First exercise of the 99 Bottles of Milk book

bottles.rb

class Bottles
  def song
    verses(99, 0)
  end

  def verses(start_index, end_index)
    numbers_of_bottles = (end_index..start_index).to_a.reverse
    all_verses = numbers_of_bottles.map{|number_of_bottles| verse(number_of_bottles)}
    all_verses.join("\n")
  end

  def verse(number_of_bottles)
    return no_bottles_verse if number_of_bottles == 0
    return one_bottles_verse if number_of_bottles == 1
    return two_bottles_verse if number_of_bottles == 2

    multiple_bottles_verse(number_of_bottles)
  end

  private

  def multiple_bottles_verse(number_of_bottles)
    <<-VERSE
#{number_of_bottles} bottles of beer on the wall, #{number_of_bottles} bottles of beer.
Take one down and pass it around, #{number_of_bottles - 1} bottles of beer on the wall.
VERSE
  end

  def two_bottles_verse
    <<-VERSE
2 bottles of beer on the wall, 2 bottles of beer.
Take one down and pass it around, 1 bottle of beer on the wall.
    VERSE
  end

  def one_bottles_verse
    <<-VERSE
1 bottle of beer on the wall, 1 bottle of beer.
Take it down and pass it around, no more bottles of beer on the wall.
    VERSE
  end

  def no_bottles_verse
    expected = <<-VERSE
No more bottles of beer on the wall, no more bottles of beer.
Go to the store and buy some more, 99 bottles of beer on the wall.
VERSE
  end

end