The house that Jack built

house.rb

class House
  def self.recite
    new.recite
  end

  attr_reader :start, :glue

  def initialize(start: "This is", glue: "that")
    @start = start
    @glue  = glue
  end

  def recite
    pieces.size.times.map { |n| verse(n+1) }.join("\n")
  end

  def verse(n)
    text = pieces.last(n).map.with_index do |(head, tail), idx|
      if idx == 0
        "#{start} #{tail}"
      else
        "#{glue} #{head} #{tail}"
      end
    end.join("\n")

    text << "\n"
  end

  def pieces
    [
      [ "",            "the horse and the hound and the horn" ],
      [ "belonged to", "the farmer sowing his corn" ],
      [ "kept",        "the rooster that crowed in the morn" ],
      [ "woke",        "the priest all shaven and shorn" ],
      [ "married",     "the man all tattered and torn" ],
      [ "kissed",      "the maiden all forlorn" ],
      [ "milked",      "the cow with the crumpled horn" ],
      [ "tossed",      "the dog" ],
      [ "worried",     "the cat" ],
      [ "killed",      "the rat" ],
      [ "ate",         "the malt" ],
      [ "lay in",      "the house that Jack built." ],
    ]
  end
end

house_test.rb

require 'minitest/autorun'
require_relative 'house'

class HouseTest < Minitest::Test

  def test_verse
    house = House.new

    {
      1 => "This is the house that Jack built.\n",
      2 => "This is the malt\nthat lay in the house that Jack built.\n",
    }.each do |n, expected|
      assert_equal expected, house.verse(n)
    end
  end

  def test_different_start
    house = House.new(start: "This is definitely")
    assert_equal "This is definitely the house that Jack built.\n", house.verse(1)
  end

  def test_rhyme
    expected = <<-RHYME
This is the house that Jack built.

This is the malt
that lay in the house that Jack built.

This is the rat
that ate the malt
that lay in the house that Jack built.

This is the cat
that killed the rat
that ate the malt
that lay in the house that Jack built.

This is the dog
that worried the cat
that killed the rat
that ate the malt
that lay in the house that Jack built.

This is the cow with the crumpled horn
that tossed the dog
that worried the cat
that killed the rat
that ate the malt
that lay in the house that Jack built.

This is the maiden all forlorn
that milked the cow with the crumpled horn
that tossed the dog
that worried the cat
that killed the rat
that ate the malt
that lay in the house that Jack built.

This is the man all tattered and torn
that kissed the maiden all forlorn
that milked the cow with the crumpled horn
that tossed the dog
that worried the cat
that killed the rat
that ate the malt
that lay in the house that Jack built.

This is the priest all shaven and shorn
that married the man all tattered and torn
that kissed the maiden all forlorn
that milked the cow with the crumpled horn
that tossed the dog
that worried the cat
that killed the rat
that ate the malt
that lay in the house that Jack built.

This is the rooster that crowed in the morn
that woke the priest all shaven and shorn
that married the man all tattered and torn
that kissed the maiden all forlorn
that milked the cow with the crumpled horn
that tossed the dog
that worried the cat
that killed the rat
that ate the malt
that lay in the house that Jack built.

This is the farmer sowing his corn
that kept the rooster that crowed in the morn
that woke the priest all shaven and shorn
that married the man all tattered and torn
that kissed the maiden all forlorn
that milked the cow with the crumpled horn
that tossed the dog
that worried the cat
that killed the rat
that ate the malt
that lay in the house that Jack built.

This is the horse and the hound and the horn
that belonged to the farmer sowing his corn
that kept the rooster that crowed in the morn
that woke the priest all shaven and shorn
that married the man all tattered and torn
that kissed the maiden all forlorn
that milked the cow with the crumpled horn
that tossed the dog
that worried the cat
that killed the rat
that ate the malt
that lay in the house that Jack built.
    RHYME

    assert_equal expected, House.recite
  end
end