Find time difference(in months,years,weeks..etc) between two dates.

time_difference.rb

=begin

 Time difference (duration) in year, quarter, month, bi-week, week and day.
 
 Usages:
   TimeDifference.between(start_date, end_date).in_months
   TimeDifference.between(start_date, end_date).in_years
   
=end

class TimeDifference

  private_class_method :new

  def self.between(start_date, end_date)
    new(start_date, end_date)
  end

  def in_years
    in_component("1.year")
  end

  def in_semi_year
    in_component("6.months")
  end

  def in_quarters
    in_component("3.months")
  end

  def in_months
    in_component("1.month")
  end

  def in_bi_weeks
    in_component("2.weeks")

  end

  def in_weeks
    in_component("1.week")
  end

  def in_days
    (@end_date - @start_date).to_i
  end

  private

  def initialize(start_date, end_date)
    @start_date = start_date
    @end_date = end_date
  end

  def in_component(periods)
    difference = 0
    next_dt = eval("@start_date + #{periods}")

    while next_dt <= @end_date do
      difference += 1
      next_dt = eval("next_dt + #{periods}")
    end

    difference
  end

end