tictactoe/bot.rb

class Bot

  attr_reader :best_choice, :val
  
  def initialize board, piece
    @val = piece
    @piece = piece
    @opponent = switch piece
  end

  def move board
    minmax board, @piece
    board.set @piece, @best_choice
  end


  def minmax board, cur_player
    return score(board) if game_done?(board)
    
    scores = {}
    
    board.get_free.each do |space|
      # dup and clone only create a shallow clone, so it doesn't clone the array inside the board object.
      board.set cur_player, space

      scores[space] = minmax(board, switch(cur_player))

      board.remove space
    end

    @best_choice, best_score = best_choice cur_player, scores
    best_score
  end

  def switch cur
    cur == " X " ? " O " : " X "
  end

  def game_done? board
    board.any_winner? || board.is_full?
  end
  
  def best_choice piece, scores
    if piece == @piece then
      #p scores
      scores.max_by { |_k, v| v}
    else
      scores.min_by { |_k, v| v}
    end
  end
  
  def score board

    if board.is_winner? @piece 
      return 10
    elsif board.is_winner? @opponent
      return -10
    end
    0
  end
  
end