Add dnd_character exercise (#1629)

* bin/configlet create --practice-exercise dnd-character
* Add dnd-character exercise difficulty
* Implement dnd-character test cases
* Add dnd_character.rb stub file
* Add example implementation of DndCharacter class

---------

Co-authored-by: KOTP <[email protected]>

config.json

@@ -284,6 +284,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "dnd-character",
+        "name": "D&D Character",
+        "uuid": "24f396d0-1fdf-4489-8976-8a3fb9a64adf",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "matrix",
         "name": "Matrix",

exercises/practice/dnd-character/.docs/instructions.md

@@ -0,0 +1,31 @@
+# Instructions
+
+For a game of [Dungeons & Dragons][dnd], each player starts by generating a character they can play with.
+This character has, among other things, six abilities; strength, dexterity, constitution, intelligence, wisdom and charisma.
+These six abilities have scores that are determined randomly.
+You do this by rolling four 6-sided dice and record the sum of the largest three dice.
+You do this six times, once for each ability.
+
+Your character's initial hitpoints are 10 + your character's constitution modifier.
+You find your character's constitution modifier by subtracting 10 from your character's constitution, divide by 2 and round down.
+
+Write a random character generator that follows the rules above.
+
+For example, the six throws of four dice may look like:
+
+- 5, 3, 1, 6: You discard the 1 and sum 5 + 3 + 6 = 14, which you assign to strength.
+- 3, 2, 5, 3: You discard the 2 and sum 3 + 5 + 3 = 11, which you assign to dexterity.
+- 1, 1, 1, 1: You discard the 1 and sum 1 + 1 + 1 = 3, which you assign to constitution.
+- 2, 1, 6, 6: You discard the 1 and sum 2 + 6 + 6 = 14, which you assign to intelligence.
+- 3, 5, 3, 4: You discard the 3 and sum 5 + 3 + 4 = 12, which you assign to wisdom.
+- 6, 6, 6, 6: You discard the 6 and sum 6 + 6 + 6 = 18, which you assign to charisma.
+
+Because constitution is 3, the constitution modifier is -4 and the hitpoints are 6.
+
+## Notes
+
+Most programming languages feature (pseudo-)random generators, but few programming languages are designed to roll dice.
+One such language is [Troll][troll].
+
+[dnd]: https://en.wikipedia.org/wiki/Dungeons_%26_Dragons
+[troll]: https://di.ku.dk/Ansatte/?pure=da%2Fpublications%2Ftroll-a-language-for-specifying-dicerolls(84a45ff0-068b-11df-825d-000ea68e967b)%2Fexport.html

exercises/practice/dnd-character/.meta/config.json

@@ -0,0 +1,20 @@
+{
+  "authors": [
+    "mr-sigma",
+    "kotp"
+  ],
+  "files": {
+    "solution": [
+      "dnd_character.rb"
+    ],
+    "test": [
+      "dnd_character_test.rb"
+    ],
+    "example": [
+      ".meta/example.rb"
+    ]
+  },
+  "blurb": "Randomly generate Dungeons & Dragons characters.",
+  "source": "Simon Shine, Erik Schierboom",
+  "source_url": "https://github.com/exercism/problem-specifications/issues/616#issuecomment-437358945"
+}

exercises/practice/dnd-character/.meta/example.rb

@@ -0,0 +1,43 @@
+module Die
+  module_function
+
+  def roll(roll: 4, die: 6, remove_lowest: 1)
+    roll.times.map { rand(1..die) }.sort.pop(roll - remove_lowest).sum
+  end
+end
+
+module Modifiable
+  def modifier(ability_score)
+    ability_score / 2 - 5
+  end
+end
+
+class DndCharacter
+  extend Modifiable
+
+  BASE_HITPOINTS = 10
+
+  private_constant :BASE_HITPOINTS
+
+  private
+  def initialize
+    @strength     = Die.roll
+    @dexterity    = Die.roll
+    @constitution = Die.roll
+    @intelligence = Die.roll
+    @wisdom       = Die.roll
+    @charisma     = Die.roll
+
+    @hitpoints    = BASE_HITPOINTS + self.class.modifier(constitution)
+  end
+
+  public
+
+  attr_reader :strength,
+    :dexterity,
+    :constitution,
+    :intelligence,
+    :wisdom,
+    :charisma,
+    :hitpoints
+end

