Initial refactoring

Gemfile

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+source 'https://rubygems.org'
+gem 'minitest', '~> 5.4'

Gemfile.lock

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+GEM
+  remote: https://rubygems.org/
+  specs:
+    minitest (5.14.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  minitest (~> 5.4)
+
+BUNDLED WITH
+   2.1.4

lib/bottles.rb

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+class CountdownSong
+  attr_reader :verse_template, :max, :min
+
+  def initialize(verse_template:, max: 999999, min: 0)
+    @verse_template = verse_template
+    @max, @min = max, min
+  end
+
+  def song
+    verses(max, min)
+  end
+
+  def verses(upper, lower)
+    upper.downto(lower).collect {|i| verse(i)}.join("\n")
+  end
+
+  def verse(number)
+    verse_template.lyrics(number)
+  end
+end
+
+
+class BottleVerse
+  def self.lyrics(number)
+    new(BottleNumber.new(number)).lyrics
+  end
+
+  attr_reader :bottle_number
+
+  def initialize(bottle_number)
+    @bottle_number = bottle_number
+  end
+
+  def lyrics
+    "#{bottle_number} of beer on the wall, ".capitalize +
+    "#{bottle_number} of beer.\n" +
+    "#{bottle_number.action}, " +
+    "#{bottle_number.successor} of beer on the wall.\n"
+  end
+end
+
+
+class BottleNumber
+  attr_reader :number
+  def initialize(number)
+    @number = number
+  end
+
+  def to_s
+    "#{quantity} #{container}"
+  end
+
+  def quantity
+    BOTTLE_NUMBER_DEFAULTS[number]&.[](:quantity) || number.to_s
+  end
+
+  def container
+    BOTTLE_NUMBER_DEFAULTS[number]&.[](:container) || "bottles"
+  end
+
+  def action
+    BOTTLE_NUMBER_DEFAULTS[number]&.[](:action) || "Take #{pronoun} down and pass it around"
+  end
+
+  def pronoun
+    BOTTLE_NUMBER_DEFAULTS[number]&.[](:pronoun) || "one"
+  end
+
+  def successor
+    BOTTLE_NUMBER_DEFAULTS[number]&.[](:successor) ?  BottleNumber.new(BOTTLE_NUMBER_DEFAULTS[number]&.[](:successor)) : BottleNumber.new(number - 1)
+  end
+end
+
+BOTTLE_NUMBER_DEFAULTS = {
+  0 => {
+    quantity: "no more",
+    action: "Go to the store and buy some more",
+    successor: 99
+  },
+  1 => {
+    container: "bottle",
+    pronoun: "it"
+  },
+  6 => {
+    quantity: "1",
+    container: "six-pack"
+  }
+}
+
+pp BOTTLE_NUMBER_DEFAULTS[9]&.[](:quantity)

test/bottles_test.rb

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+gem 'minitest', '~> 5.4'
+require 'minitest/autorun'
+require 'minitest/pride'
+require_relative '../lib/bottles'
+
+module VerseRoleTest
+  def test_plays_verse_role
+    assert_respond_to @role_player, :lyrics
+  end
+end
+
+class VerseFake
+  def self.lyrics(number)
+    "This is verse #{number}.\n"
+  end
+end
+
+class VerseFakeTest < Minitest::Test
+  include VerseRoleTest
+
+  def setup
+    @role_player = VerseFake
+  end
+end
+
+
+class BottleVerseTest < Minitest::Test
+  include VerseRoleTest
+
+  def setup
+    @role_player = BottleVerse
+  end
+
+  def test_verse_general_rule_upper_bound
+    expected =
+      "99 bottles of beer on the wall, " +
+      "99 bottles of beer.\n" +
+      "Take one down and pass it around, " +
+      "98 bottles of beer on the wall.\n"
+    assert_equal expected, BottleVerse.lyrics(99)
+  end
+
+  def test_verse_general_rule_lower_bound
+    expected =
+      "3 bottles of beer on the wall, " +
+      "3 bottles of beer.\n" +
+      "Take one down and pass it around, " +
+      "2 bottles of beer on the wall.\n"
+    assert_equal expected, BottleVerse.lyrics(3)
+  end
+
+  def test_verse_7
+    expected =
+      "7 bottles of beer on the wall, " +
+      "7 bottles of beer.\n" +
+      "Take one down and pass it around, " +
+      "1 six-pack of beer on the wall.\n"
+    assert_equal expected, BottleVerse.lyrics(7)
+  end
+
+  def test_verse_6
+    expected =
+      "1 six-pack of beer on the wall, " +
+      "1 six-pack of beer.\n" +
+      "Take one down and pass it around, " +
+      "5 bottles of beer on the wall.\n"
+    assert_equal expected, BottleVerse.lyrics(6)
+  end
+
+  def test_verse_2
+    expected =
+      "2 bottles of beer on the wall, " +
+      "2 bottles of beer.\n" +
+      "Take one down and pass it around, " +
+      "1 bottle of beer on the wall.\n"
+    assert_equal expected, BottleVerse.lyrics(2)
+  end
+
+  def test_verse_1
+    expected =
+      "1 bottle of beer on the wall, " +
+      "1 bottle of beer.\n" +
+      "Take it down and pass it around, " +
+      "no more bottles of beer on the wall.\n"
+     assert_equal expected, BottleVerse.lyrics(1)
+  end
+
+  def test_verse_0
+    expected =
+      "No more bottles of beer on the wall, " +
+      "no more bottles of beer.\n" +
+      "Go to the store and buy some more, " +
+      "99 bottles of beer on the wall.\n"
+    assert_equal expected, BottleVerse.lyrics(0)
+  end
+end
+
+
+class CountdownSongTest < Minitest::Test
+  def test_verse
+    expected = "This is verse 500.\n"
+    assert_equal(
+      expected,
+      CountdownSong.new(verse_template: VerseFake)
+        .verse(500))
+  end
+
+  def test_verses
+    expected =
+     "This is verse 99.\n" +
+     "\n" +
+     "This is verse 98.\n" +
+     "\n" +
+     "This is verse 97.\n"
+    assert_equal(
+      expected,
+      CountdownSong.new(verse_template: VerseFake)
+        .verses(99, 97))
+  end
+
+  def test_song
+    expected =
+      "This is verse 47.\n" +
+      "\n" +
+      "This is verse 46.\n" +
+      "\n" +
+      "This is verse 45.\n" +
+      "\n" +
+      "This is verse 44.\n" +
+      "\n" +
+      "This is verse 43.\n"
+    assert_equal(
+      expected,
+      CountdownSong.new(verse_template: VerseFake,
+                        max: 47,
+                        min: 43)
+        .song)
+  end
+end