import random

def tic_tac_toe(request):

    request_json = request.get_json()

    try:

        board = request_json['board']

    except:

        return 'Did not include board!!!'

    if not isinstance(board, list):

        return "Invalid board. Must be a list"

    if len(board) != 3:

        return "Invalid board. Outer array is not of length 3"

    move = None

    for i, row in enumerate(board):

        if not isinstance(row, list):

            return f"Invalid board. Row {i} is not a list"

        if len(row) != 3:

            return f"Invalid board. Row {i} is not length 3"

        for j, elem in enumerate(row):

            if elem == '':

                if not move or random.randrange(100) < 50:

                    move = [i,j]

            if elem not in ['X','O','']:

                return f'Invalid board. Elem [{i}][{j}] not valid.'

    if not move:

        return "Invalid board. Cat's game board"

    for i in range(len(board)):

        if board[i].count('X') == len(board):

            return 'You already won!'

        if board[i].count('O') == len(board):

            return 'I already won!'

        if len( {board[0][i], board[1][i], board[2][i]} ) == 1:

            if board[0][i] == 'X': 

                return 'You already won!'

            if board[0][i] == 'O':

                return 'I already won!'

        # Check diagonals

        if 1 in [

           len( {board[0][0], board[1][1], board[2][2]} ),

           len( {board[2][0], board[1][1], board[0][2]} )]:

            if board[1][1] == 'X':

                return 'You already won!'

            if board[1][1] == 'O':

                return 'I already won!'

    board[move[0]][move[1]] = 'O'

    return f'{board}'