/* -------------------------------------------------------------------------
 * This file is part of LMDB - Erlang Lightning MDB API
 *
 * Copyright (c) 2012 by Aleph Archives. All rights reserved.
 * Copyright (c) 2013 by Basho Technologies, Inc. All rights reserved.
 *
 * -------------------------------------------------------------------------
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted only as authorized by the OpenLDAP
 * Public License.
 *
 * A copy of this license is available in the file LICENSE in the
 * top-level directory of the distribution or, alternatively, at
 * <http://www.OpenLDAP.org/license.html>.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 * -------------------------------------------------------------------------*/

#include <stdio.h>
#include <string.h>
#include <inttypes.h>
#include <errno.h>
#include <sys/param.h>
#include <erl_nif.h>
#include <erl_driver.h>

#include "common.h"
#include "async_nif.h"
#include "lmdb.h"

static ErlNifResourceType *lmdb_RESOURCE;
struct lmdb {
    MDB_env *env;
    MDB_txn *txn;
    MDB_cursor *cursor;
    MDB_dbi dbi;
};

struct lmdb_priv_data {
    void *async_nif_priv; // Note: must be first element in struct
};

/* Global init for async_nif. */
ASYNC_NIF_INIT(lmdb);

/* Atoms (initialized in on_load) */
static ERL_NIF_TERM ATOM_ERROR;
static ERL_NIF_TERM ATOM_OK;
static ERL_NIF_TERM ATOM_NOT_FOUND;
static ERL_NIF_TERM ATOM_EXISTS;
static ERL_NIF_TERM ATOM_KEYEXIST;
static ERL_NIF_TERM ATOM_NOTFOUND;
static ERL_NIF_TERM ATOM_PAGE_NOTFOUND;
static ERL_NIF_TERM ATOM_CORRUPTED;
static ERL_NIF_TERM ATOM_PANIC;
static ERL_NIF_TERM ATOM_VERSION_MISMATCH;
static ERL_NIF_TERM ATOM_KEYEXIST;
static ERL_NIF_TERM ATOM_MAP_FULL;
static ERL_NIF_TERM ATOM_DBS_FULL;
static ERL_NIF_TERM ATOM_READERS_FULL;
static ERL_NIF_TERM ATOM_TLS_FULL;
static ERL_NIF_TERM ATOM_TXN_FULL;
static ERL_NIF_TERM ATOM_CURSOR_FULL;
static ERL_NIF_TERM ATOM_PAGE_FULL;
static ERL_NIF_TERM ATOM_MAP_RESIZED;
static ERL_NIF_TERM ATOM_INCOMPATIBLE;
static ERL_NIF_TERM ATOM_BAD_RSLOT;

static ERL_NIF_TERM ATOM_TXN_STARTED;
static ERL_NIF_TERM ATOM_TXN_NOT_STARTED;

#define CHECK(expr, label)						\
    if (MDB_SUCCESS != (ret = (expr))) {				\
	DPRINTF("CHECK(\"%s\") failed \"%s\" at %s:%d in %s()\n",	\
	        #expr, mdb_strerror(ret), __FILE__, __LINE__, __func__);\
	err = __strerror_term(env, ret);				\
	goto label;							\
    }

#define FAIL_ERR(e, label)				\
    do {						\
	err = __strerror_term(env, (e));		\
	goto label;					\
    } while(0)

