import random

def main():

    def isDraw(board):
        for i in board:
            if i == ' ':
                return False
        return True

    def printBoard(board):
        print("""
    {} | {} | {}
---+---+---
    {} | {} | {}
---+---+---
    {} | {} | {}
""".format(board[0],board[1],board[2],
    board[3],board[4],board[5],
    board[6],board[7],board[8]))
    
    def isWin(player,board):
        row1 = ((board[0] == player) and (board[1] == player) and (board[2] == player))
        row2 = ((board[3] == player) and (board[4] == player) and (board[5] == player))
        row3 = ((board[6] == player) and (board[7] == player) and (board[8] == player))
        column1 = ((board[0] == player) and (board[3] == player) and (board[6] == player))
        column2 = ((board[1] == player) and (board[4] == player) and (board[7] == player))
        column3 = ((board[2] == player) and (board[5] == player) and (board[8] == player))
        diaLeft = ((board[0] == player) and (board[4] == player) and (board[8] == player))
        diaRight = ((board[2] == player) and (board[4] == player) and (board[6] == player))
        return (row1 or row2 or row3 or column1 or column2 or column3 or diaLeft or diaRight)

    def playTurn(playMark,board):
        accept = False
        while not accept:
            pos = input("Enter position to place {}: ".format(playMark))
            if pos.isnumeric():
                if len(pos) == 1:
                    pos = int(pos)
                    if pos in range(1,10):
                        valid = ((7,8,9,4,5,6,1,2,3),(0,1,2,3,4,5,6,7,8))
                        pos = valid[1][valid[0].index(pos)]
                        if board[pos] == ' ':
                            accept = True
                            return pos
                        else:
                            print("The position is already filled!\n")
                    else:
                        print("Invalid position!\n")
                else:
                    print("Enter only one digit value!\n")
            else:
                print("Enter only numerical value!\n")


    def comTurn(playMark,comMark,board):

        for i in range(8):
            copy = board[:]
            if copy[i] == ' ':
                copy[i] = comMark
                if isWin(comMark,copy):
                    return i

        for i in range(8):
            copy = board[:]
            if copy[i] == ' ':
                copy[i] = playMark
                if isWin(playMark,copy):
                    return i
        
        corners = (0,2,6,8)
        edges = (1,3,5,7)
        possibleCorners = [i for i in range(len(corners)) if board[i] == ' ']
        possibleEdges = [i for i in range(len(edges)) if board[i] == ' ']
        
        if len(possibleCorners) != 0:
            return random.choice(possibleCorners)
        
        if board[4] == ' ':
            return 4
        
        if len(possibleEdges) != 0:
            return random.choice(possibleEdges)
    
    
    print("""
The arrangement is as follows:

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

Tip: If a number pad is present, use it!
""")
    choice = False
    while not choice:
        first = input("Do you want to go first (y/n)?: ").lower()
        if first in ('y',"yes",''):
            playMark = 'X'
            comMark = 'O'
            turn = 'p'
            choice = True
        elif first in ('n',"no"):
            playMark = 'O'
            comMark = 'X'
            turn = 'c'
            choice = True

    while True:
        board = [' '] * 9
        game = True
        while game:
            printBoard(board)
            if turn == 'p':
                pos = playTurn(playMark,board)
                board[pos] = playMark
                if isWin(playMark,board):
                    printBoard(board)
                    print("You WIN!")
                    game = False
                else:
                    if isDraw(board):
                        printBoard(board)
                        print("It's a DRAW!")
                        game = False
                    else:
                        turn = 'c'

            else:
                pos = comTurn(playMark,comMark,board)
                board[pos] = comMark
                if isWin(comMark,board):
                    printBoard(board)
                    print("The computer wins!")
                    game = False
                else:
                    if isDraw(board):
                        printBoard(board)
                        print("It's a DRAW!")
                        game = False
                    else:
                        turn = 'p'

        continuing = input("Want to play again (y/n)?: ")
        if continuing in ('n',"no"):
            break


main()