#include <stdio.h>

int check_board(char[][]);
void check_winner(int);
int check_badmove(char[][], int, int);
char switch_curr_player(char);
void draw_board(char[][]);


main() {

  /* declare all main variables */
  char board[3][3];
  int i,j, done, rc, movedone;
  int nummoves;
  int xmove, ymove;
  char curr_player;
  int computer;
  
  /* initialize board to the character '_' */
  for(i=0; i<3; i++) {
    for (j=0; j<3; j++) {
      board[i][j] = '_';
    }
  }  

  /* seed the random number generator */
  srand(time(NULL));

  printf("0 - player versus player\n");
  printf("1 - player versus computer\n");
  printf("Please enter game mode (0 or 1): ");
  scanf("%d", &computer);
  if (computer < 0 || computer > 1) {
    printf("you must choose either mode 0 or 1\n");
    exit(1);
  }

  /* call the draw_board function to draw the playing board */
  draw_board(board);

  /* initialize loop variables */
  nummoves = 0;
  done = 0;
  curr_player = 'X';

  /* outer loop, goes until sombody wins or there is a draw */
  while(!done) {

    /* inner loop: ask cuur player to make a move, if invalid move is made, ask again */
    movedone = 0;
    while(!movedone) {

      xmove = ymove = -1;

      if (computer && curr_player == 'O') {
	while(check_badmove(board, xmove, ymove)) {
	  xmove = rand()%3;
	  ymove = rand()%3;
	}
      } else {
	printf("player %c: enter a move in x,y coordinates (x,y): ", curr_player);
	scanf("%d,%d", &xmove, &ymove);
      }

      /* check if inputted move is valid */
      if (check_badmove(board, xmove, ymove)) {
	printf("player %c: Illegal move, try again!\n", curr_player);
      } else {
	/* fill in the board with curr_player's symbol */
	board[xmove][ymove] = curr_player;
	nummoves++;	
	movedone++;
	printf("Player %c plays at (%d,%d)\n", curr_player, xmove, ymove);
      }

      draw_board(board);
    }
    
     
    /* check to see if the last move found a winner! */
    rc = check_board(board);
    if (rc) {
      check_winner(rc);
      done++;
    }

    if (nummoves == 9) {
      printf("Draw!\n");
      done++;
    }
    /* switch to whomever makes the next move */
    curr_player = switch_curr_player(curr_player);
  }

}

char switch_curr_player(char curr) {
  if (curr == 'X') {
    return('O');
  }
  return('X');
}

int check_badmove(char inboard[3][3], int xmove, int ymove) {
  int rc;
  rc = 0;

  if (inboard[xmove][ymove] != '_') {
    rc = 1;
  } else if (xmove > 2 || xmove < 0) {
    rc = 1;
  } else if (ymove > 2 || ymove < 0) {
    rc = 1;
  }
  return(rc);
}

void check_winner(int winner) {
    switch(winner) {
    case 1:
      printf("X wins!\n");
      break;
    case 2: 
      printf("O wins!\n");
      break;
    default:
      printf("no winner yet\n");
      break;
    }
}  

int check_board(char inboard[3][3]) {
  int i, diagidx;
  int rc;
  int xdiaga, xdiagb, odiaga, odiagb;

  xdiaga = xdiagb = odiaga = odiagb = 1;
  diagidx = 0;
  rc = 0;
  for (i=0; i<3; i++) {
    if (inboard[i][0] == 'X' && inboard[i][1] == 'X' && inboard[i][2] == 'X') {
      rc = 1;
    } else if (inboard[i][0] == 'O' && inboard[i][1] == 'O' && inboard[i][2] == 'O') {
      rc = 2;
    }

    if (inboard[0][i] == 'X' && inboard[1][i] == 'X' && inboard[2][i] == 'X') {
      rc = 1;
      
    } else if (inboard[0][i] == 'O' && inboard[1][i] == 'O' && inboard[2][i] == 'O') {
      rc = 2;
    }


    switch(inboard[i][diagidx]) {
    case 'X':
      odiaga = 0;
      break;
    case 'O':
      xdiaga = 0;
      break;
    default:
      xdiaga = odiaga = 0;
      break;
    }

    switch (inboard[2-i][diagidx]) {
    case 'X':
      odiagb = 0;
      break;
    case 'O':
      xdiagb = 0;
      break;
    default:
      xdiagb = odiagb = 0;
      break;
    }

    diagidx++;
    if (rc) {
      break;
    }

  }

  
  if (xdiaga || xdiagb) {
    rc = 1;
  } else if (odiaga || odiagb) {
    rc = 2;
  }    

  return(rc);
}

void draw_board(char inboard[3][3]) {
  int i, j;
  
  for(i=0; i<3; i++) {
    for (j=0; j<3; j++) {
      printf("| %c ", inboard[i][j]);
    }
    printf("|\n");
  }
}