/**
 * Convenience function to generate {error, {errno, Reason}}
 *
 * env    NIF environment
 * err    number of last error
 */
static ERL_NIF_TERM
__strerror_term(ErlNifEnv* env, int err)
{
    ERL_NIF_TERM term;

    if (err < MDB_LAST_ERRCODE && err > MDB_KEYEXIST) {
	switch (err) {
	case MDB_KEYEXIST: /** key/data pair already exists */
	    term = ATOM_KEYEXIST;
	    break;
	case MDB_NOTFOUND: /** key/data pair not found (EOF) */
	    term = ATOM_NOTFOUND;
	    break;
	case MDB_PAGE_NOTFOUND: /** Requested page not found - this usually indicates corruption */
	    term = ATOM_PAGE_NOTFOUND;
	    break;
	case MDB_CORRUPTED: /** Located page was wrong type */
	    term = ATOM_CORRUPTED;
	    break;
	case MDB_PANIC	: /** Update of meta page failed, probably I/O error */
	    term = ATOM_PANIC;
	    break;
	case MDB_VERSION_MISMATCH: /** Environment version mismatch */
	    term = ATOM_VERSION_MISMATCH;
	    break;
	case MDB_INVALID: /** File is not a valid MDB file */
	    term = ATOM_KEYEXIST;
	    break;
	case MDB_MAP_FULL: /** Environment mapsize reached */
	    term = ATOM_MAP_FULL;
	    break;
	case MDB_DBS_FULL: /** Environment maxdbs reached */
	    term = ATOM_DBS_FULL;
	    break;
	case MDB_READERS_FULL: /** Environment maxreaders reached */
	    term = ATOM_READERS_FULL;
	    break;
	case MDB_TLS_FULL: /** Too many TLS keys in use - Windows only */
	    term = ATOM_TLS_FULL;
	    break;
	case MDB_TXN_FULL: /** Txn has too many dirty pages */
	    term = ATOM_TXN_FULL;
	    break;
	case MDB_CURSOR_FULL: /** Cursor stack too deep - internal error */
	    term = ATOM_CURSOR_FULL;
	    break;
	case MDB_PAGE_FULL: /** Page has not enough space - internal error */
	    term = ATOM_PAGE_FULL;
	    break;
	case MDB_MAP_RESIZED: /** Database contents grew beyond environment mapsize */
	    term = ATOM_MAP_RESIZED;
	    break;
	case MDB_INCOMPATIBLE: /** Database flags changed or would change */
	    term = ATOM_INCOMPATIBLE;
	    break;
	case MDB_BAD_RSLOT: /** Invalid reuse of reader locktable slot */
	    term = ATOM_BAD_RSLOT;
	    break;
	}
    } else {
	term = enif_make_atom(env, erl_errno_id(err));
    }

    /* We return the errno value as well as the message here because the error
       message provided by strerror() for differ across platforms and/or may be
       localized to any given language (i18n).  Use the errno atom rather than
       the message when matching in Erlang.  You've been warned. */
    return enif_make_tuple(env, 2, ATOM_ERROR,
		enif_make_tuple(env, 2, term,
		     enif_make_string(env, mdb_strerror(err), ERL_NIF_LATIN1)));
}

/**
 * Opens a MDB database.
 *
 * argv[0]    path to directory for the database files
 * argv[1]    size of database
 * argv[2]    flags
 */
ASYNC_NIF_DECL(
  lmdb_open,
  { // struct

      char dirname[MAXPATHLEN];
      ErlNifUInt64 mapsize;
      ErlNifUInt64 envflags;
  },
  { // pre
      if (!(argc == 3 &&
	    enif_is_list(env, argv[0]) &&
	    enif_is_number(env, argv[1]) &&
	    enif_is_number(env, argv[2]))) {
	  ASYNC_NIF_RETURN_BADARG();
      }
      if (enif_get_string(env, argv[0], args->dirname,
			  MAXPATHLEN, ERL_NIF_LATIN1) <= 0)
	  ASYNC_NIF_RETURN_BADARG();
      enif_get_uint64(env, argv[1], &(args->mapsize));
      enif_get_uint64(env, argv[2], &(args->envflags));
  },
  { // work

      ERL_NIF_TERM err;
      MDB_txn *txn;
      struct lmdb *handle;
      int ret;

      if ((handle = enif_alloc_resource(lmdb_RESOURCE, sizeof(struct lmdb))) == NULL)
	  FAIL_ERR(ENOMEM, err3);

