#include <wchar.h>

#include "libc.h"
#include "stdio_impl.h"

static size_t wstring_read(FILE* f, unsigned char* buf, size_t len) {
  const wchar_t* src = f->cookie;
  size_t k;

  if (!src)
    return 0;

  k = wcsrtombs((void*)f->buf, &src, f->buf_size, 0);
  if (k == (size_t)-1) {
    f->rpos = f->rend = 0;
    return 0;
  }

  f->rpos = f->buf;
  f->rend = f->buf + k;
  f->cookie = (void*)src;

  if (!len || !k)
    return 0;

  *buf = *f->rpos++;
  return 1;
}

int vswscanf(const wchar_t* restrict s, const wchar_t* restrict fmt, va_list ap) {
  unsigned char buf[256];
  FILE f = {
      .buf = buf, .buf_size = sizeof buf, .cookie = (void*)s, .read = wstring_read, .lock = -1};
  return vfwscanf(&f, fmt, ap);
}