#include <unistd.h>
#include <sys/stat.h>

extern int _end;
void* _sbrk(int incr);
int _close(int file);
int _fstat(int file, struct stat *st);
int _isatty(int fd);
int _lseek(int file, int ptr, int dir);

void _kill(int pid, int sig);
int _getpid(void);
void write_hex(int fd, unsigned long int hex);

void *_sbrk(int incr) {
  static unsigned char *heap = NULL;
  unsigned char *prev_heap;
  if (heap == NULL) {
    heap = (unsigned char *)&_end;
  }
  prev_heap = heap;
  heap += incr;
  return prev_heap;
}

int _close(int file) {
  (void)file;
  return -1;
}

int _fstat(int file, struct stat *st) {
  (void)file;
  st->st_mode = S_IFCHR;
  return 0;
}

int _isatty(int fd) {
  if (fd == STDOUT_FILENO || fd == STDERR_FILENO)
    return 1;
  return 0;
}

int _lseek(int file, int ptr, int dir) {
  (void)file;
  (void)ptr;
  (void)dir;
  return 0;
}

void _exit(int status) {
  const char message[] = "\nProgam has exited with code:";
  write(STDERR_FILENO, message, sizeof(message) - 1);
  write_hex(STDERR_FILENO, status);
  write(STDERR_FILENO, "\n", 1);
  for (;;);
}

void _kill(int pid, int sig) {
  (void)pid;
  (void)sig;
  return;
}

int _getpid(void) {
  return -1;
}

void write_hex(int fd, unsigned long int hex){
  uint8_t ii;
  uint8_t jj;
  char towrite;
  write(fd , "0x", 2);
  for (ii = sizeof(unsigned long int) * 2 ; ii > 0; ii--) {
    jj = ii - 1;
    uint8_t digit = ((hex & (0xF << (jj*4))) >> (jj*4));
    towrite = digit < 0xA ? ('0' + digit) : ('A' +  (digit - 0xA));
    write(fd, &towrite, 1);
  }
}