      CHECK(mdb_env_create(&(handle->env)), err2);

      if (mdb_env_set_mapsize(handle->env, args->mapsize)) {
	  ASYNC_NIF_REPLY(enif_make_badarg(env));
	  return;
      }

      CHECK(mdb_env_open(handle->env, args->dirname, args->envflags, 0664), err2);
      CHECK(mdb_txn_begin(handle->env, NULL, 0, &txn), err2);
      CHECK(mdb_open(txn, NULL, 0, &(handle->dbi)), err1);
      CHECK(mdb_txn_commit(txn), err1);

      handle->txn = NULL;
      handle->cursor = NULL;

      ERL_NIF_TERM term = enif_make_resource(env, handle);
      enif_release_resource(handle);
      ASYNC_NIF_REPLY(enif_make_tuple(env, 2, ATOM_OK, term));
      return;

  err1:
      mdb_txn_abort(txn);
  err2:
      mdb_env_close(handle->env);
  err3:
      ASYNC_NIF_REPLY(err);
      return;
  },
  { // post

  });


/**
 * Closes a MDB database.
 *
 * argv[0]    reference to the MDB handle resource
 */
ASYNC_NIF_DECL(
  lmdb_close,
  { // struct

      struct lmdb *handle;
  },
  { // pre

      if (!(argc == 1 &&
	    enif_get_resource(env, argv[0], lmdb_RESOURCE, (void**)&args->handle))) {
	  ASYNC_NIF_RETURN_BADARG();
      }
      if (!args->handle->env)
	  ASYNC_NIF_RETURN_BADARG();
      enif_keep_resource((void*)args->handle);
  },
  { // work

      mdb_env_close(args->handle->env);
      args->handle->env = NULL;
      ASYNC_NIF_REPLY(ATOM_OK);
      return;
  },
  { // post

    enif_release_resource((void*)args->handle);
  });


/**
 * Store a value indexed by key.
 *
 * argv[0]    reference to the MDB handle resource
 * argv[1]    key as an Erlang binary
 * argv[2]    value as an Erlang binary
 */
ASYNC_NIF_DECL(
  lmdb_put,
  { // struct

      struct lmdb *handle;
      ERL_NIF_TERM key;
      ERL_NIF_TERM val;
  },
  { // pre

      if (!(argc == 3 &&
	    enif_get_resource(env, argv[0], lmdb_RESOURCE, (void**)&args->handle) &&
	    enif_is_binary(env, argv[1]) &&
	    enif_is_binary(env, argv[2]) )) {
	  ASYNC_NIF_RETURN_BADARG();
      }
      if (!args->handle->env)
	  ASYNC_NIF_RETURN_BADARG();
      enif_keep_resource((void*)args->handle);
      args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[1]);
      args->val = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
  },
  { // work

      ERL_NIF_TERM err;
      ErlNifBinary key;
      ErlNifBinary val;
      MDB_val mkey;
      MDB_val mdata;
      MDB_txn * txn;
      int ret;

      if (!enif_inspect_iolist_as_binary(env, args->key, &key)) {
	  ASYNC_NIF_REPLY(enif_make_badarg(env));
	  return;
      }
      if (!enif_inspect_iolist_as_binary(env, args->val, &val)) {
	  ASYNC_NIF_REPLY(enif_make_badarg(env));
	  return;
      }

      mkey.mv_size  = key.size;
      mkey.mv_data  = key.data;
      mdata.mv_size = val.size;
      mdata.mv_data = val.data;
      if(args->handle->txn == NULL) {
          CHECK(mdb_txn_begin(args->handle->env, NULL, 0, & txn), err2);
      } else {
          txn = args->handle->txn;
      }

