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to Twelve Days in the Ruby Track

Published at May 07 2019 · 0 comments
Instructions
Test suite
Solution

In this exercise, you'll create a class to output the lyrics to the traditional English Christmas carol "The Twelve Days of Christmas" (complete lyrics below).

In this song, each verse is built on top of the previous verses in a repeating pattern. Can you use Ruby to build up the repeated lyrics programmatically?

Note on testing: Unlike previous exercises, this exercise doesn't include an extensive set of test cases. Instead, there is an "acceptance" test to make sure that the final output is correct. A file called song.txt is included with the exercise, but this is to be used for the acceptance test to validate the solution, not as part of the solution itself.

On the first day of Christmas my true love gave to me: a Partridge in a Pear Tree.

On the second day of Christmas my true love gave to me: two Turtle Doves, and a Partridge in a Pear Tree.

On the third day of Christmas my true love gave to me: three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the fourth day of Christmas my true love gave to me: four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the fifth day of Christmas my true love gave to me: five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the sixth day of Christmas my true love gave to me: six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the seventh day of Christmas my true love gave to me: seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the eighth day of Christmas my true love gave to me: eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the ninth day of Christmas my true love gave to me: nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the tenth day of Christmas my true love gave to me: ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the eleventh day of Christmas my true love gave to me: eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the twelfth day of Christmas my true love gave to me: twelve Drummers Drumming, eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

For installation and learning resources, refer to the Ruby resources page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby twelve_days_test.rb

To include color from the command line:

ruby -r minitest/pride twelve_days_test.rb

Source

Wikipedia http://en.wikipedia.org/wiki/The_Twelve_Days_of_Christmas_(song)

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

twelve_days_test.rb

require 'minitest/autorun'
require_relative 'twelve_days'

class TwelveDaysTest < Minitest::Test
  # This test is an acceptance test.
  #
  # If you find it difficult to work the problem with so much
  # output, go ahead and add a `skip`, and write whatever
  # unit tests will help you. Then unskip it again
  # to make sure you got it right.
  # There's no need to submit the tests you write, unless you
  # specifically want feedback on them.
  def test_the_whole_song
    song_file = File.expand_path('../song.txt', __FILE__)
    expected = IO.read(song_file)
    assert_equal expected, TwelveDays.song
  end
end
#  frozen_string_literal: true

module TwelveDays
  CARDINALS =
    Hash.new { |hash, key| hash[key] = key.gsub(/th\z/, "") }.tap do |hash|
      hash["first"] = "a"
      hash["second"] = "two"
      hash["third"] = "three"
      hash["fifth"] = "five"
      hash["eighth"] = "eight"
      hash["ninth"] = "nine"
      hash["twelfth"] = "twelve"
    end
  private_constant :CARDINALS
  COMMA = ", "
  private_constant :COMMA
  COMMA_AND = ", and "
  private_constant :COMMA_AND
  DECLARATION_OF_RECEIPT =
    "On the %<day>s day of Christmas my true love gave to me: "
  private_constant :DECLARATION_OF_RECEIPT
  # Empty song holds an array for the generated song verses, and an array for
  # the "extra gifts" that need to be added to each consecutive day.
  EMPTY_SONG = [[], []].freeze
  private_constant :EMPTY_SONG
  GIFTS = [
    " Partridge in a Pear Tree",
    " Turtle Doves",
    " French Hens",
    " Calling Birds",
    " Gold Rings",
    " Geese-a-Laying",
    " Swans-a-Swimming",
    " Maids-a-Milking",
    " Ladies Dancing",
    " Lords-a-Leaping",
    " Pipers Piping",
    " Drummers Drumming"
  ].freeze
  private_constant :GIFTS
  NEWLINE = "\n"
  private_constant :NEWLINE
  ORDINALS = %w[
    first
    second
    third
    fourth
    fifth
    sixth
    seventh
    eighth
    ninth
    tenth
    eleventh
    twelfth
  ].freeze
  private_constant :ORDINALS
  PERIOD = "."
  private_constant :PERIOD

  module_function

  def song
    ORDINALS
      .zip(GIFTS)
      .each_with_object(EMPTY_SONG.dup, &method(:add_verse_to_song))
      .first
      .join(NEWLINE)
  end

  def add_verse_to_song((day, gift), (song, extra_gifts))
    current_gift = CARDINALS[day] + gift
    todays_gifts = current_gift + extra_gifts.join
    add_current_gift_to_extra_gifts(current_gift, extra_gifts)
    song << verse(day, todays_gifts)
  end
  private_class_method :add_verse_to_song

  def add_current_gift_to_extra_gifts(current_gift, extra_gifts)
    if extra_gifts.empty?
      extra_gifts << COMMA_AND + current_gift
    else
      extra_gifts.prepend(COMMA + current_gift)
    end
  end
  private_class_method :add_current_gift_to_extra_gifts

  def verse(day, todays_gifts)
    format(DECLARATION_OF_RECEIPT, day: day) + todays_gifts + PERIOD + NEWLINE
  end
  private_class_method :verse
end

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