exercises/practice/dnd-character/.meta/tests.toml

@@ -0,0 +1,72 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[1e9ae1dc-35bd-43ba-aa08-e4b94c20fa37]
+description = "ability modifier -> ability modifier for score 3 is -4"
+
+[cc9bb24e-56b8-4e9e-989d-a0d1a29ebb9c]
+description = "ability modifier -> ability modifier for score 4 is -3"
+
+[5b519fcd-6946-41ee-91fe-34b4f9808326]
+description = "ability modifier -> ability modifier for score 5 is -3"
+
+[dc2913bd-6d7a-402e-b1e2-6d568b1cbe21]
+description = "ability modifier -> ability modifier for score 6 is -2"
+
+[099440f5-0d66-4b1a-8a10-8f3a03cc499f]
+description = "ability modifier -> ability modifier for score 7 is -2"
+
+[cfda6e5c-3489-42f0-b22b-4acb47084df0]
+description = "ability modifier -> ability modifier for score 8 is -1"
+
+[c70f0507-fa7e-4228-8463-858bfbba1754]
+description = "ability modifier -> ability modifier for score 9 is -1"
+
+[6f4e6c88-1cd9-46a0-92b8-db4a99b372f7]
+description = "ability modifier -> ability modifier for score 10 is 0"
+
+[e00d9e5c-63c8-413f-879d-cd9be9697097]
+description = "ability modifier -> ability modifier for score 11 is 0"
+
+[eea06f3c-8de0-45e7-9d9d-b8cab4179715]
+description = "ability modifier -> ability modifier for score 12 is +1"
+
+[9c51f6be-db72-4af7-92ac-b293a02c0dcd]
+description = "ability modifier -> ability modifier for score 13 is +1"
+
+[94053a5d-53b6-4efc-b669-a8b5098f7762]
+description = "ability modifier -> ability modifier for score 14 is +2"
+
+[8c33e7ca-3f9f-4820-8ab3-65f2c9e2f0e2]
+description = "ability modifier -> ability modifier for score 15 is +2"
+
+[c3ec871e-1791-44d0-b3cc-77e5fb4cd33d]
+description = "ability modifier -> ability modifier for score 16 is +3"
+
+[3d053cee-2888-4616-b9fd-602a3b1efff4]
+description = "ability modifier -> ability modifier for score 17 is +3"
+
+[bafd997a-e852-4e56-9f65-14b60261faee]
+description = "ability modifier -> ability modifier for score 18 is +4"
+
+[4f28f19c-2e47-4453-a46a-c0d365259c14]
+description = "random ability is within range"
+
+[385d7e72-864f-4e88-8279-81a7d75b04ad]
+description = "random character is valid"
+
+[2ca77b9b-c099-46c3-a02c-0d0f68ffa0fe]
+description = "each ability is only calculated once"
+include = false
+
+[dca2b2ec-f729-4551-84b9-078876bb4808]
+description = "each ability is only calculated once"
+reimplements = "2ca77b9b-c099-46c3-a02c-0d0f68ffa0fe"

exercises/practice/dnd-character/dnd_character.rb

@@ -0,0 +1,17 @@
+=begin
+Write your code for the 'D&D Character' exercise in this file. Make the tests in
+`dnd_character_test.rb` pass.
+
+To get started with TDD, see the `README.md` file in your
+`ruby/dnd-character` directory.
+=end
+
+class DndCharacter
+  def self.modifier
+    # Your code here
+  end
+
+  def initialize
+    # Your code here
+  end
+end

exercises/practice/dnd-character/dnd_character_test.rb

@@ -0,0 +1,119 @@
+require 'minitest/autorun'
+require_relative 'dnd_character'
+
+module Helpers
+  BASE_HITPOINTS = 10
+
+  def attributes
+    %i[strength dexterity constitution intelligence wisdom charisma]
+  end
+end
+
+class DndCharacterTest < Minitest::Test
+  include Helpers
+
+  def test_modifier_score_3
+    assert_equal(-4, DndCharacter.modifier(3))
+  end
+
+  def test_modifier_score_4
+    assert_equal(-3, DndCharacter.modifier(4))
+  end
+
+  def test_modifier_score_5
+    assert_equal(-3, DndCharacter.modifier(5))
+  end
+
+  def test_modifier_score_6
+    assert_equal(-2, DndCharacter.modifier(6))
+  end
+
+  def test_modifier_score_7
+    assert_equal(-2, DndCharacter.modifier(7))
+  end
+
+  def test_modifier_score_8
+    assert_equal(-1, DndCharacter.modifier(8))
+  end
+
+  def test_modifier_score_9
+    assert_equal(-1, DndCharacter.modifier(9))
+  end
+
+  def test_modifier_score_10
+    assert_equal 0, DndCharacter.modifier(10)
+  end
+
+  def test_modifier_score_11
+    assert_equal 0, DndCharacter.modifier(11)
+  end
+
+  def test_modifier_score_12
+    assert_equal 1, DndCharacter.modifier(12)
+  end
+
+  def test_modifier_score_13
+    assert_equal 1, DndCharacter.modifier(13)
+  end
+
+  def test_modifier_score_14
+    assert_equal 2, DndCharacter.modifier(14)
+  end
+
+  def test_modifier_score_15
+    assert_equal 2, DndCharacter.modifier(15)
+  end
+
+  def test_modifier_score_16
+    assert_equal 3, DndCharacter.modifier(16)
+  end
+
+  def test_modifier_score_17
+    assert_equal 3, DndCharacter.modifier(17)
+  end
+
+  def test_modifier_score_18
+    assert_equal 4, DndCharacter.modifier(18)
+  end
+
+  # rubocop:disable Style/FormatString, Style/RedundantPercentQ
+  def test_random_character_stats
+    100.times do
+      character = DndCharacter.new
+      allowed_range = (3..18)
+      expected_hitpoints = BASE_HITPOINTS +
+                           DndCharacter.modifier(character.constitution)
+      informative_message = %q(The character's %s must be within %s)
+
+      attributes.each do |attribute|
+        assert_includes allowed_range, character.send(attribute),
+          informative_message % [attribute, allowed_range]
+      end
+
+      informative_message = %q(The character's %s must be %s)
+
+      assert_equal expected_hitpoints, character.hitpoints,
+        informative_message % ['hitpoints', expected_hitpoints]
+    end
+  end
+
+  def test_stats_calculated_once
+    informative_message = <<~EXPLAIN
+      The character's %<attribute>s must not change if called more than once.
+      It was %<first>s, is now %<second>s.
+    EXPLAIN
+
+    100.times do
+      character = DndCharacter.new
+
+      (attributes << :hitpoints).each do |attribute|
+        first = character.send(attribute)
+        second = character.send(attribute)
+
+        assert_equal first, second,
+          informative_message % { attribute:, first:, second: }
+      end
+    end
+    # rubocop:enable Style/FormatString, Style/RedundantPercentQ
+  end
+end