      ret = mdb_put(txn, args->handle->dbi, &mkey, &mdata, MDB_NOOVERWRITE);
      if (MDB_KEYEXIST == ret) {
	  ASYNC_NIF_REPLY(enif_make_tuple(env, 2, ATOM_ERROR, ATOM_EXISTS));
	  return;
      }
      if (ret != 0)
	  FAIL_ERR(ret, err1);

      if(args->handle->txn == NULL)
          CHECK(mdb_txn_commit(txn), err1);
      ASYNC_NIF_REPLY(ATOM_OK);
      return;

  err1:
      mdb_txn_abort(txn);
  err2:
      ASYNC_NIF_REPLY(err);
      return;
  },
  { // post

    enif_release_resource((void*)args->handle);
  });

/**
 * Update and existin value indexed by key.
 *
 * argv[0]    reference to the MDB handle resource
 * argv[1]    key as an Erlang binary
 * argv[2]    value as an Erlang binary
 */
ASYNC_NIF_DECL(
  lmdb_update,
  { // struct

      struct lmdb *handle;
      ERL_NIF_TERM key;
      ERL_NIF_TERM val;
  },
  { // pre

      if (!(argc == 3 &&
	    enif_get_resource(env, argv[0], lmdb_RESOURCE, (void**)&args->handle) &&
	    enif_is_binary(env, argv[1]) &&
	    enif_is_binary(env, argv[2]) )) {
	  ASYNC_NIF_RETURN_BADARG();
      }
      if (!args->handle->env)
	  ASYNC_NIF_RETURN_BADARG();
      enif_keep_resource((void*)args->handle);
      args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[1]);
      args->val = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
  },
  { // work

      ERL_NIF_TERM err;
      ErlNifBinary key;
      ErlNifBinary val;
      MDB_val mkey;
      MDB_val mdata;
      MDB_txn * txn;
      int ret;

      if (!enif_inspect_iolist_as_binary(env, args->key, &key)) {
	  ASYNC_NIF_REPLY(enif_make_badarg(env));
	  return;
      }
      if (!enif_inspect_iolist_as_binary(env, args->val, &val)) {
	  ASYNC_NIF_REPLY(enif_make_badarg(env));
	  return;
      }

      mkey.mv_size  = key.size;
      mkey.mv_data  = key.data;
      mdata.mv_size = val.size;
      mdata.mv_data = val.data;

      if(args->handle->txn == NULL) {
          CHECK(mdb_txn_begin(args->handle->env, NULL, 0, & txn), err2);
      } else {
          txn = args->handle->txn;
      }

      CHECK(mdb_put(txn, args->handle->dbi, &mkey, &mdata, 0), err1);

      if(args->handle->txn == NULL)
          CHECK(mdb_txn_commit(txn), err1);
      ASYNC_NIF_REPLY(ATOM_OK);
      return;

  err1:
      mdb_txn_abort(txn);
  err2:
      ASYNC_NIF_REPLY(err);
      return;
  },
  { // post

    enif_release_resource((void*)args->handle);
  });


/**
 * Retrieve the value associated with the key.
 *
 * argv[0]    reference to the MDB handle resource
 * argv[1]    key as an Erlang binary
 */
ASYNC_NIF_DECL(
  lmdb_get,
  { // struct

      struct lmdb *handle;
      ERL_NIF_TERM key;
  },
  { // pre

      if (!(argc == 2 &&
	    enif_get_resource(env, argv[0], lmdb_RESOURCE, (void**)&args->handle) &&
	    enif_is_binary(env, argv[1]) )) {
	  ASYNC_NIF_RETURN_BADARG();
      }
      if (!args->handle->env)
	  ASYNC_NIF_RETURN_BADARG();
      enif_keep_resource((void*)args->handle);
      args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[1]);
  },
  { // work

