// 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).

#pragma once

#include "db/dbformat.h"

#include "rocksdb/types.h"

namespace ROCKSDB_NAMESPACE {

struct MetadataReadBounds {

  // The snapshot-visible sequence and the upper bound sampled for this read.

  // Lookups scan through the upper bound but return data only through the

  // snapshot sequence.

  SequenceNumber read_snapshot_seq;

  SequenceNumber newer_version_upper_bound_seq;

};

class ReadCallback {

 public:

  explicit ReadCallback(SequenceNumber last_visible_seq)

      : max_visible_seq_(last_visible_seq) {}

  ReadCallback(SequenceNumber last_visible_seq, SequenceNumber min_uncommitted)

      : max_visible_seq_(last_visible_seq), min_uncommitted_(min_uncommitted) {}

  virtual ~ReadCallback() {}

  // Will be called to see if the seq number visible; if not it moves on to

  // the next seq number.

  virtual bool IsVisibleFullCheck(SequenceNumber seq) = 0;

  inline bool IsVisible(SequenceNumber seq) {

    assert(min_uncommitted_ > 0);

    assert(min_uncommitted_ >= kMinUnCommittedSeq);

    if (seq < min_uncommitted_) {  // handles seq == 0 as well

      assert(seq <= max_visible_seq_);

      return true;

    } else if (max_visible_seq_ < seq) {

      assert(seq != 0);

      return false;

    } else {

      assert(seq != 0);  // already handled in the first if-then clause

      return IsVisibleFullCheck(seq);

    }

  }

  virtual const MetadataReadBounds* GetMetadataReadBounds() const {

    return nullptr;

  }

  virtual bool NeedToTrackNewerVersions(

      const bool* /*per_key_result*/ = nullptr) const {

    return false;

  }

  virtual bool IsNewerVisibleForMetadataRead(SequenceNumber /*seq*/) {

    // Metadata reads with custom visibility callbacks are unsupported. The

    // timestamp callback overrides this method for regular DB reads.

    return false;

  }

  virtual void MaybeRecordNewerVersion(SequenceNumber /*seq*/,

                                       ValueType /*type*/,

                                       bool* /*per_key_result*/ = nullptr) {}

  inline SequenceNumber max_visible_seq() { return max_visible_seq_; }

  inline SequenceNumber min_uncommitted() const { return min_uncommitted_; }

  // Refresh to a more recent visible seq

  virtual void Refresh(SequenceNumber seq) { max_visible_seq_ = seq; }

 protected:

  // The max visible seq, it is usually the snapshot but could be larger if

  // transaction has its own writes written to db.

  SequenceNumber max_visible_seq_ = kMaxSequenceNumber;

  // Any seq less than min_uncommitted_ is committed.

  const SequenceNumber min_uncommitted_ = kMinUnCommittedSeq;

};

}  // namespace ROCKSDB_NAMESPACE