// Snapshot implements the raft.Storage interface.
// Snapshot requires that the replica lock is held.
func (r *Replica) Snapshot() (raftpb.Snapshot, error) {
	// Copy all the data from a consistent RocksDB snapshot into a RaftSnapshotData.
	snap := r.store.NewSnapshot()
	defer snap.Close()
	var snapData roachpb.RaftSnapshotData

	firstIndex, err := r.FirstIndex()
	if err != nil {
		return raftpb.Snapshot{}, err
	}

	// Read the range metadata from the snapshot instead of the members
	// of the Range struct because they might be changed concurrently.
	appliedIndex, err := r.loadAppliedIndexLocked(snap)
	if err != nil {
		return raftpb.Snapshot{}, err
	}

	var desc roachpb.RangeDescriptor
	// We ignore intents on the range descriptor (consistent=false) because we
	// know they cannot be committed yet; operations that modify range
	// descriptors resolve their own intents when they commit.
	ok, err := engine.MVCCGetProto(snap, keys.RangeDescriptorKey(r.mu.desc.StartKey),
		r.store.Clock().Now(), false /* !consistent */, nil, &desc)
	if err != nil {
		return raftpb.Snapshot{}, util.Errorf("failed to get desc: %s", err)
	}
	if !ok {
		return raftpb.Snapshot{}, util.Errorf("couldn't find range descriptor")
	}

	// Store RangeDescriptor as metadata, it will be retrieved by ApplySnapshot()
	snapData.RangeDescriptor = desc

	// Iterate over all the data in the range, including local-only data like
	// the sequence cache.
	iter := newReplicaDataIterator(&desc, snap, true /* !replicatedOnly */)
	defer iter.Close()
	for ; iter.Valid(); iter.Next() {
		key := iter.Key()
		snapData.KV = append(snapData.KV,
			roachpb.RaftSnapshotData_KeyValue{
				Key:       key.Key,
				Value:     iter.Value(),
				Timestamp: key.Timestamp,
			})
	}

	entries, err := r.entries(snap, firstIndex, appliedIndex+1, 0)
	if err != nil {
		return raftpb.Snapshot{}, err
	}
	snapData.LogEntries = entries

	data, err := proto.Marshal(&snapData)
	if err != nil {
		return raftpb.Snapshot{}, err
	}

	// Synthesize our raftpb.ConfState from desc.
	var cs raftpb.ConfState
	for _, rep := range desc.Replicas {
		cs.Nodes = append(cs.Nodes, uint64(rep.ReplicaID))
	}

	term, err := r.Term(appliedIndex)
	if err != nil {
		return raftpb.Snapshot{}, util.Errorf("failed to fetch term of %d: %s", appliedIndex, err)
	}

	return raftpb.Snapshot{
		Data: data,
		Metadata: raftpb.SnapshotMetadata{
			Index:     appliedIndex,
			Term:      term,
			ConfState: cs,
		},
	}, nil
}

func snapshot(
	ctx context.Context,
	snap engine.Reader,
	rangeID roachpb.RangeID,
	eCache *raftEntryCache,
	startKey roachpb.RKey,
) (raftpb.Snapshot, error) {
	start := timeutil.Now()
	var snapData roachpb.RaftSnapshotData

	truncState, err := loadTruncatedState(ctx, snap, rangeID)
	if err != nil {
		return raftpb.Snapshot{}, err
	}
	firstIndex := truncState.Index + 1

	// Read the range metadata from the snapshot instead of the members
	// of the Range struct because they might be changed concurrently.
	appliedIndex, _, err := loadAppliedIndex(ctx, snap, rangeID)
	if err != nil {
		return raftpb.Snapshot{}, err
	}

	var desc roachpb.RangeDescriptor
	// We ignore intents on the range descriptor (consistent=false) because we
	// know they cannot be committed yet; operations that modify range
	// descriptors resolve their own intents when they commit.
	ok, err := engine.MVCCGetProto(ctx, snap, keys.RangeDescriptorKey(startKey),
		hlc.MaxTimestamp, false /* !consistent */, nil, &desc)
	if err != nil {
		return raftpb.Snapshot{}, errors.Errorf("failed to get desc: %s", err)
	}
	if !ok {
		return raftpb.Snapshot{}, errors.Errorf("couldn't find range descriptor")
	}

	// Store RangeDescriptor as metadata, it will be retrieved by ApplySnapshot()
	snapData.RangeDescriptor = desc

	// Iterate over all the data in the range, including local-only data like
	// the sequence cache.
	iter := NewReplicaDataIterator(&desc, snap, true /* replicatedOnly */)
	defer iter.Close()
	var alloc bufalloc.ByteAllocator
	for ; iter.Valid(); iter.Next() {
		var key engine.MVCCKey
		var value []byte
		alloc, key, value = iter.allocIterKeyValue(alloc)
		snapData.KV = append(snapData.KV,
			roachpb.RaftSnapshotData_KeyValue{
				Key:       key.Key,
				Value:     value,
				Timestamp: key.Timestamp,
			})
	}

	endIndex := appliedIndex + 1
	snapData.LogEntries = make([][]byte, 0, endIndex-firstIndex)

	scanFunc := func(kv roachpb.KeyValue) (bool, error) {
		bytes, err := kv.Value.GetBytes()
		if err == nil {
			snapData.LogEntries = append(snapData.LogEntries, bytes)
		}
		return false, err
	}

	if err := iterateEntries(ctx, snap, rangeID, firstIndex, endIndex, scanFunc); err != nil {
		return raftpb.Snapshot{}, err
	}

	data, err := protoutil.Marshal(&snapData)
	if err != nil {
		return raftpb.Snapshot{}, err
	}

	// Synthesize our raftpb.ConfState from desc.
	var cs raftpb.ConfState
	for _, rep := range desc.Replicas {
		cs.Nodes = append(cs.Nodes, uint64(rep.ReplicaID))
	}

	term, err := term(ctx, snap, rangeID, eCache, appliedIndex)
	if err != nil {
		return raftpb.Snapshot{}, errors.Errorf("failed to fetch term of %d: %s", appliedIndex, err)
	}

	log.Infof(ctx, "generated snapshot for range %s at index %d in %s. encoded size=%d, %d KV pairs, %d log entries",
		rangeID, appliedIndex, timeutil.Since(start), len(data), len(snapData.KV), len(snapData.LogEntries))

	return raftpb.Snapshot{
		Data: data,
		Metadata: raftpb.SnapshotMetadata{
			Index:     appliedIndex,
			Term:      term,
			ConfState: cs,
		},
	}, nil
}