TimeSpan formatter

time_span.rb

class TimeSpan
  MINUTE = 60
  HOUR   = 60 * MINUTE
  DAY    = 24 * HOUR

  def initialize(time)
    @span = time.to_i
  end

  def days
    @days ||= @span / DAY
  end

  def hours
    @hours ||= (@span - @days * DAY) / HOUR
  end

  def minutes
    @minutes = (@span - @days * DAY - @hours * HOUR) / MINUTE
  end

  def seconds
    @seconds ||= @span - @days * DAY - @hours * HOUR - @minutes * MINUTE
  end

  def to_s
    parts = []

    parts << format(days, "day")        if 0 < days
    parts << format(hours, "hour")      if 0 < hours
    parts << format(minutes, "minute")  if 0 < minutes
    parts << format(seconds, "second")  if 0 < seconds

    parts.join " "
  end

  def self.humanize(seconds)
    new(seconds).to_s
  end

  private

  def format(value, unit)
    "#{value} #{unit}#{'s' unless 1 == value}"
  end
end