class TicTacToe

# File lib/tic_tac_toe.rb, line 17
def initialize
  @fields = Array.new(9).fill(' ')
  @position = 0
  @player = PLAYERS.first
end

# File lib/tic_tac_toe.rb, line 100
def self.array_indexes(array, find)
  indexes = []
  array.each_with_index{|item,i| indexes << i if find == item }
  indexes
end

# File lib/tic_tac_toe.rb, line 44
def ai_move
  return unless position = ai_select_position
  @position = position
  set
end

# File lib/tic_tac_toe.rb, line 23
def board
  index = -1
  BOARD.gsub(" X ") do
    index += 1
    field = @fields[index]
    @position == index ? "[#{field}]" : " #{field} "
  end
end

# File lib/tic_tac_toe.rb, line 50
def draw?
  @fields.index(' ') == nil
end

# File lib/tic_tac_toe.rb, line 32
def move(x,y)
  x = (@position + x) % 3
  y = ((@position / 3) + y) % 3
  @position = x + (y * 3)
end

# File lib/tic_tac_toe.rb, line 38
def set
  return if @fields[@position] != ' '
  @fields[@position] = @player
  @player = next_player
end

# File lib/tic_tac_toe.rb, line 54
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

# File lib/tic_tac_toe.rb, line 71
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

# File lib/tic_tac_toe.rb, line 83
def can_by_taking?(position, player)
  taking(position, player) do
    winner = self.winner
    winner == player
  end
end

# File lib/tic_tac_toe.rb, line 106
def next_player
  current_index = PLAYERS.index(@player)
  next_index = (current_index + 1) % PLAYERS.size
  PLAYERS[next_index]
end

# File lib/tic_tac_toe.rb, line 90
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