////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
///     http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Max Neunhoeffer
////////////////////////////////////////////////////////////////////////////////

#ifndef ARANGOD_AQL_WALKER_WORKER_H
#define ARANGOD_AQL_WALKER_WORKER_H 1

#include "Basics/Common.h"

namespace arangodb {
namespace aql {

/// @brief functionality to walk an execution plan recursively
template <class T>
class WalkerWorker {
 public:
  WalkerWorker() = default;

  virtual ~WalkerWorker() = default;

  virtual bool before(T*) {
    return false;  // true to abort the whole walking process
  }

  virtual void after(T*) {}

  virtual bool enterSubquery(T*, T*) {  // super, sub
    return true;
  }

  virtual void leaveSubquery(T*,  // super,
                             T*   // sub
  ) {}

#ifdef ARANGODB_ENABLE_FAILURE_TESTS

  bool done(T* en) {
    // make sure a node is only processed once
    if (_done.emplace(en).second) {
      return false;
    }

    // should never happen
    TRI_ASSERT(false);

    return true;
  }

  void reset() { _done.clear(); }

#else

  // this is a no-op in non-failure mode
  bool done(T*) { return false; }

  // this is a no-op in non-failure mode
  void reset() {}

#endif

 private:
#ifdef ARANGODB_ENABLE_FAILURE_TESTS
  arangodb::HashSet<T*> _done;
#endif
};
}  // namespace aql
}  // namespace arangodb

#endif