// Copyright (c) 2011 The LevelDB Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file. See the AUTHORS file for names of contributors.

#ifndef STORAGE_LEVELDB_DB_MEMTABLE_H_

#define STORAGE_LEVELDB_DB_MEMTABLE_H_

#include <string>

#include "db/dbformat.h"

#include "db/skiplist.h"

#include "leveldb/db.h"

#include "util/arena.h"

namespace leveldb {

class InternalKeyComparator;

class MemTableIterator;

class MemTable {

 public:

  // MemTables are reference counted.  The initial reference count

  // is zero and the caller must call Ref() at least once.

  explicit MemTable(const InternalKeyComparator& comparator);

  MemTable(const MemTable&) = delete;

  MemTable& operator=(const MemTable&) = delete;

  // Increase reference count.

  void Ref() { ++refs_; }

  // Drop reference count.  Delete if no more references exist.

  void Unref() {

    --refs_;

    assert(refs_ >= 0);

    if (refs_ <= 0) {

      delete this;

    }

  }

  // Returns an estimate of the number of bytes of data in use by this

  // data structure. It is safe to call when MemTable is being modified.

  size_t ApproximateMemoryUsage();

  // Return an iterator that yields the contents of the memtable.

  //

  // The caller must ensure that the underlying MemTable remains live

  // while the returned iterator is live.  The keys returned by this

  // iterator are internal keys encoded by AppendInternalKey in the

  // db/format.{h,cc} module.

  Iterator* NewIterator();

  // Add an entry into memtable that maps key to value at the

  // specified sequence number and with the specified type.

  // Typically value will be empty if type==kTypeDeletion.

  void Add(SequenceNumber seq, ValueType type, const Slice& key,

           const Slice& value);

  // If memtable contains a value for key, store it in *value and return true.

  // If memtable contains a deletion for key, store a NotFound() error

  // in *status and return true.

  // Else, return false.

  bool Get(const LookupKey& key, std::string* value, Status* s);

 private:

  friend class MemTableIterator;

  friend class MemTableBackwardIterator;

  struct KeyComparator {

    const InternalKeyComparator comparator;

    explicit KeyComparator(const InternalKeyComparator& c) : comparator(c) {}

    int operator()(const char* a, const char* b) const;

  };

  typedef SkipList<const char*, KeyComparator> Table;

  ~MemTable();  // Private since only Unref() should be used to delete it

  KeyComparator comparator_;

  int refs_;

  Arena arena_;

  Table table_;

};

}  // namespace leveldb

#endif  // STORAGE_LEVELDB_DB_MEMTABLE_H_