#include <iostream>
#include <ctype.h>
#include <stdlib.h>
#include <stdio.h>
#include <string>
#include <sstream>
#include <time.h>

//This function initializes a nine-char grid with underscores
void setGrid ( char grid [] )
{

    for ( int i = 0; i < 9; i++ )
    {
        grid[i] = '_';
    }
}

//This function prints the grid
void showGrid ( char grid [] )
{
    std::cout << "\n";
    for ( int i = 0; i < 9; i++ )
    {
        if ( i == 3 || i == 6 )
        {
            std::cout << "\n";
        }
        std::cout << grid[i] << " ";
    }
    std::cout << "\n";
}

//This function ensures player's input is valid
int checkInput ( char input [] )
{
    int iInput;
    while ( !isdigit(input[0]) )
    {
        std::cout << "Please enter a valid number: ";
        std::cin >> input;
    }
    iInput = std::atoi ( input );
    return iInput;
}

//This function generates a random play for the computer, based on player's moves
int computerCheck ( char grid [] )
{
    std::srand ( time (NULL) );

    for ( int i = 0; i < 9; i+=3 )  //Note i+=3 iterator to check row by row
    {
        if ( grid[i] == 'x' )
        {
            if ( grid[i+1] == 'x' && grid[i+2] == '_' )
                return i + 3;
            else if ( grid[i+1] == '_' && grid[i+2] == 'x' )
                return i + 2;
        }
        else if ( grid[i] == '_' )
        {
            if ( grid[i+1] == 'x' && grid[i+2] == 'x' )
                return i + 1;
        }
    }
    for ( int j = 0; j < 3; j++ )   //checks columns
    {
        if ( grid[j] == 'x' )
        {
            if ( grid[j+3] == 'x' && grid[j+6] == '_' )
                return j + 7;
            else if ( grid[j+3] == '_' && grid[j+6] == 'x' )
                return j + 4;
        }
        else if ( grid[j] == '_' )
        {
            if ( grid[j+3] == 'x' && grid[j+6] == 'x' )
                return j + 1;
        }
    }
    return rand() % 9 + 1;
}

//This function generates the computer's play
char computerPlay ( char grid [] )
{
    std::string result;
    char toReturn;
    int compGuess = computerCheck ( grid );

    std::ostringstream convert;
    convert << compGuess;
    result = convert.str();
    toReturn = result[0];
    return toReturn;
}

//This function plays any square, whether user or computer
void playSquare ( char grid [], char player, char input [] )
{
    int iInput = checkInput ( input );
    while ( iInput < 1 || iInput > 9 )
    {
        std::cout << "That number doesn't work. Try again: ";
        if ( player == 'x' )
            std::cin >> input;
        else
        {
            input[0] = computerPlay ( grid );
            std::cout << input;
        }
        iInput = checkInput ( input );
    }
    while ( grid[iInput-1] != '_' )
    {
        std::cout << "That spot's been taken. Try again: ";
        if ( player == 'x' )
            std::cin >> input;
        else
        {
            input[0] = computerPlay ( grid );
            std::cout << input;
        }
        iInput = checkInput ( input );
    }
    grid[iInput-1] = player;
}

//This function checks the grid for a winner
bool checkGrid ( char grid [], char player )
{
    if ( grid[0] == player )
    {
        if ( grid[1] == player && grid[2] == player )
            return true;
        else if ( grid[3] == player && grid[6] == player )
            return true;
        else if ( grid[4] == player && grid[8] == player )
            return true;
    }
    if ( grid[1] == player )
    {
         if ( grid[4] == player && grid[7] == player )
            return true;
    }
    if ( grid[2] == player )
    {
                if ( grid[4] == player && grid[6] == player )
                            return true;
                else if ( grid[5] == player && grid[8] == player )
                            return true;
    }
    if ( grid[3] == player )
    {
                if ( grid[4] == player && grid[5] == player )
                            return true;
    }
    if ( grid[6] == player )
    {
                if ( grid[7] == player && grid[8] == player )
                            return true;
    }

    return false;
}

//main function
int main() {

    //variable declarations
    char p1x = 'x';
    char p2o = 'o';
    bool isOver = false;
    int counter = 0;
    char userInput [100];
    char gameGrid [9];
    std::string winner = "It's a draw!";


        //initialization
    std::cout << "Time to play some Tic Tac Toe! Enter the number for where you want to place your mark (1 for upper-left, 5 for middle, 9 for lower-right, etc.)\n";
    setGrid ( gameGrid );
    showGrid ( gameGrid );

    //main algorithm
    while ( !isOver || counter < 9 )
    {
        std::cout << "Player 1, enter your number: ";
        std::cin >> userInput;
        playSquare ( gameGrid, p1x, userInput );
        showGrid ( gameGrid );
        isOver = checkGrid ( gameGrid, p1x );
    counter++;
        if ( isOver )
        {
            winner = "Player 1 wins!";
            break;
        }

    if ( counter == 9 ) break;

    std::cout << "Computer's pick: ";
    userInput[0] = computerPlay ( gameGrid );
        std::cout << userInput;
    playSquare ( gameGrid, p2o, userInput );
    showGrid ( gameGrid );
        isOver = checkGrid ( gameGrid, p2o );
        if ( isOver )
        {
            winner = "Player 2 wins!";
            break;
        }
    counter++;
    };
    std::cout << "Game over. " << winner;
    std::cin >> counter;
    return 0;
}