Earthdawn Dice

die.rb

class Die
  attr_reader :d, :face, :bonus, :modifier

  def initialize(d)
    parse_d(d)
    @face = roll
    if @d == @face
      @bonus = Die.new(d)
    end
  end

  def result
    bonus = @bonus.nil? ? 0 : @bonus.result
    total = @face - @modifier
    total = 1 if total < 1
    total + bonus
  end

private 

  def parse_d(d)
    case d
    when String
      @d, @modifier = d.split('-').map{|i| i.to_i}
    else
      @d = d
      @modifier = 0
    end
  end

  def roll
    1 + rand(d)
  end

end

die_test.rb

require 'test_helper'

class DieTest < ActiveSupport::TestCase

  should 'roll a bonus die' do 
    Die.any_instance.stubs(:roll).returns(6, 4)
    die = Die.new(6)

    assert die.result == 10
  end
  
  should 'roll multiple bonus dice' do 
    Die.any_instance.stubs(:roll).returns(6, 6, 6, 4)
    die = Die.new(6)

    assert die.result == 22
  end

  should 'accept modifier' do
    Die.any_instance.stubs(:roll).returns(5)
    die = Die.new("6-3")
    assert die.modifier == 3
    assert die.result == 2
  end

  should 'not be less then 1' do
    Die.any_instance.stubs(:roll).returns(1)
    die = Die.new("6-3")
    assert die.modifier == 3
    assert die.result > 0
  end

  should 'roll bonus on modified die' do
    Die.any_instance.stubs(:roll).returns(6, 3)
    die = Die.new('6-3')

    assert die.result == 4

  end
end

roll.rb

class Roll
  include ActiveModel::AttributeMethods
  STEPS = {
    1 => ['6-3'],
    2 => ['6-2'],
    3 => ['6-1'],
    4 => [6],
    5 => [8],
    6 => [10],
    7 => [12],
    8 => [6, 6],
    9 => [8, 6]
  }
  attr_accessor :result, :step, :dice

  def initialize(options = {})
    @step = options[:step] || 4
    @dice = STEPS[@step].map{|d| Die.new(d)}
    @result = @dice.inject(0){|sum, n| sum + n.result}
  end

end

roll_test.rb

require 'test_helper'

class RollTest < ActiveSupport::TestCase

  test 'testing' do
    assert true
  end

  should 'have a result' do
    roll = Roll.new()
    assert_not_nil roll.result
  end

  should 'accept a step number on create' do
    roll = Roll.new(:step => 4)
    assert roll.step = 4
  end

  should 'roll the right dice for several step numbers' do
    roll = Roll.new(:step => 1)
    assert roll.dice.first.d == 6, 'sixer for step 1'
    assert roll.dice.first.modifier == 3, 'minus 3 for step 1'

    roll = Roll.new(:step => 4)
    assert roll.dice.first.d == 6, 'sixer for step 4'
    
    roll = Roll.new(:step => 5)
    assert roll.dice.first.d == 8, 'eight-sided for step 5'

    roll = Roll.new(:step => 8)
    assert roll.dice.map{|d| d.d} == [6,6], 'two sixes for step 8'
  end

end