### Tic Tac Toe ###

# instructions
# determine who goes first
# create board
# display board
# while no one has one and it's not a tie:
## if its human's turn
### get human's move
### update the board with the move
## otherwise
### calculate the computer's move
### update the board with the move
## display the board
## switch turns
# congratulate the winner or declare a tie

# Global Constants

X = "X"
O = "O"
EMPTY = " "
TIE = "TIE"
SQUARES = (1, 2, 3, 4, 5, 6, 7, 8, 9)

def displayInstruct():
    """ Display game instructions. """
    print(
        """
    Welcome to the greatest intellectual challenge of all time: Tic-Tac-Toe.
    This will be a showdown between your human brain and my silicon processor.

    You will make your move known by entering a number, 1 - 9.  The number
    will correspond to the board position as illustrated:

             1 | 2 | 3
             ---------
             4 | 5 | 6
             ---------
             7 | 8 | 9

    Prepare yourself, human.  The ultimate battle is about to begin.  \n
    """
        )

def askYesNo(question):
    """Ask a yes or no question."""
    response = None
    while response not in ("y", "n"):
        response = input(question).lower()
        response = response.rstrip("\r\n")
    return response

def askNumber(question, low, high):
    """ Ask for a number within a range."""
    response = None
    while response not in range(low, high):
        response = input(question)
        response = response.rstrip("\r\n")
        response = int(response)
    return response

def pieces():
    """Determine if the player or computer goes first. """
    go_first = askYesNo("Do you require the first move?  (y/n): ")
    if go_first == "y":
        print("\nThen take the first move.  You will need it.")
        human = X
        computer = O

    else:
        print("\nYour bravery will be your undoing... I will go first." )
        computer = X
        human = O

    return computer, human

def newBoard():
    """Create new game board."""
    board = []
    for i in SQUARES:
        board.append(EMPTY)
    return board

def displayBoard(board):
    """Display game board on screen."""
    print("\n\t", board[0], "|", board[1], "|", board[2] )
    print("\t", "--------- ")
    print("\t", board[3], "|", board[4], "|", board[5] )
    print("\t", "--------- ")
    print("\t", board[6], "|", board[7], "|", board[8] )

def legalMoves(board):
    """Create a list of legal moves."""
    moves = []
    for i in SQUARES:
        if board[i] == EMPTY:
            moves.append(i)
    return moves

def winner(board):
    """ Determine the game winner. """
    WAYS_TO_WIN = ((1, 2, 3),
                   (4, 5, 6),
                   (7, 8, 9),
                   (1, 4, 7),
                   (2, 5, 8),
                   (3, 6, 9),
                   (1, 5, 9),
                   (7, 5, 3))

    for row in WAYS_TO_WIN:
        if board[row[0]] == board[row[1]] == board[row[2]] != EMPTY:
            winner = board[i[0]]
            return winner
    if EMPTY not in board:
        return TIE
    return None

def humanMove(board, human):
    """Get human's move."""
    legal = legalMoves(board)
    move = None
    while move not in legal:
        move = askNumber("Where will you move? (1 - 9): ", 1, 10)
        if move not in legal:
            print("\nThat square is already occupied, foolish human.  Choose another.\n")
    print("Fine..." )
    return move

def computerMove(board, computer, human):
    "make computer move."""
    #making a copy to work with since function will be changing list

    lboard = board[:]

    BEST_MOVES = (5, 7, 9, 1, 3, 4, 8, 6, 2)

    print("I shall take square number", end=" ")
    # if computer can win, take that move:
    for move in legalMoves(board):
        lboard[move] = computer
        if winner(board) == computer:
            print(move)
            return move
        #done checking move, undo it:
        lboard[move] = EMPTY

    # if human can win, block the move:
    for move in legalMoves(board):
        lboard[move] = human
        if winner(board) == human:
            print(move)
            return move
    #done checking move, undo it:
        lboard[move] = EMPTY

    #since no one can win, pick best open square:
    for move in BEST_MOVES:
        if move in legalMoves(board):
            print(move)
            return move

def nextTurn(turn):
    """Switch turns."""
    if turn == X:
        return O
    else:
        return X

def congratWinner(the_winner, computer, human):
    if the_winner != TIE:
        print(the_winner, "won!\n")
    else:
        print("It's a tie!\n")

    if the_winner == computer:
        print("As I predicted, human, I am triumpant once more.  \n" \
              "Proff that computers are superior to humans in all regards." )

    elif the_winner == human:
        print("No, no!  It cannot be!  Somehow you tricked me, human.  \n" \
              "But never again!  I, the computer, so swear it!")

    elif the_winner == TIE:
        print("You were most lucky, human, and somehow managed to tie me.  \n" \
              "Celebrate today, for this is the best you will ever achieve.")

def playAgain():
    replay = askYesNo("\n\nWould you like to play again?  (y/n): ")
    if replay == "y":
        return True
    else:
        return False

def main():
    displayInstruct()
    computer, human = pieces()
    turn = X
    board = newBoard()
    displayBoard(board)

    while not winner(board):
        if turn == human:
            move = humanMove(board, human)
            board[move] = human
        else:
            move = computerMove(board, computer, human)
            board[move] = computer
        displayBoard(board)
        turn = nextTurn(turn)

    the_winner = winner(board)
    congratWinner(the_winner, computer, human)

while True:
    main()
    playAgain()

## The Error:
##Traceback (most recent call last):
##  File "C:\Python32\tic-tactoe.py", line 217, in <module>
##    main()
##  File "C:\Python32\tic-tactoe.py", line 203, in main
##    while not winner(board):
##  File "C:\Python32\tic-tactoe.py", line 113, in winner
##    if board[row[0]] == board[row[1]] == board[row[2]] != EMPTY:
##IndexError: list index out of range