// Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).
// 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.

#pragma once

#include <map>
#include <string>

#include "rocksdb/statistics.h"
#include "rocksdb/status.h"

namespace rocksdb {

class DBImpl;

// StatsHistoryIterator is the main interface for users to programmatically
// access statistics snapshots that was automatically stored by RocksDB.
// Depending on options, the stats can be in memory or on disk.
// The stats snapshots are indexed by time that they were recorded, and each
// stats snapshot contains individual stat name and value at the time of
// recording.
// Example:
//   std::unique_ptr<StatsHistoryIterator> stats_iter;
//   Status s = db->GetStatsHistory(0 /* start_time */,
//                                  env->NowMicros() /* end_time*/,
//                                  &stats_iter);
//   if (s.ok) {
//     for (; stats_iter->Valid(); stats_iter->Next()) {
//       uint64_t stats_time = stats_iter->GetStatsTime();
//       const std::map<std::string, uint64_t>& stats_map =
//           stats_iter->GetStatsMap();
//       process(stats_time, stats_map);
//     }
//   }
class StatsHistoryIterator {
 public:
  StatsHistoryIterator() {}
  virtual ~StatsHistoryIterator() {}

  virtual bool Valid() const = 0;

  // Moves to the next stats history record.  After this call, Valid() is
  // true iff the iterator was not positioned at the last entry in the source.
  // REQUIRES: Valid()
  virtual void Next() = 0;

  // Return the time stamp (in seconds) when stats history is recorded.
  // REQUIRES: Valid()
  virtual uint64_t GetStatsTime() const = 0;

  virtual int GetFormatVersion() const { return -1; }

  // Return the current stats history as an std::map which specifies the
  // mapping from stats name to stats value . The underlying storage
  // for the returned map is valid only until the next modification of
  // the iterator.
  // REQUIRES: Valid()
  virtual const std::map<std::string, uint64_t>& GetStatsMap() const = 0;

  // If an error has occurred, return it.  Else return an ok status.
  virtual Status status() const = 0;
};

}  // namespace rocksdb
