#include <lmdb.h>
#include <iostream>
#include <cstring>

using namespace std;

class mdb_exception : public exception {
  const char *msg;
public:
  inline explicit mdb_exception(int rc) {
    msg = mdb_strerror(rc);
  }
  inline const char *what() const noexcept {
    return msg;
  }
};

inline int C(int rc) {
  if (rc != 0 && rc != MDB_NOTFOUND) {
    throw mdb_exception(rc);
  }
  return rc;
}

inline void print(const MDB_val &key, const MDB_val &data) {
  cout << "---> key: " << string(static_cast<char*>(key.mv_data), key.mv_size / sizeof(char)) << endl;
  cout << "---> data: " << string(static_cast<char*>(data.mv_data), data.mv_size / sizeof(char)) << endl;
}

int main() {
  MDB_val key, data;
  MDB_env *env;
  MDB_dbi dbi;
  MDB_txn *txn;
  MDB_cursor *cursor;

  // test data
  unsigned testN = 6;
  const char* testKeys[] = { "a", "b", "c", "e", "f", "g" };
  const char* testData[] = { "helló_1", "wőúéáűrld_2", "42_3", "hello_4", "world_5", "42_6"  };

  // set up env
  C(mdb_env_create(&env));
  C(mdb_env_set_maxdbs(env, 10));
  C(mdb_env_open(env, "./testdata", 0, 0644));

  // ------ open a clean dbi + fill up with test data

  // begin a txn
  C(mdb_txn_begin(env, nullptr, 0, &txn));

  // ensure there is an empty dbi
  C(mdb_dbi_open(txn, "my_test_data", MDB_CREATE, &dbi));
  C(mdb_drop(txn, dbi, 1));
  C(mdb_dbi_open(txn, "my_test_data", MDB_CREATE, &dbi));

  // fill up with some data
  for (unsigned i = 0; i < testN; i++) {
    key.mv_data = const_cast<char*>(testKeys[i]);
    key.mv_size = sizeof(char) * strlen(testKeys[i]);
    data.mv_data = const_cast<char*>(testData[i]);
    data.mv_size = sizeof(char) * strlen(testData[i]);

    mdb_put(txn, dbi, &key, &data, 0);
  }

  // commit the txn
  C(mdb_txn_commit(txn));

  // ------ use a cursor

  // begin a txn + cursor
  C(mdb_txn_begin(env, nullptr, 0, &txn));
  C(mdb_cursor_open(txn, dbi, &cursor));

  // mess with the stuff
  cout << "first (expected a)" << endl;
  C(mdb_cursor_get(cursor, &key, &data, MDB_FIRST));
  C(mdb_cursor_get(cursor, &key, &data, MDB_GET_CURRENT));
  print(key, data);

  cout << "next (expected b)" << endl;
  C(mdb_cursor_get(cursor, &key, &data, MDB_NEXT));
  C(mdb_cursor_get(cursor, &key, &data, MDB_GET_CURRENT));
  print(key, data);

  cout << "next (expected c)" << endl;
  C(mdb_cursor_get(cursor, &key, &data, MDB_NEXT));
  C(mdb_cursor_get(cursor, &key, &data, MDB_GET_CURRENT));
  print(key, data);

  cout << "next (expected e)" << endl;
  C(mdb_cursor_get(cursor, &key, &data, MDB_NEXT));
  C(mdb_cursor_get(cursor, &key, &data, MDB_GET_CURRENT));
  print(key, data);

  cout << "prev (expected c)" << endl;
  C(mdb_cursor_get(cursor, &key, &data, MDB_PREV));
  C(mdb_cursor_get(cursor, &key, &data, MDB_GET_CURRENT));
  print(key, data);

  cout << "last (expected g)" << endl;
  C(mdb_cursor_get(cursor, &key, &data, MDB_LAST));
  C(mdb_cursor_get(cursor, &key, &data, MDB_GET_CURRENT));
  print(key, data);

  // oops
  mdb_dbi_close(env, dbi);

  cout << "go to key b (expected b)" << endl;
  key.mv_data = (void*) "b";
  key.mv_size = sizeof(char);
  C(mdb_cursor_get(cursor, &key, &data, MDB_SET));
  C(mdb_cursor_get(cursor, &key, &data, MDB_GET_CURRENT));
  print(key, data);

  cout << "go to key d (expected e)" << endl;
  key.mv_data = (void*) "d";
  key.mv_size = sizeof(char);
  C(mdb_cursor_get(cursor, &key, &data, MDB_SET_RANGE));
  C(mdb_cursor_get(cursor, &key, &data, MDB_GET_CURRENT));
  print(key, data);

  cout << "del (expected f)" << endl;
  C(mdb_cursor_del(cursor, 0));
  C(mdb_cursor_get(cursor, &key, &data, MDB_GET_CURRENT));
  print(key, data);

  // now go through all keys
  cout << "---------------------------------" << endl;
  C(mdb_cursor_get(cursor, &key, &data, MDB_FIRST));
  do {
    print(key, data);
  } while (C(mdb_cursor_get(cursor, &key, &data, MDB_NEXT)) == 0);

  // close cursor + commit the txn
  mdb_cursor_close(cursor);
  C(mdb_txn_commit(txn));

  // close dbi & env
  mdb_dbi_close(env, dbi);
  mdb_env_close(env);

  return 0;
}