      ERL_NIF_TERM err;
      ErlNifBinary key;
      ERL_NIF_TERM val;
      unsigned char *bin;
      MDB_val mkey;
      MDB_val mdata;
      MDB_txn * txn;
      int ret;

      if (!enif_inspect_iolist_as_binary(env, args->key, &key)) {
	  ASYNC_NIF_REPLY(enif_make_badarg(env));
	  return;
      }

      mkey.mv_size  = key.size;
      mkey.mv_data  = key.data;

      if(args->handle->txn == NULL) {
          CHECK(mdb_txn_begin(args->handle->env, NULL, 0, & txn), err);
      } else {
          txn = args->handle->txn;
      }

      ret = mdb_get(txn, args->handle->dbi, &mkey, &mdata);
      if(args->handle->txn == NULL)
          mdb_txn_abort(txn);
      if (MDB_NOTFOUND == ret) {
	  ASYNC_NIF_REPLY(ATOM_NOT_FOUND);
	  return;
      }

      if (ret != 0)
	  FAIL_ERR(ret, err);

      bin = enif_make_new_binary(env, mdata.mv_size, &val);
      if (!bin)
	  FAIL_ERR(ENOMEM, err);
      memcpy(bin, mdata.mv_data, mdata.mv_size);

      ASYNC_NIF_REPLY(enif_make_tuple(env, 2, ATOM_OK, val));
      return;

  err:
      ASYNC_NIF_REPLY(err);
      return;
  },
  { // post

    enif_release_resource((void*)args->handle);
  });


/**
 * Delete the value associated with the key.
 *
 * argv[0]    reference to the MDB handle resource
 * argv[1]    key as an Erlang binary
 */
ASYNC_NIF_DECL(
  lmdb_del,
  { // struct

      struct lmdb *handle;
      ERL_NIF_TERM key;
  },
  { // pre

      if (!(argc == 2 &&
	    enif_get_resource(env, argv[0], lmdb_RESOURCE, (void**)&args->handle) &&
	    enif_is_binary(env, argv[1]) )) {
	  ASYNC_NIF_RETURN_BADARG();
      }
      if (!args->handle->env)
	  ASYNC_NIF_RETURN_BADARG();
      enif_keep_resource((void*)args->handle);
      args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[1]);
  },
  { // work

      ERL_NIF_TERM err;
      ErlNifBinary key;
      MDB_val mkey;
      MDB_txn * txn;
      int ret;

      if (!enif_inspect_iolist_as_binary(env, args->key, &key)) {
	  ASYNC_NIF_REPLY(enif_make_badarg(env));
	  return;
      }

      mkey.mv_size  = key.size;
      mkey.mv_data  = key.data;

      if(args->handle->txn == NULL) {
          CHECK(mdb_txn_begin(args->handle->env, NULL, 0, & txn), err);
      } else {
          txn = args->handle->txn;
      }

      ret = mdb_del(txn, args->handle->dbi, &mkey, NULL);

      if(MDB_NOTFOUND == ret) {
          if(args->handle->txn == NULL)
              mdb_txn_abort(txn);
	  ASYNC_NIF_REPLY(ATOM_NOT_FOUND);
	  return;
      }
      if(args->handle->txn == NULL)
          CHECK(mdb_txn_commit(txn), err);
      ASYNC_NIF_REPLY(ATOM_OK);
      return;

  err:
      ASYNC_NIF_REPLY(err);
      return;
  },
  { // post

    enif_release_resource((void*)args->handle);
  });


/**
 * Drop a MDB database.
 *
 * argv[0]    reference to the MDB handle resource
 */
ASYNC_NIF_DECL(
  lmdb_drop,
  { // struct

      struct lmdb *handle;
  },
  { // pre

      if (!(argc == 1 &&
	    enif_get_resource(env, argv[0], lmdb_RESOURCE, (void**)&args->handle))) {
	  ASYNC_NIF_RETURN_BADARG();
      }
      if (!args->handle->env)
	  ASYNC_NIF_RETURN_BADARG();
      enif_keep_resource((void*)args->handle);
  },
  { // work

      ERL_NIF_TERM err;
      MDB_txn * txn;
      int ret;

