#include <stdio.h>
#include <stdlib.h>
#include <time.h>

char grid[3][3];
void showGrid();
void clearGrid();
char checkWinner();

int getOWin();
int preventXWin();

char currentWinner;
char currentPlayer;

int main(){
    int location = 0;

    srand(time(0));

    bool legalMove;
    int choice;
    currentPlayer = 'X';
    int tie=0, xWin=0, oWin=0;
    int mode;

    do{
    printf("Enter '1' for single-player mode, or '2' for two-player mode: ");
    scanf("%i",&mode);
    }while((mode != 1)&&(mode != 2));


    do{
        currentWinner = '.';
        clearGrid();
        showGrid();
        do{
             if((mode == 1)&&(currentPlayer=='O')){

                 printf("Computer plays.\n");

                 location = getOWin();
                 if(location == -1){
                     location = preventXWin();
                     if(location == -1){
                          location = rand()%9;
                     }
                 }

                 do{
                     if((grid[location/3][location%3]!='X')&&(grid[location/3][location%3]!='O')&&(location>=0)&&(location<=8)){
                          legalMove = true;
                     }
                     else{
                          legalMove = false;
                          location = rand()%9;
                     }

                 }while(!legalMove);
             }
             else{
             printf("Player %c, please choose a valid location: ",currentPlayer);
             scanf("%i",&location);
             location--;
             }

             if((grid[location/3][location%3]!='X')&&(grid[location/3][location%3]!='O')&&(location>=0)&&(location<=8)){
                   grid[location/3][location%3] = currentPlayer;
                   legalMove = true;
             }
             else{
                  legalMove = false;
             }

             showGrid();

             if(legalMove){
                 currentWinner = checkWinner();

                 if(currentPlayer == 'X'){
                       currentPlayer = 'O';
                 }
                 else{
                       currentPlayer = 'X';
                 }
             }
             else{
                  printf("Illegal move.\n");
             }

        }while(currentWinner=='.');
        if(currentWinner=='Z'){
             printf("Game is a tie.\n");
             tie++;
        }
        else{
             printf("Winner of this round is player: %c\n",currentWinner);
             if(currentWinner == 'X'){
                 xWin++;
             }
             else{
                 oWin++;
             }
        }
        printf("Press '1' to continue, or any other number to quit: ");
        scanf("%i",&choice);
    }while(choice==1);

    printf("X wins: %i, O wins: %i, tie game: %i\n\n", xWin, oWin, tie);

    printf("Press any key followed by enter to exit: ");
    scanf("%c",&currentWinner);
    return 0;
}

int getOWin(){
    int i;
    int loc = -1;
    char win;
    char prev;

    for(i = 0; i<9; i++){
          prev = grid[i/3][i%3];
            if((grid[i/3][i%3]!='X')&&(grid[i/3][i%3]!='O')){

                  grid[i/3][i%3] = 'O';
                  win = checkWinner();
                  if(win == 'O'){
                         loc = i;
                  }
            }
            grid[i/3][i%3] = prev;
    }
    return loc;
}

int preventXWin(){
    int i;
    int loc = -1;
    char win;
    char prev;

    for(i = 0; i<9; i++){
          prev = grid[i/3][i%3];
            if((grid[i/3][i%3]!='X')&&(grid[i/3][i%3]!='O')){

                  grid[i/3][i%3] = 'X';
                  win = checkWinner();
                  if(win == 'X'){
                         loc = i;
                  }
            }
            grid[i/3][i%3] = prev;
    }
    return loc;
}

char checkWinner(){
     int i, j;
     char cW = '.';
     for(i=0;i<3;i++){
           if((grid[i][0]==grid[i][1])&&(grid[i][0]==grid[i][2])){
                 cW = grid[i][0];
           }
           if((grid[0][i]==grid[1][i])&&(grid[0][i]==grid[2][i])){
                 cW = grid[0][i];
           }
     }

     if((grid[0][0]==grid[1][1])&&(grid[0][0]==grid[2][2])){
           cW = grid[0][0];
     }
     if((grid[0][2]==grid[1][1])&&(grid[0][2]==grid[2][0])){
           cW = grid[0][2];
     }

     bool noEmptySpots = true;
     if(cW == '.'){
           for(i=0;i<3;i++){
             for(j=0;j<3;j++){
                 if((grid[i][j]!='X')&&(grid[i][j]!='O')){
                      noEmptySpots = false;
                 }
             }
           }
           if(noEmptySpots){
             cW = 'Z';
           }
     }

     return cW;
}

void clearGrid(){
     int i, j;
     for(i=0;i<3;i++){
         for(j=0;j<3;j++){
             grid[i][j] = (i*3)+j+49;
         }
     }
}

void showGrid(){
     printf("+---+---+---+\n");
     printf("| %c | %c | %c |\n",grid[0][0],grid[0][1],grid[0][2]);
     printf("+---+---+---+\n");
     printf("| %c | %c | %c |\n",grid[1][0],grid[1][1],grid[1][2]);
     printf("+---+---+---+\n");
     printf("| %c | %c | %c |\n",grid[2][0],grid[2][1],grid[2][2]);
     printf("+---+---+---+\n");
}