Struct representing a Duration

duration.rb

# composed_of :duration, class_name: 'Duration', mapping: %w(duration to_i), constructor: :parse, converter: :parse

class Duration
  SEPARATOR = ':'
  SECONDS = 0...60
  MINUTES = 0...60
  HOURS = 0...24

  include Comparable

  attr_reader :seconds, :minutes, :hours, :days

  def initialize(seconds, minutes = 0, hours = 0, days = 0)
    @seconds = Integer(seconds)
    raise ArgumentError, 'invalid seconds' unless SECONDS.include?(@seconds)
    @minutes = Integer(minutes)
    raise ArgumentError, 'invalid minutes' unless MINUTES.include?(@minutes)
    @hours = Integer(hours)
    raise ArgumentError, 'invalid hours' unless HOURS.include?(@hours)
    @days = Integer(days)
  end

  def self.from_seconds(total_seconds)
    total_seconds = Integer(total_seconds)
    seconds = total_seconds % SECONDS.size
    minutes = (total_seconds / SECONDS.size) % MINUTES.size
    hours = (total_seconds / (SECONDS.size * MINUTES.size)) % HOURS.size
    days = total_seconds / (SECONDS.size * MINUTES.size * HOURS.size)
    self.new(seconds, minutes, hours, days)
  end

  def self.parse(input)
    case input
    when self.class then input
    when Integer then from_seconds(input)
    else
      args = input.split(SEPARATOR).reverse
      raise 'invalid duration' if args.count > 4
      new(*args)
    end
  end

  def inspect
    "#<#{self.class.name} days: #{days}, hours: #{hours}, minutes: #{minutes}, seconds: #{seconds}>"
  end

  def total_seconds
    seconds +
    minutes * SECONDS.size +
    hours * MINUTES.size * SECONDS.size +
    days * HOURS.size * MINUTES.size * SECONDS.size
  end

  def to_i
    total_seconds
  end

  # Calculation and Comparison

  def <=>(other)
    return nil unless other.respond_to?(:to_i)
    self.to_i <=> other.to_i
  end

  def +(other)
    self.class.from_seconds(total_seconds + other.to_i)
  end

  def -(other)
    self.class.from_seconds(total_seconds - other.to_i)
  end

  def *(other)
    self.class.from_seconds(total_seconds * other)
  end

  def /(other)
    self.class.from_seconds(total_seconds / other)
  end

  def next
    self.class.from_seconds(total_seconds.next)
  end
  alias_method :succ, :next
end