Return human age by date of birth

action_view.rb

module ActionView::Helpers::DateHelper

  def age(date_of_birth, **options)
    from_time = normalize_distance_of_time_argument_to_time(date_of_birth)
    to_time = normalize_distance_of_time_argument_to_time(options.delete(:to_time) || Time.now)

    from_time, to_time = to_time, from_time if from_time > to_time
    distance_in_minutes = ((to_time - from_time) / 60.0).round

    case distance_in_minutes
    when 0...43200  # 0 to 30 days
      "#{(distance_in_minutes.to_f / 1440.0).round} days"
    when 43200...MINUTES_IN_YEAR  # 30 to 365 days
      months = (distance_in_minutes.to_f / 43200.0).round
      [months, "month".pluralize(months)].join(" ")
    else  # start accounting for leap years...
      from_year = from_time.year
      from_year += 1 if from_time.month >= 3
      to_year = to_time.year
      to_year -= 1 if to_time.month < 3
      leap_years = (from_year > to_year) ? 0 : (from_year..to_year).count{ |x| Date.leap?(x) }
      minute_offset_for_leap_year = leap_years * 1440

      # Discount the leap year days when calculating year distance.
      # e.g. if there are 20 leap year days between 2 dates having the same day and month then based on the 365 days
      # calculation, the distance in years will come out to "over 80 years" when in written English it would read
      # better as "about 80 years".

      minutes_with_offset = distance_in_minutes - minute_offset_for_leap_year
      remainder = minutes_with_offset % MINUTES_IN_YEAR
      distance_in_years = minutes_with_offset.div MINUTES_IN_YEAR

      if minutes_with_offset < (MINUTES_IN_YEAR * 2)
        "#{(minutes_with_offset.to_f / 43200.0).round} months"
      elsif remainder < MINUTES_IN_QUARTER_YEAR || remainder < MINUTES_IN_THREE_QUARTERS_YEAR
        "#{distance_in_years} years"
      else
        "#{distance_in_years + 1} years"
      end
    end
  end

end