require 'tic_tac_toe/version'

class TicTacToe
  BOARD = <<BOARD
-------------
| X | X | X |
-------------
| X | X | X |
-------------
| X | X | X |
-------------
BOARD
  PLAYERS = ['X','O']

  attr_reader :position, :player

  def initialize
    @fields = Array.new(9).fill(' ')
    @position = 0
    @player = PLAYERS.first
  end

  def board
    index = -1
    BOARD.gsub(" X ") do
      index += 1
      field = @fields[index]
      @position == index ? "[#{field}]" : " #{field} "
    end
  end

  def move(x,y)
    x = (@position + x) % 3
    y = ((@position / 3) + y) % 3
    @position = x + (y * 3)
  end

  def set
    return if @fields[@position] != ' '
    @fields[@position] = @player
    @player = next_player
  end

  def ai_move
    return unless position = ai_select_position
    @position = position
    set
  end

  def draw?
    @fields.index(' ') == nil
  end

  def winner
    [
      [0,1,2],[3,4,5],[6,7,8],  # vertical
      [0,3,6],[1,4,7],[2,5,8],  # horizontal
      [0,4,8],[2,4,6]           # diagonal
    ].each do |pattern|
      players = pattern.map{|i| @fields[i] }.uniq
      next if players.size != 1
      winner = players.first
      next if winner == ' '
      return winner
    end
    nil
  end

  private

  def ai_select_position
    return if winner or draw?
    free_positions = self.class.array_indexes(@fields, ' ')

    # how can i win ?
    free_positions.detect{|position| can_by_taking?(position, @player) } or
    # how can i prevent opponent from winning ?
    free_positions.detect{|position| can_by_taking?(position, next_player) } or
    # guess
    free_positions.sort_by{rand}.first
  end

  def can_by_taking?(position, player)
    taking(position, player) do
      winner = self.winner
      winner == player
    end
  end

  def taking(position, player)
    old_player, @player = @player, player
    old_field = @fields[position]
    @fields[position] = @player
    yield
  ensure
    @fields[position] = old_field
    @player = old_player
  end

  def self.array_indexes(array, find)
    indexes = []
    array.each_with_index{|item,i| indexes << i if find == item }
    indexes
  end

  def next_player
    current_index = PLAYERS.index(@player)
    next_index = (current_index + 1) % PLAYERS.size
    PLAYERS[next_index]
  end
end