// I wrote wander.fs but then realized that I had no way to compile it
// to a standalone executable.
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <unistd.h>

enum { width = 80, height = 23 };
char board[height][width];

// Write to standard out, without using stdio
void ws0(char *s)
{
  write(1, s, strlen(s));
}

void print_board()
{
  ws0("\033[H");                // home cursor
  char *p = board[0];
  for (int i = 0; i != height; i++) {
    write(1, p, width);
    ws0("\n");
    p += width;
  }
  ws0("[hjklq]");
}

int dude_x = 40, dude_y = 12;

void init_board()
{
  srand(time(0));
  memset(board[0], ' ', width * height);
  for (int i = 0; i != 512; i++) board[0][rand() % (width * height)] = '#';
  board[dude_y][dude_x] = '@';
}

int clip(int min, int val, int max)
{
  return val < min ? min : val > max ? max : val;
}

void try_move(int dx, int dy)
{
  int x = clip(0, dude_x + dx, width - 1), y = clip(0, dude_y + dy, height - 1);
  if (' ' == board[y][x]) {
    board[dude_y][dude_x] = ' ';
    dude_x = x;
    dude_y = y;
    board[y][x] = '@';
  }
}

int act(int c)
{
  switch(c) {
  case 'h': try_move(-1, 0); break;   case 'l': try_move(1, 0); break;
  case 'j': try_move(0, 1); break;    case 'k': try_move(0, -1); break;
  case 'q': case -1: return 0;
  }
  return 1;
}

int rchar()
{
  char buf;
  if (!read(0, &buf, 1)) return -1; // EOF
  return buf;
}

void wander()
{
  ws0("\033[2J");            // clear screen
  init_board();
  for (;;) {
    print_board();
    if (!act(rchar())) return;
  }
}

int main()
{
  system("stty cbreak -echo");
  wander();
  system("stty -cbreak echo");
  return 0;
}