tictactoe.rb

class TicTacToe
  PLAYERS = 2
  MARKERS = "×○"
  COLOR_NUM = 7

  def initialize
    @game = Array.new(9)
    @winner = nil
  end

  def play
    player = 0

    while @winner.nil?
      turn player
      player = (player + 1) % PLAYERS
    end

    show_grid
    if @winner
      puts "Congratulation, player #{@winner + 1}: you won!"
    else
      puts "No winner this time."
    end
  end

  def turn(player)
    show_grid

    place_marker player
    check_win
  end

  def place_marker(player)
    puts "Player #{player + 1} (#{MARKERS[player]}) is on!"

    sel = loop do
      sel = get_input
      break sel if is_valid?(sel)

      $stderr.puts "This cell is either full or out of the map. Try another one."
    end

    mark_on_grid player, sel
  end

  def show_grid
    rows = @game.map.with_index do |player, n|
      if player
        "\e[3#{player + 1}m#{MARKERS[player]}\e[0m"
      else
        "\e[3#{COLOR_NUM}m#{n + 1}\e[0m"
      end
    end.each_slice(3).map { |e| ([nil] + e + ["\n"]).join '|' }
    puts ([nil] + rows + ["\n"]).join("+-+-+-+\n")
  end

  def mark_on_grid(player, sel)
    @game[sel - 1] = player
  end

  def get_input
    loop do
      begin
        $stdout.write "Your play: "
        $stdout.flush

        break Integer(gets.strip)
      rescue ArgumentError
        $stderr.puts "Invalid input."
      end
    end
  end

  def is_valid?(choice)
    choice.between?(1, 9) && @game[choice - 1].nil?
  end

  def check_win
    row_checker = lambda do |row|
      if row.each_cons(2).all? { |a, b| a == b } && row.first
        @winner = row.first
        return
      end
    end

    # Horizontal
    @game.each_slice(3, &row_checker)

    # Vertical
    @game.each_slice(3).to_a.transpose.each(&row_checker)

    # Diagonal
    [[0,4,8],[2,4,6]].each do |e|
      e.map { |i| @game[i] }.tap(&row_checker)
    end

    # All full
    if @game.all?(&:itself)
      @winner = false
    end
  end
end

TicTacToe.new.tap do |game|
  game.play
end