Calculate beginning and end of payroll given an arbitrary date

payroll.rb

def beginning_of_payroll(given_date)
  payroll_start_seed = Date.new(2011,12,02)
  given_date - ( (given_date - payroll_start_seed).abs % 14 )
end

def end_of_payroll(given_date)
  beginning_of_payroll(given_date) + 13
end