advance_working_days.rb

class Date
  
  #hard coded to GB holidays if Holidays gem is installed.
  def advance_working_days(working_dates_required)
    return self if working_dates_required == 0
    
    if Gem.available?('holidays')
      require 'holidays'
      require 'holidays/gb'
    end

    new_date = self.dup
    direction = working_dates_required > 0 ? 1 : -1
    working_dates_stepped = 0
    
    until working_dates_required == working_dates_stepped
      #you probably never want to advance more than 100 working days etc, so this is a sign somethings up.
      raise "looping on #{self.inspect} #{working_dates_required}" if(self-new_date).abs > 100
      
      #step a day
      new_date += direction
      
      #determine if new day is a weekend/holiday
      weekend = [0,6].include?(new_date.wday)
      holiday = defined?(Holidays) ? Holidays.on(new_date, :gb).not_blank? : false
      
      #consider it a working step if its not
      working_dates_stepped += direction unless (weekend || holiday)
    end
    
    new_date
  end
  
end

describe Date do

  describe "#advance_working_days" do
    
    context "skips weekends" do
      # pop over the weekend
      it "Fri, 19 Mar 2010 + 1 working days -> Mon, 22 Mar 2010" do
        Date.parse('2010-03-19').advance_working_days(1).should == Date.parse('2010-03-22')
      end
      
      # two weeks
      it "Fri, 19 Mar 2010 + 6 working days -> Mon, 29 Dec 2010" do
        Date.parse('2010-03-19').advance_working_days(6).should == Date.parse('2010-03-29')
      end
      
    end
    
    context "holidays" do
      
      # skip christmas eve, christmas, boxing day
      it "Thu, 23 Dec 2010 + 3 working days -> Tue, 28 Dec 2010" do
        Date.parse('2010-12-23').advance_working_days(3).should == Date.parse('2010-12-28')
      end
      
    end
    
  end
  
end