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

#include "stdio_impl.h"

struct cookie {
  char** bufp;
  size_t* sizep;
  size_t pos;
  char* buf;
  size_t len;
  size_t space;
};

static off_t ms_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 - base)
    goto fail;
  return c->pos = base + off;
}

static size_t ms_write(FILE* f, const unsigned char* buf, size_t len) {
  struct cookie* c = f->cookie;
  size_t len2 = f->wpos - f->wbase;
  char* newbuf;
  if (len2) {
    f->wpos = f->wbase;
    if (ms_write(f, f->wbase, len2) < len2)
      return 0;
  }
  if (len + c->pos >= c->space) {
    len2 = (2 * c->space + 1) | (c->pos + len + 1);
    newbuf = realloc(c->buf, len2);
    if (!newbuf)
      return 0;
    *c->bufp = c->buf = newbuf;
    memset(c->buf + c->space, 0, len2 - c->space);
    c->space = len2;
  }
  memcpy(c->buf + c->pos, buf, len);
  c->pos += len;
  if (c->pos >= c->len)
    c->len = c->pos;
  *c->sizep = c->pos;
  return len;
}

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

FILE* open_memstream(char** bufp, size_t* sizep) {
  FILE* f;
  struct cookie* c;
  char* buf;

  if (!(f = malloc(sizeof *f + sizeof *c + BUFSIZ)))
    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 = BUFSIZ;
  f->lbf = EOF;
  f->write = ms_write;
  f->seek = ms_seek;
  f->close = ms_close;

  return __ofl_add(f);
}