      CHECK(mdb_txn_begin(args->handle->env, NULL, 0, & txn), err2);
      CHECK(mdb_drop(txn, args->handle->dbi, 0), err1);
      CHECK(mdb_txn_commit(txn), err1);
      ASYNC_NIF_REPLY(ATOM_OK);
      return;

  err1:
      mdb_txn_abort(txn);

  err2:
      ASYNC_NIF_REPLY(err);
      return;
  },
  { // post

    enif_release_resource((void*)args->handle);
  });

ASYNC_NIF_DECL(
  lmdb_txn_begin,
  { // struct

      struct lmdb *handle;
  },
  { // pre

      if (!(argc == 1 &&
        enif_get_resource(env, argv[0], lmdb_RESOURCE, (void**)&args->handle))) {
      ASYNC_NIF_RETURN_BADARG();
      }
      if (!args->handle->env)
      ASYNC_NIF_RETURN_BADARG();
      enif_keep_resource((void*)args->handle);
  },
  { // work

      ERL_NIF_TERM err;
      int ret;
      if(args->handle->txn == NULL) {
          CHECK(mdb_txn_begin(args->handle->env, NULL, 0, &(args->handle->txn)), err2);
          ASYNC_NIF_REPLY(ATOM_OK);
      } else
          ASYNC_NIF_REPLY(enif_make_tuple(env, 2, ATOM_ERROR, ATOM_TXN_STARTED));
      return;

  err2:
      ASYNC_NIF_REPLY(err);
      return;
  },
  { // post

    enif_release_resource((void*)args->handle);
  });

ASYNC_NIF_DECL(
  lmdb_txn_commit,
  { // struct

      struct lmdb *handle;
  },
  { // pre

      if (!(argc == 1 &&
        enif_get_resource(env, argv[0], lmdb_RESOURCE, (void**)&args->handle))) {
      ASYNC_NIF_RETURN_BADARG();
      }
      if (!args->handle->env)
      ASYNC_NIF_RETURN_BADARG();
      enif_keep_resource((void*)args->handle);
  },
  { // work

      ERL_NIF_TERM err;
      int ret;
      if(args->handle->txn != NULL) {
          CHECK(mdb_txn_commit(args->handle->txn), err2);
          args->handle->txn = NULL;
          ASYNC_NIF_REPLY(ATOM_OK);
      } else
          ASYNC_NIF_REPLY(enif_make_tuple(env, 2, ATOM_ERROR, ATOM_TXN_NOT_STARTED));
      return;

  err2:
      ASYNC_NIF_REPLY(err);
      return;
  },
  { // post

    enif_release_resource((void*)args->handle);
  });

ASYNC_NIF_DECL(
  lmdb_txn_abort,
  { // struct

      struct lmdb *handle;
  },
  { // pre

      if (!(argc == 1 &&
        enif_get_resource(env, argv[0], lmdb_RESOURCE, (void**)&args->handle))) {
      ASYNC_NIF_RETURN_BADARG();
      }
      if (!args->handle->env)
      ASYNC_NIF_RETURN_BADARG();
      enif_keep_resource((void*)args->handle);
  },
  { // work

      if(args->handle->txn != NULL) {
          mdb_txn_abort(args->handle->txn);
          args->handle->txn = NULL;
          ASYNC_NIF_REPLY(ATOM_OK);
      } else
          ASYNC_NIF_REPLY(enif_make_tuple(env, 2, ATOM_ERROR, ATOM_TXN_NOT_STARTED));
      return;
  },
  { // post

    enif_release_resource((void*)args->handle);
  });

static int lmdb_load(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)
{
    __UNUSED(load_info);

    ErlNifResourceFlags flags = ERL_NIF_RT_CREATE | ERL_NIF_RT_TAKEOVER;

    struct lmdb_priv_data *priv = enif_alloc(sizeof(struct lmdb_priv_data));
    if (!priv)
        return ENOMEM;
    memset(priv, 0, sizeof(struct lmdb_priv_data));

