tic tac toe in ruby - refactoring part 3

require 'player'
require 'board'
require 'ui'

class MinMaxPlayer < Player

  def initialize(piece)
    super(piece)
  end

  def get_opponent(piece)
    return piece === 'O' ? 'X' : 'O'
  end

  def evaluate_score(board, piece)
    opponent = get_opponent(piece)
    case board.winner
    when piece
      return 1
    when opponent
      return -1
    else
      return 0
    end
  end

  def get_best_move(board, piece, depth)
    if board.game_over?
      return evaluate_score(board, piece)
    else
      best_score = -999
      opponent = get_opponent(piece)
      empty_squares = board.get_empty_squares
      empty_squares.each do |s|
        temp_board = Board.new(board.to_a)
        temp_board.move(s, piece)
        score = -get_best_move(temp_board, opponent, depth + 1)
        if score > best_score
          best_score = score
          @best_move = s if depth == 1
        end
      end
      return best_score
    end
  end

  def make_move
    @ui.display_message("Player '#{@piece}' makes a move\n")
    if @board.get_empty_squares.size == @board.size
      return rand(@board.size)
    end
    get_best_move(@board, @piece, 1)
    return @best_move
  end
end

require File.expand_path(File.dirname(__FILE__)) + "/spec_helper"
require 'min_max_player.rb'
require 'board'
require 'ui'
require 'stringio'

describe MinMaxPlayer do
  before(:each) do
    @x = 'X'
    @o = 'O'
    @b = ' '
    @ui = UI.new(StringIO.new, StringIO.new)
    @min_max = MinMaxPlayer.new(@x)
    @min_max.ui = @ui
    @board = Board.new
    @min_max.board = @board
  end

  it "should inherit from Player" do
    MinMaxPlayer.ancestors.include?(Player).should == true
  end

  it "should return correct opponent" do
    @min_max.get_opponent(@o).should == @x
    @min_max.get_opponent(@x).should == @o
  end

  it "should return 1 if Max is winner" do
    @board.move(0, @x)
    @board.move(1, @x)
    @board.move(2, @x)
    @min_max.evaluate_score(@board, @x).should == 1
  end

  it "should return -1 if Min is winner" do
    @board.move(0, @o)
    @board.move(1, @o)
    @board.move(2, @o)
    @min_max.evaluate_score(@board, @x).should == -1
  end

  it "should return -1 if Max is winner (from Min POV)" do
    @board.move(0, @x)
    @board.move(1, @x)
    @board.move(2, @x)
    @min_max.evaluate_score(@board, @o).should == -1
  end

  it "should return 1 if Min is winner (from Min POV)" do
    @board.move(0, @o)
    @board.move(1, @o)
    @board.move(2, @o)
    @min_max.evaluate_score(@board, @o).should == 1
  end

  it "should return 0 if no one is winner" do
    board = Board.new([@x, @x, @o, @o, @x, @x, @x, @o, @o])
    @min_max.evaluate_score(board, @x).should == 0
  end

  it "should make winning move" do
    @board.move(0, @x)
    @board.move(1, @o)
    @board.move(2, @x)
    @board.move(3, @o)
    @board.move(4, @x)
    @board.move(5, @o)
    @board.move(6, @o)

    @min_max.make_move.should == 8
  end

  it "should make winning move 2" do
    @board.move(0, @x)
    @board.move(1, @o)
    @board.move(2, @x)
    @board.move(3, @o)

    @min_max.make_move.should == 4
  end

  it "should make winning move 3" do
    @board.move(0, @o)
    @board.move(1, @x)
    @board.move(3, @o)
    @board.move(4, @o)
    @board.move(6, @x)
    @board.move(7, @x)

    @min_max.make_move.should == 8
  end

  it "should make blocking move, scenario 1" do
    @board.move(0, @x)
    @board.move(3, @o)
    @board.move(4, @o)
    @min_max.make_move.should == 5
  end

  it "should make winning move, scenario 3" do
    @board.move(0, @x)
    @board.move(1, @o)
    @board.move(2, @x)
    @board.move(3, @o)
    @board.move(5, @o)
    @board.move(7, @x)

    @min_max.make_move.should == 4
  end

  it "should not make secret losing move" do
    @board.move(0, @x)
    @board.move(4, @o)
    @board.move(8, @o)

    @min_max.make_move.should == 2
  end
end