"Translation" of Kent Back's 99 bottles of beer Smalltalk version: https://leftsideagile.com/index.php?post/2020/02/16/The-Beginning-of-Extreme-Programming

bob.rb

class Verse
  attr_accessor :stream, :count

  def self.verse(count, stream)
    case
    when count  < 0 then NegativeVerse.new
    when count == 0 then UltimateVerse.new(stream)
    when count == 1 then PenultimateVerse.new(stream)
    else PrecedingVerse.new(stream).tap { |pv| pv.count = count }
    end
  end

  def self.sing(count)
    stream = ''
    verse(count, stream).sing
    puts stream
  end

  def initialize(stream)
    self.stream = stream
    super()
  end

  def sing
    sing_verse
    next_verse.sing
  end

  def sing_verse
    bottles_of_beer_on_the_wall
    bottles_of_beer
    take_one_down
    next_verse_bottles_of_beer_on_the_wall
    stream << "\n"
  end
  
  def bottles_of_beer_on_the_wall
    count_bottles
    stream << ' of beer on the wall '
  end

  def count_bottles
    stream << bottle_count_string
    stream << ' '
    stream << bottles_string
  end

  def bottle_count_string
    count.to_s
  end

  def bottles_string
    'bottles'
  end

  def bottles_of_beer
    count_bottles
    stream << ' of beer '
  end

  def take_one_down
    stream << 'Take one down and pass it around '
  end

  def next_verse_bottles_of_beer_on_the_wall
    next_verse.bottles_of_beer_on_the_wall
  end

  def next_verse
    self.class.verse(count - 1, stream)
  end
end

class NegativeVerse
  def sing
    'Do nothing'
  end
end

class UltimateVerse < Verse
  def count
    0
  end

  def bottle_count_string
    'No'
  end

  def next_verse_bottles_of_beer_on_the_wall
    bottles_of_beer_on_the_wall
  end

  def take_one_down
    stream << 'There are no more to pass it around '
  end
end

class PenultimateVerse < Verse
  def bottles_string
    'bottle'
  end

  def count
    1
  end

  def take_one_down
    stream << 'Take it down and pass it around '
  end
end

class PrecedingVerse < Verse
  def take_one_down
    stream << 'Take one down and pass it around '
  end
end

Verse.sing(99)