Get the last Sunday of the Month

Question

I'm using Chronic to get the last Sunday of the month of any given year. It will gladly give me the n‌th Sunday, but not the last.

This works, but is not what I need:

Chronic.parse('4th sunday in march', :now => Time.local(2015,1,1))

This is what I need, but doesn't work:

Chronic.parse('last sunday in march', :now => Time.local(2015,1,1))

Is there any way around this apparent limitation?

UPDATE: I'm upvoting the two answers below because they're both good, but I've already implemented this in "pure Ruby" (in 2 lines of code, besides the require 'date' line), but I'm trying to demonstrate to management that Ruby is the right language to use to replace a Java codebase that is going away (and which had dozens of lines of code to compute this), and I told one manager that I probably could do it in one line of Ruby, and it would be readable and easy to maintain.

Answer 1

This works, and is as readable as I can get:

Chronic.parse('last sunday', now: Date.new(year,3,31))

Thanks to Ismael Abreu for the idea to just parse 'last sunday' and control the rest via the :now option.

UPDATE: Please also upvote Ismael's answer.

Answer 2

I am not sure about Chronic (I haven't heared about it before), but we can implement this in pure ruby :)

##
# returns a Date object being the last sunday of the given month/year
# month: integer between 1 and 12
def last_sunday(month,year)
  # get the last day of the month
  date = Date.new year, month, -1
  #subtract number of days we are ahead of sunday
  date -= date.wday
end

The last_sunday method can be used like this:

last_sunday 07, 2013
#=> #<Date: 2013-07-28 ((2456502j,0s,0n),+0s,2299161j)>

Answer 3

Reading the update in your question, I tried to come up with another answer using only a single line of ruby code (without using gems). How about this one?

##
# returns a Date object being the last sunday of the given month/year
# month: integer between 1 and 12
def last_sunday(month,year)
  # get the last day of the month, go back until we have a sunday
  Date.new(year, month, -1).downto(0).find(&:sunday?)
end

last_sunday 07, 2013
#=> #<Date: 2013-07-28 ((2456502j,0s,0n),+0s,2299161j)>

Answer 4

What about

Chronic.parse('last sunday', now: Chronic.parse('last day of march'))

Answer 5

It's a bit ugly, but you could simply try the 5th or 4th in that order:

d = [5,4].each do |i| 
  try = Chronic.parse("#{i}th sunday in march", :now => Time.local(2015,1,1))
  break try unless try.nil?
end
 => Sun Mar 29 12:30:00 +0100 2015

d = [5,4].each do |i| 
  try = Chronic.parse("#{i}th sunday in april", :now => Time.local(2015,1,1))
  break try unless try.nil?
end
 => Sun Apr 26 12:00:00 +0100 2015