#include "stdio_impl.h"
#include <errno.h>
#include <string.h>
#include <inttypes.h>

struct cookie {
  size_t pos, len, size;
  unsigned char* buf;
  int mode;
};

static off_t mseek(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_t)c->size - base)
    goto fail;
  return c->pos = base + off;
}

static size_t mread(FILE* f, unsigned char* buf, size_t len) {
  struct cookie* c = f->cookie;
  size_t rem = c->len - c->pos;
  if (c->pos > c->len)
    rem = 0;
  if (len > rem) {
    len = rem;
    f->flags |= F_EOF;
  }
  memcpy(buf, c->buf + c->pos, len);
  c->pos += len;
  rem -= len;
  if (rem > f->buf_size)
    rem = f->buf_size;
  f->rpos = f->buf;
  f->rend = f->buf + rem;
  memcpy(f->rpos, c->buf + c->pos, rem);
  c->pos += rem;
  return len;
}

static size_t mwrite(FILE* f, const unsigned char* buf, size_t len) {
  struct cookie* c = f->cookie;
  size_t rem;
  size_t len2 = f->wpos - f->wbase;
  if (len2) {
    f->wpos = f->wbase;
    if (mwrite(f, f->wpos, len2) < len2)
      return 0;
  }
  if (c->mode == 'a')
    c->pos = c->len;
  rem = c->size - c->pos;
  if (len > rem)
    len = rem;
  memcpy(c->buf + c->pos, buf, len);
  c->pos += len;
  if (c->pos > c->len) {
    c->len = c->pos;
    if (c->len < c->size)
      c->buf[c->len] = 0;
    else if ((f->flags & F_NORD) && c->size)
      c->buf[c->size - 1] = 0;
  }
  return len;
}

static int mclose(FILE* m) {
  return 0;
}

FILE* fmemopen(void* restrict buf, size_t size, const char* restrict mode) {
  FILE* f;
  struct cookie* c;
  int plus = !!strchr(mode, '+');

  if (!size || !strchr("rwa", *mode)) {
    errno = EINVAL;
    return 0;
  }

  if (!buf && size > SIZE_MAX - sizeof(FILE) - BUFSIZ - UNGET) {
    errno = ENOMEM;
    return 0;
  }

  f = calloc(sizeof *f + sizeof *c + UNGET + BUFSIZ + (buf ? 0 : size), 1);
  if (!f)
    return 0;
  f->cookie = c = (void*)(f + 1);
  f->fd = -1;
  f->lbf = EOF;
  f->buf = (unsigned char*)(c + 1) + UNGET;
  f->buf_size = BUFSIZ;
  if (!buf)
    buf = f->buf + BUFSIZ;

  c->buf = buf;
  c->size = size;
  c->mode = *mode;

  if (!plus)
    f->flags = (*mode == 'r') ? F_NOWR : F_NORD;
  if (*mode == 'r')
    c->len = size;
  else if (*mode == 'a')
    c->len = c->pos = strnlen(buf, size);

  f->read = mread;
  f->write = mwrite;
  f->seek = mseek;
  f->close = mclose;

  if (!libc.threaded)
    f->lock = -1;

  return __ofl_add(f);
}