/* Copyright (C) 2014 by Alexandru Cojocaru */

/* This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>. */


#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <error.h>


enum {MX = 1, MO = 2, Draw = 3};


static bool
win_p (int b[3][3], int mark)
{
	for (int i = 0; i < 3; ++i) {
		if (b[i][0] == mark &&
		    b[i][1] == mark &&
		    b[i][2] == mark)
			return 1;

		if (b[0][i] == mark &&
		    b[1][i] == mark &&
		    b[2][i] == mark)
			return 1;
	}

	if (b[0][0] == mark && b[1][1] == mark && b[2][2] == mark)
		return 1;

	if (b[2][0] == mark && b[1][1] == mark && b[0][2] == mark)
		return 1;

	return 0;
}

static bool
draw_p (int b[3][3])
{
	for (int i = 0; i < 3; ++i)
		for (int j = 0; j < 3; ++j)
			if (b[i][j] == 0)
				return 0;

	return ! (win_p (b, MX) || win_p (b, MO));
}

static bool
gameover_p (int b[3][3])
{
	return win_p (b, MX) || win_p (b, MO) || draw_p (b);
}

static int
negamax (int b[3][3], int mark, int move)
{
	int opponentmark;
	if (mark == MX)
		opponentmark = MO;
	else
		opponentmark = MX;


	if (win_p (b, mark))
		return 1;
	else if (win_p (b, opponentmark))
		return -1;
	else if (draw_p (b))
		return 0;


	int max, maxi, maxj;
	max = -2;
	for (int i = 0; i < 3; ++i) {
		for (int j = 0; j < 3; ++j) {
			if (b[i][j] == 0) {
				b[i][j] = mark;
				int m = -negamax (b, opponentmark, 0);
				if (m > max) {
					max = m;
					maxi = i;
					maxj = j;
				}
				b[i][j] = 0;
			}
		}
	}


	if (move) {
		printf ("AI marks `%d'\n", maxj+1 + (maxi)*3);
		b[maxi][maxj] = mark;
	}

	return max;
}


static char
tochar (int mark)
{
	if (mark == MX)
		return 'X';
	else if (mark == MO)
		return 'O';
	else
		return ' ';
}

static void
printb (int b[3][3])
{
	for (int i = 0; i < 3; ++i) {
		printf ("|");
		for (int j = 0; j < 3; ++j)
			printf (" %c |", tochar (b[i][j]));
		printf ("\n");
		if (i != 2)
			for (int j = 0; j < 13; ++j)
				printf ("-");
		printf ("\n");
	}
}

static void
usermove (int b[3][3], int mark)
{
	int n;

	printf ("Where to put the mark (1-9): ");

	scanf ("%d", &n);

	if (n < 1 || n > 9) {
		error (0, 0, "number must be between `0' and `9' (was given: %d)", n);
		usermove (b, mark);
		return;
	}

	--n;

	if (b[n/3][n%3]) {
		error (0, 0, "cell not empty");
		usermove (b, mark);
		return;
	}

	b[n/3][n%3] = mark;

	printb (b);
}


int
main (void)
{

	int b[3][3];
	memset (b, 0, sizeof (b));

	printb (b);

	while (1) {
		usermove (b, MO);
		if (gameover_p (b))
			break;

		negamax (b, MX, 1);
		printb (b);
		if (gameover_p (b))
			break;
	}

	if (win_p (b, MX))
		printf ("X wins\n");
	else if (win_p (b, MO))
		printf ("O wins\n");
	else
		printf ("draw\n");

	return 0;
}