two_player_game.rb

module Constants
  InitialLives = 3
  InitialScore = 0
  InitialRecord = 0
  RandUpper = 20
  RandLower = 1
end

class Question
  include Constants

  attr_accessor :first_num, :second_num

  def to_s
    "What's #{first_num} + #{second_num}?"
  end

  def initialize
    self.first_num = rand_num
    self.second_num = rand_num
  end

  def sum
    first_num + second_num
  end

  def correct_guess?(guess)
    guess == sum
  end

  private

  def rand_num
    rand(RandLower..RandUpper)
  end
end

class Player
  include Constants

  attr_accessor :lives, :score, :name

  def no_more_lives?
    lives <= 0
  end

  def initialize(name)
    @name = name
    @lives = InitialLives
    @score = InitialScore
  end

  def status
    "Player #{name} has #{lives} lives and #{score} points"
  end

  def to_s
    name
  end
end

class Game
  include Constants

  attr_reader :players

  def initialize(players)
    @players = players
    @turn = 0
  end

  def current_player
    @players[@turn % 2]
  end

  def next_turn!
    @turn += 1
  end

  def over?
    @players.any? { |p| p.no_more_lives? }
  end

  class << self
    def input(prompt)
      print "#{prompt} "
      gets.chomp
    end

    def setup_player(number)
      Player.new(input("Player #{number}, please enter your name:"))
    end

    def play
      game = Game.new([1, 2].map{ |n| setup_player(n) })
      until game.over?
        question = Question.new
        puts "Player #{game.current_player}'s turn"
        answer = input("Player #{game.current_player}, #{question}")
        if question.correct_guess?(answer.to_i)
          game.current_player.score += 1
          puts "Correct!"
        else
          game.current_player.lives -= 1
          puts "Wrong!"
        end
        puts game.current_player.status
        game.next_turn!
      end
      puts "Game over!"
      game.players.each do |player|
        puts "Player #{player} has #{player.lives} lives and #{player.score} points"
      end
    end
  end
end