bottles.rb

class Bottles
  attr_reader :where, :substance

  def initialize(substance='of beer', where='on the wall')
    @substance = substance
    @where = where
  end

  def verse bottle_number
    next_bottle_number = bottle_number - 1
    next_bottle_number = 99 if next_bottle_number == -1
    "#{how_many(bottle_number).capitalize} #{container bottle_number} #{substance} #{where}, " +
    "#{how_many bottle_number} #{container bottle_number} #{substance}.\n" +
    "#{what_to_do bottle_number} #{how_many(next_bottle_number)} #{container(next_bottle_number)} " +
    "#{substance} #{where}.\n"
  end

  def verses begin_number, end_number
    begin_number.downto(end_number).map do |n|
      verse(n)
    end.join("\n")
  end

  def song
    starting_quanity = 99
    ending_quanity = 0
    verses(starting_quanity, ending_quanity)
  end

  private
  def container quantity
    case quantity
    when 1
      "bottle"
    when 6
      "sixpack"
    else
      "bottles"
    end
  end

  def pronoun quantity
    quantity == 1 ? "it" : "one"
  end

  def how_many quantity
    case quantity
    when 0
      "no more"
    when 6
      "a"
    else
      quantity.to_s
    end
  end

  def what_to_do quantity
    if quantity == 0
      "Go to the store and buy some more,"
    else
      "Take #{pronoun quantity} down and pass it around,"
    end
  end
end


class SixPack < Bottles
  def container quantity
    case quantity
    when 6
      "sixpack"
    else
      super(quantity)
    end
  end

  def how_many quantity
    case quantity
    when 6
      "a"
    else
      super(quantity)
    end
  end
end