#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;
}