////////////////////////////////////////////////////////////////////////////////
/// 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 Jan Steemann
////////////////////////////////////////////////////////////////////////////////

#ifndef ARANGOD_VOCBASE_REVISION_CACHE_CHUNK_ALLOCATOR_H
#define ARANGOD_VOCBASE_REVISION_CACHE_CHUNK_ALLOCATOR_H 1

#include "Basics/Common.h"
#include "Basics/ConditionVariable.h"
#include "Basics/Mutex.h"
#include "Basics/ReadWriteLock.h"
#include "Basics/Thread.h"
#include "VocBase/RevisionCacheChunk.h"

namespace arangodb {

class CollectionRevisionsCache;
class ReadCache;
class RevisionCacheGCThread;

class RevisionCacheChunkAllocator {
 public:
  RevisionCacheChunkAllocator() = delete;
  RevisionCacheChunkAllocator(RevisionCacheChunkAllocator const&) = delete;
  RevisionCacheChunkAllocator& operator=(RevisionCacheChunkAllocator const&) = delete;

  RevisionCacheChunkAllocator(uint32_t defaultChunkSize, uint64_t totalTargetSize);
  ~RevisionCacheChunkAllocator();
  
 public:

  void startGcThread();
  void stopGcThread();
  void beginShutdown(); 
  
  /// @brief total number of bytes allocated by the cache
  uint64_t totalAllocated();

  /// @brief order a new chunk
  RevisionCacheChunk* orderChunk(CollectionRevisionsCache* collectionCache, uint32_t valueSize, uint32_t chunkSize);

  void returnUsed(ReadCache* cache, RevisionCacheChunk* chunk);

  void removeCollection(ReadCache* cache);

  bool garbageCollect();

 private:
  /// @brief physically delete a chunk
  void deleteChunk(RevisionCacheChunk* chunk) const;

  static constexpr uint32_t blockSize() { return 2048; }

 private:
  // lock for the lists of chunks
  arangodb::basics::ReadWriteLock _chunksLock;

  // completely (or partially unused) chunks that can still be written to
  std::vector<RevisionCacheChunk*> _freeList;

  Mutex _gcLock;

  std::unordered_map<ReadCache*, std::unordered_map<RevisionCacheChunk*, bool>> _fullChunks;

  // default size for new memory chunks
  uint32_t _defaultChunkSize;

  // total target size for all chunks
  uint64_t _totalTargetSize;

  // total number of bytes allocated by chunks
  uint64_t _totalAllocated;

  std::unique_ptr<RevisionCacheGCThread> _gcThread;
};

class RevisionCacheGCThread : public Thread {
 public:
  explicit RevisionCacheGCThread(RevisionCacheChunkAllocator*);
  ~RevisionCacheGCThread() { shutdown(); }

  void beginShutdown() override;
  void signal();
 
 protected:
  void run() override;

 private:
  RevisionCacheChunkAllocator* _allocator;
  basics::ConditionVariable _condition;
};

} // namespace arangodb

#endif