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

#define N 4

void renderer(int puzzle[N][N]){
    int i, j;

    printf("_____________\n");

    for(i=0;i<N;i++){
        printf("|");
        for(j=0;j<N;j++){
            if(puzzle[i][j]!=16) printf("%2d|", puzzle[i][j]);
            else printf("  |");
        }
        printf("\n");
        printf("_____________\n");
    }
}

void swap(int *a, int *b){
    int temp = *a;
    *a = *b;
    *b = temp;
}

void randomize(int puzzle[N][N], int *posx, int *posy){
    int i, j, x, y;

    srand((unsigned) time(NULL));
    for(i=0;i<N;i++){
        for(j=0;j<N;j++){
            x = rand() % N;
            y = rand() % N;
            swap(&puzzle[y][x], &puzzle[i][j]);
            if (puzzle[y][x] == 16){
                *posx = x;
                *posy = y;
            }
            else if (puzzle[i][j] == 16){
                *posx = j;
                *posy = i;
            }

        }
    }
}

int wincheck(int puzzle[N][N]){
    int i, j;

    for(i=0;i<N;i++){
        for(j=0;j<N;j++){
            if(puzzle[i][j] != i*4+j+1) return 0;
        }
    }

    return 1;
}

main(){
    int puzzle[N][N], x, y, i, j;
    char ch;

    for(i=0;i<N;i++){
        for (j=0;j<N;j++){
            puzzle[i][j] = i*4+j+1;
        }
    }

    randomize(puzzle, &x, &y);

    while(ch != 27){
        renderer(puzzle);
        if(wincheck(puzzle)){printf("You win!\n"); break;}
        printf("Your move: ");
        ch = getchar();
        ch = toupper(ch);
        switch (ch){
            case 'W':{
                if(y+1 < N){swap(&puzzle[y][x], &puzzle[y+1][x]); y++;}
                else printf("Illegal move.\n");
                break; }
            case 'A':{
                if(x+1 < N){swap(&puzzle[y][x], &puzzle[y][x+1]); x++;}
                else printf("Illegal move.\n");
                break;}
            case 'S':{
                if(y-1 >=0){swap(&puzzle[y][x], &puzzle[y-1][x]); --y;}
                else printf("Illegal move.\n");
                break;}
            case 'D':{
                if(x-1 >=0){swap(&puzzle[y][x], &puzzle[y][x-1]); --x;}
                else printf("Illegal move.\n");
                break;}
            case 27:{printf("Exiting...\n"); break;}
            default: printf("Invalid input.\n");
        }
        getchar();
    }

    return 0;
}