# tic tac toe

import random

def drawBoard(board):
	# prints out the tic tac toe board from the list taken in
	# board is a list of 9 strings representing the board
	'''
	 0 | 1 | 2
	---+---+---
	 3 | 4 | 5
	---+---+---
	 6 | 7 | 8
	'''
	print(f' {board[0]} | {board[1]} | {board[2]}')
	print('---+---+---')
	print(f' {board[3]} | {board[4]} | {board[5]}')
	print('---+---+---')
	print(f' {board[6]} | {board[7]} | {board[8]}')


def inputPlayerLetter():
	# Lets the player choose X's or O's
	# Returns a list with the player's letter first and 
	# computer letter second: [X, O] or [O, X]
	letter = ''
	while not (letter == 'X' or letter == 'O'):
		print("Do you want to be X's or O's?")
		letter = input().upper()
	
	if letter == 'X':
		return ['X', 'O'] # player is X's, computer is O's
	else:
		return ['O', 'X'] # player is O's, computer is X's


def whoGoesFirst():
	# randomly choose which player goes first
	if random.randint(0,1) == 0:
		return 'computer'
	else:
		return 'player'


def makeMove(board, letter, move):
	board[move] = letter


def isWinner(board, letter):
	# Given the board and the letter to check, see if that
	# player has won

		   
	return (board[0] == letter and board[1] == letter and board[2] == letter) or (board[3] == letter and board[4] == letter and board[5] == letter) or (board[6] == letter and board[7] == letter and board[8] == letter) or (board[0] == letter and board[3] == letter and board[6] == letter) or (board[1] == letter and board[4] == letter and board[7] == letter) or (board[2] == letter and board[5] == letter and board[8] == letter) or (board[0] == letter and board[4] == letter and board[8] == letter) or (board[2] == letter and board[4] == letter and board[6] == letter) # diagonal check


def getBoardCopy(board):
	# make a copy of the board list and return it
	boardCopy = []
	for i in board:
		boardCopy.append(i)
	return boardCopy


def isSpaceFree(board, move):
	# returns True if the move parameter space on the board is empty
	return board[move] == ' '


def getPlayerMove(board):
	# let the player enter their move
	move = ' '
	# player has to choose 0 - 9 and it has to be a free space
	while True:
		print('What is your next move? (0-8)')
		move = input()
		if move.isdigit() and int(move) in range(9):
			move = int(move)
			if isSpaceFree(board, move):
				return move
			else:
				print('Spot already taken!')
		else:
			print('Invalid input! Enter a number 0-8')
	# while move not in '0 1 2 3 4 5 6 7 8'.split() or not isSpaceFree(board, int(move)):
	# 	if move.isdigit() and int(move) in list(range(9)):
	# 		if not isSpaceFree(board, int(move)):
	# 			print('Spot already taken!')
	# 	print('What is your next move? (0-8)')
	# 	move = input()
	# return int(move)


def chooseRandomMoveFromList(board, movesList):
	# returns a random, valid move from the list passed in
	# returns None if there are no valid moves
	possibleMoves = []

	for move in movesList:
		if isSpaceFree(board, move):
			possibleMoves.append(move)

	if len(possibleMoves) != 0:
		return random.choice(possibleMoves)
	else:
		return None


def getComputerMove(board, computerLetter):
	# given a board and the computer's letter, determine
	# the best move for the computer to make, and make it
	if computerLetter == 'X':
		playerLetter = 'O'
	else:
		playerLetter = 'X'

	# Computer check for winning move first
	for spot in range(9):
		boardCopy = getBoardCopy(board)
		if isSpaceFree(boardCopy, spot):
			makeMove(boardCopy, computerLetter, spot)
			if isWinner(boardCopy, computerLetter):
				return spot

	# if no winning moves, check if we need to block
	for spot in range(9):
		boardCopy = getBoardCopy(board)
		if isSpaceFree(boardCopy, spot):
			makeMove(boardCopy, playerLetter, spot)
			if isWinner(boardCopy, playerLetter):
				return spot

	# if no need to block player, choose a corner (0, 2, 6, or 8)
	move = chooseRandomMoveFromList(board, [0, 2, 6, 8])
	if move != None:
		return move

	# if no corners, take the center (4)
	if isSpaceFree(4): 
		return 4

	# if center is not free, choose a side spot (1, 5, 7, or 9)
	return chooseRandomMoveFromList(board, [1, 5, 7, 3])


def isBoardFull(board):
	# if every space on the board is taken, True. Otherwise false
	for spot in board:
		if spot == ' ':
			return False

	# no blank spots, board is full
	return True


print('Welcome to Tic-Tac-Toe!')
print('The board has spots 0 through 8. When you pick ' \
	'your spot, use the key to make sure you know where ' \
	'you are going.')
print('''KEY:
 0 | 1 | 2
---+---+---
 3 | 4 | 5
---+---+---
 6 | 7 | 8
	''')
while True:
	# Reset the board
	board = [' '] * 9
	playerLetter, computerLetter = inputPlayerLetter()
	turn = whoGoesFirst()
	print('The ' + turn + ' will go first.')

	gameIsPlaying = True

	while gameIsPlaying:
		if turn == 'player':
			# player turn logic
			drawBoard(board)
			move = getPlayerMove(board)
			makeMove(board, playerLetter, move)

			if isWinner(board, playerLetter):
				drawBoard(board)
				print('You won!')
				gameIsPlaying = False
			elif isBoardFull(board):
					drawBoard(board)
					print('The game is a tie!')
					break
			else:
				turn = 'computer'
		else:
			# computer turn logic
			move = getComputerMove(board, computerLetter)
			makeMove(board, computerLetter, move)

			if isWinner(board, computerLetter):
				drawBoard(board)
				print('You lost!')
				gameIsPlaying = False
			elif isBoardFull(board):
					drawBoard(board)
					print('The game is a tie!')
					break
			else:
				turn = 'player'

	print('Do you want to play again? (yes or no)')
	if not input().lower().startswith('y'):
		break