tic_tac_toe.rb

# Tic Tac Toe
# 1. Come up with requirments/specification, whihc will determine the scope.
# 2. Application logic; sequence of steps
# 3. Translation of those steps into code
# 4. Run code to verify logic
#

# Psuedo Code
# draw a board
#
# assing player to "X"
# assign computer to "O"
#
# loop until a winner or all squares are taken
#   player1 picks an empty square
#   check for winner
#   player2 picks an empty square
#   check for winner
#
# if there's a winner
#   show the winner
# or else
#   it's a tie

def initialize_board
  board = {}
  (1..9).each { |position| board[position] = ' ' }
  board
end

def draw_board(board)
  system 'clear'
  puts " #{board[1]} | #{board[2]} | #{board[3]} "
  puts '-----------'
  puts " #{board[4]} | #{board[5]} | #{board[6]} "
  puts '-----------'
  puts " #{board[7]} | #{board[8]} | #{board[9]} "
end

def empty_positions(board)
  board.keys.select { |position| board[position] == ' ' }
end

def player_picks_square(board)
  begin
    puts 'Pick a square:(1-9):'
    position = gets.chomp.to_i
  end until empty_positions(board).include?(position)
  board[position] = 'X'
end

def computer_picks_square(board)
  defend_this_square = nil
  position = nil
  WINNING_LINES.each do |l|
    defend_this_square = two_in_a_row({l[0] => board[l[0]], l[1] => board[l[1]], l[2] => board[l[2]]} )
    if defend_this_square
      position = defend_this_square
      break
    end
  end
  position = empty_positions(board).sample unless defend_this_square
  board[position] = 'O'
end

def check_winner(board)
  WINNING_LINES.each do |line|
    return 'Player' if board.values_at(*line).count('X') == 3
    return 'Computer' if board.values_at(*line).count('O') == 3
  end
  nil
end

def two_in_a_row(board)
  return false unless board.values.count('X') == 2
  empty_positions(board).first
end

def announce_winner(winner)
  puts "#{winner} won!"
end

def nine_positions_are_filled?(board)
  empty_positions(board).empty?
end

WINNING_LINES = [[1, 2, 3], [4, 5, 6], [7, 8, 9], [1, 4, 7], [2, 5, 8], [3, 6, 9], [1, 5, 9], [3, 5, 7]]

board = initialize_board
draw_board(board)
begin
  player_picks_square(board)
  two_in_a_row(board)
  draw_board(board)
  winner = check_winner(board)
  if winner == 'Player'
    next
  end
  computer_picks_square(board)
  draw_board(board)
  winner = check_winner(board)
end until winner || nine_positions_are_filled?(board)

if winner
  announce_winner(winner)
else
  puts "It's a tie!"
end