#include <errno.h>
#include <limits.h>
#include <string.h>
#include <wchar.h>

#include "stdio_impl.h"

struct cookie {
  wchar_t** bufp;
  size_t* sizep;
  size_t pos;
  wchar_t* buf;
  size_t len;
  size_t space;
  mbstate_t mbs;
};

static off_t wms_seek(FILE* f, off_t off, int whence) {
  ssize_t base;
  struct cookie* c = f->cookie;
  if (whence > 2U) {
  fail:
    errno = EINVAL;
    return -1;
  }
  base = (size_t[3]){0, c->pos, c->len}[whence];
  if (off < -base || off > SSIZE_MAX / 4 - base)
    goto fail;
  memset(&c->mbs, 0, sizeof c->mbs);
  return c->pos = base + off;
}

static size_t wms_write(FILE* f, const unsigned char* buf, size_t len) {
  struct cookie* c = f->cookie;
  size_t len2;
  wchar_t* newbuf;
  if (len + c->pos >= c->space) {
    len2 = (2 * c->space + 1) | (c->pos + len + 1);
    if (len2 > SSIZE_MAX / 4)
      return 0;
    newbuf = realloc(c->buf, len2 * 4);
    if (!newbuf)
      return 0;
    *c->bufp = c->buf = newbuf;
    memset(c->buf + c->space, 0, 4 * (len2 - c->space));
    c->space = len2;
  }

  len2 = mbsnrtowcs(c->buf + c->pos, (void*)&buf, len, c->space - c->pos, &c->mbs);
  if (len2 == -1)
    return 0;
  c->pos += len2;
  if (c->pos >= c->len)
    c->len = c->pos;
  *c->sizep = c->pos;
  return len;
}

static int wms_close(FILE* f) { return 0; }

FILE* open_wmemstream(wchar_t** bufp, size_t* sizep) {
  FILE* f;
  struct cookie* c;
  wchar_t* buf;

  if (!(f = malloc(sizeof *f + sizeof *c)))
    return 0;
  if (!(buf = malloc(sizeof *buf))) {
    free(f);
    return 0;
  }
  memset(f, 0, sizeof *f + sizeof *c);
  f->cookie = c = (void*)(f + 1);

  c->bufp = bufp;
  c->sizep = sizep;
  c->pos = c->len = c->space = *sizep = 0;
  c->buf = *bufp = buf;
  *buf = 0;

  f->flags = F_NORD;
  f->fd = -1;
  f->buf = (void*)(c + 1);
  f->buf_size = 0;
  f->lbf = EOF;
  f->write = wms_write;
  f->seek = wms_seek;
  f->close = wms_close;

  return __ofl_add(f);
}