    /* Note: !!! the first element of our priv_data struct *must* be the
       pointer to the async_nif's private data which we set here. */
    ASYNC_NIF_LOAD(lmdb, env, priv->async_nif_priv);
    if (!priv)
        return ENOMEM;
    *priv_data = priv;

    ATOM_ERROR = enif_make_atom(env, "error");
    ATOM_OK = enif_make_atom(env, "ok");
    ATOM_NOT_FOUND = enif_make_atom(env, "not_found");
    ATOM_EXISTS = enif_make_atom(env, "exists");

    ATOM_KEYEXIST = enif_make_atom(env, "key_exist");
    ATOM_NOTFOUND = enif_make_atom(env, "notfound");
    ATOM_CORRUPTED = enif_make_atom(env, "corrupted");
    ATOM_PANIC = enif_make_atom(env, "panic");
    ATOM_VERSION_MISMATCH = enif_make_atom(env, "version_mismatch");
    ATOM_MAP_FULL = enif_make_atom(env, "map_full");
    ATOM_DBS_FULL = enif_make_atom(env, "dbs_full");
    ATOM_READERS_FULL = enif_make_atom(env, "readers_full");
    ATOM_TLS_FULL = enif_make_atom(env, "tls_full");
    ATOM_TXN_FULL = enif_make_atom(env, "txn_full");
    ATOM_CURSOR_FULL = enif_make_atom(env, "cursor_full");
    ATOM_PAGE_FULL = enif_make_atom(env, "page_full");
    ATOM_MAP_RESIZED = enif_make_atom(env, "map_resized");
    ATOM_INCOMPATIBLE = enif_make_atom(env, "incompatible");
    ATOM_BAD_RSLOT = enif_make_atom(env, "bad_rslot");

    ATOM_TXN_STARTED = enif_make_atom(env, "txn_started");
    ATOM_TXN_NOT_STARTED = enif_make_atom(env, "txn_not_started");

    lmdb_RESOURCE = enif_open_resource_type(env, NULL, "lmdb_resource",
					    NULL, flags, NULL);
    return (0);
}

static int lmdb_reload(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM info)
{
    __UNUSED(env);
    __UNUSED(priv_data);
    __UNUSED(info);
    return (0); // TODO:
}


static int lmdb_upgrade(ErlNifEnv* env, void** priv_data, void** old_priv, ERL_NIF_TERM load_info)
{
    __UNUSED(env);
    __UNUSED(priv_data);
    __UNUSED(old_priv);
    __UNUSED(load_info);
    ASYNC_NIF_UPGRADE(lmdb, env);
    return (0); // TODO:
}


static void lmdb_unload(ErlNifEnv* env, void* priv_data)
{
    struct lmdb_priv_data *priv = (struct lmdb_priv_data *)priv_data;
    ASYNC_NIF_UNLOAD(lmdb, env, priv->async_nif_priv);
    enif_free(priv);
    return;
}

static ErlNifFunc nif_funcs [] = {
    {"open",        4, lmdb_open},
    {"close",       2, lmdb_close},
    {"put",         4, lmdb_put},
    {"get",         3, lmdb_get},
    {"del",         3, lmdb_del},
    {"update",      4, lmdb_update},
    {"drop",        2, lmdb_drop},

    {"txn_begin",   2, lmdb_txn_begin},
    {"txn_commit",  2, lmdb_txn_commit},
    {"txn_abort",   2, lmdb_txn_abort}/*,

    {"cursor_open",  2, lmdb_cursor_open},
    {"cursor_close", 2, lmdb_cursor_close} */

};

/* driver entry point */
ERL_NIF_INIT(lmdb,
             nif_funcs,
             & lmdb_load,
             & lmdb_reload,
             & lmdb_upgrade,
             & lmdb_unload)