/**
 * fifteen.c
 *
 * Computer Science 50
 * Problem Set 3
 *
 * Implements Game of Fifteen (generalized to d x d).
 *
 * Usage: fifteen d
 *
 * whereby the board's dimensions are to be d x d,
 * where d must be in [DIM_MIN,DIM_MAX]
 *
 * Note that usleep is obsolete, but it offers more granularity than
 * sleep and is simpler to use than nanosleep; `man usleep` for more.
 */

#define _XOPEN_SOURCE 500

#include <cs50.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

// constants
#define DIM_MIN 3
#define DIM_MAX 9

// board
int board[DIM_MAX][DIM_MAX];

// dimensions
int d;

// prototypes
void clear(void);
void greet(void);
void init(void);
void draw(void);
bool move(int tile);
bool won(void);

int main(int argc, string argv[])
{
    // ensure proper usage
    if (argc != 2)
    {
        printf("Usage: fifteen d\n");
        return 1;
    }

    // ensure valid dimensions
    d = atoi(argv[1]);
    if (d < DIM_MIN || d > DIM_MAX)
    {
        printf("Board must be between %i x %i and %i x %i, inclusive.\n",
            DIM_MIN, DIM_MIN, DIM_MAX, DIM_MAX);
        return 2;
    }

    // open log
    FILE* file = fopen("log.txt", "w");
    if (file == NULL)
    {
        return 3;
    }

    // greet user with instructions
    greet();

    // initialize the board
    init();

    // accept moves until game is won
    while (true)
    {
        // clear the screen
        clear();

        // draw the current state of the board
        draw();

        // log the current state of the board (for testing)
        for (int i = 0; i < d; i++)
        {
            for (int j = 0; j < d; j++)
            {
                fprintf(file, "%i", board[i][j]);
                if (j < d - 1)
                {
                    fprintf(file, "|");
                }
            }
            fprintf(file, "\n");
        }
        fflush(file);

        // check for win
        if (won())
        {
            printf("ftw!\n");
            break;
        }

        // prompt for move
        printf("Tile to move: ");
        int tile = GetInt();

        // quit if user inputs 0 (for testing)
        if (tile == 0)
        {
            break;
        }

        // log move (for testing)
        fprintf(file, "%i\n", tile);
        fflush(file);

        // move if possible, else report illegality
        if (!move(tile))
        {
            printf("\nIllegal move.\n");
            usleep(500000);
        }

        // sleep thread for animation's sake
        usleep(500000);
    }

    // close log
    fclose(file);

    // success
    return 0;
}

/**
 * Clears screen using ANSI escape sequences.
 */
void clear(void)
{
    printf("\033[2J");
    printf("\033[%d;%dH", 0, 0);
}

/**
 * Greets player.
 */
void greet(void)
{
    clear();
    printf("WELCOME TO GAME OF FIFTEEN\n");
    usleep(2000000);
}

/**
 * Initializes the game's board with tiles numbered 1 through d*d - 1
 * (i.e., fills 2D array with values but does not actually print them).
 */
void init(void)
{   int counter = d*d-1;
    // TODO
    for(int i=0;i<d;i++)
    {
        for(int j=0;j<d;j++)
        {  if(counter>=0)
            {
              board[i][j] = counter;
              if(d%2 ==0)
              {
                  if(counter==2)
                  {
                    board[i][j+1] = 2;
                    board[i][j] = 1;
                  }
              }
              counter--;
            }

        }
    }
}

/**
 * Prints the board in its current state.
 */
void draw(void)
{
    // TODo
    for(int i=0;i<d;i++)
    {
        for(int j=0;j<d;j++)
        {  if(board[i][j]>0)
            {
              printf("%d",board[i][j]);
            }
            else if (board[i][j]==0)
            {
                printf("_");
            }

        }
    }
}

/**
 * If tile borders empty space, moves tile and returns true, else
 * returns false.
 */
bool move(int tile)
{
    // TODO
       int i,j,a,b,swap;
    for( i=0;i<d;i++)
    {
        for( j=0;j<d;j++)
      {  if(board[i][j]==0)
        {
            a=i;
            b=j;
        }
      }
    }
    for( i=0;i<d;i++)
    {
        for( j=0;j<d;j++)
      {
        if(board[i][j]==tile)
        {
            if((i==a||i==(a-1)||i==(a+1))&&(j==b||j==(b-1)||j==(b+1)))
            {
                if(i>=0&&j>=0&&i<d&&j<d)
                {
                    swap=board[a][b];
                    board[a][b]=board[i][j];
                    board[i][j]=swap;
                    return true;
                }
                else
                    return false;
            }
        }
      }
    }
    return false;
}

/**
 * Returns true if game is won (i.e., board is in winning configuration),
 * else false.
 */
bool won(void)
{
    // TODO
   int i,j,counter=1,a[d][d],flag=0;
   for(i=0;i<d;i++)
   {
       for(j=0;j<d;j++)
       {
           a[i][j]=counter;
           counter++;
       }
   }
   a[d-1][d-1]=0;
   for(i=0;i<d;i++)
   {
       for(j=0;j<d;j++)
       {
           if(board[i][j]==a[i][j])
           {
               flag=0;
           }
           else if(board[i][j]!=a[i][j])
           {
               flag=1;
           }
       }
   }
   if(flag==0)
   return true;
   if(flag==1)
   return false;
}
output:
~/workspace/pset3/fifteen $ make fifteen
clang -ggdb3 -O0 -std=c11 -Wall -Werror -o fifteen fifteen.c -lcs50 -lm
fifteen.c:283:1: error: control may reach end of non-void function [-Werror,-Wreturn-type]
}
^
1 error generated.
make: *** [fifteen] Error 1