time class
	#
	module ActiveSupport::CoreExtensions::Time::Calculations
	#
	# How many weeks since the beginning_of_week before unix time zero
	#
	def weeks_after_epoch
	((self - ::Time.at(0).beginning_of_week) / 1.week).to_i
	end
	#
	# The beginning of the current fortnight
	#
	# The choice of which week should begin a fortnight is arbitrary
	# If you want to flip it then change even? to odd? below
	#
	def beginning_of_fortnight
	# If there's been an even number of weeks since epoch use beginning of this week
	# If there's been an odd number of weeks since epoch use the beginning of last week
	(weeks_after_epoch.even? ? self : self - 1.week).beginning_of_week
	end
	#
	# The end of the current fortnight
	#
	def end_of_fortnight
	(beginning_of_fortnight + 13.days).end_of_day
	end
	end

view raw beginning_of_fortnight.rb hosted with ❤ by GitHub

(Note that there's no special reason to use epoch. Any other day would work just as well probably).

Does it work?

	[Development]>> puts Time.now; (-5..5).each { |w| t = Time.now + w.weeks; puts "now and #{'%2d'%w} weeks: #{t.beginning_of_fortnight} - #{t.end_of_fortnight}" }; nil
	Wed Oct 06 16:29:52 +1000 2010
	now and -5 weeks: Mon Aug 30 00:00:00 +1000 2010 - Sun Sep 12 23:59:59 +1000 2010
	now and -4 weeks: Mon Aug 30 00:00:00 +1000 2010 - Sun Sep 12 23:59:59 +1000 2010
	now and -3 weeks: Mon Sep 13 00:00:00 +1000 2010 - Sun Sep 26 23:59:59 +1000 2010
	now and -2 weeks: Mon Sep 13 00:00:00 +1000 2010 - Sun Sep 26 23:59:59 +1000 2010
	now and -1 weeks: Mon Sep 27 00:00:00 +1000 2010 - Sun Oct 10 23:59:59 +1000 2010
	now and 0 weeks: Mon Sep 27 00:00:00 +1000 2010 - Sun Oct 10 23:59:59 +1000 2010
	now and 1 weeks: Mon Oct 11 00:00:00 +1000 2010 - Sun Oct 24 23:59:59 +1000 2010
	now and 2 weeks: Mon Oct 11 00:00:00 +1000 2010 - Sun Oct 24 23:59:59 +1000 2010
	now and 3 weeks: Mon Oct 25 00:00:00 +1000 2010 - Sun Nov 07 23:59:59 +1000 2010
	now and 4 weeks: Mon Oct 25 00:00:00 +1000 2010 - Sun Nov 07 23:59:59 +1000 2010
	now and 5 weeks: Mon Nov 08 00:00:00 +1000 2010 - Sun Nov 21 23:59:59 +1000 2010
	=> nil

view raw Does it work? hosted with ❤ by GitHub

Put beginning_of_fortnight.rb in config/initializers.

Note that there is already a Numeric#fortnights method in ActiveSupport so we can use things like 2.fortnights without needing any extentions.