// writeInitialState bootstraps a new Raft group (i.e. it is called when we
// bootstrap a Range, or when setting up the right hand side of a split).
// Its main task is to persist a consistent Raft (and associated Replica) state
// which does not start from zero but presupposes a few entries already having
// applied.
// The supplied MVCCStats are used for the Stats field after adjusting for
// persisting the state itself, and the updated stats are returned.
func writeInitialState(
	ctx context.Context, eng engine.ReadWriter, ms enginepb.MVCCStats, desc roachpb.RangeDescriptor,
) (enginepb.MVCCStats, error) {
	var s storagebase.ReplicaState

	s.TruncatedState = &roachpb.RaftTruncatedState{
		Term:  raftInitialLogTerm,
		Index: raftInitialLogIndex,
	}
	s.RaftAppliedIndex = s.TruncatedState.Index
	s.Desc = &roachpb.RangeDescriptor{
		RangeID: desc.RangeID,
	}
	s.Stats = ms

	newMS, err := saveState(ctx, eng, s)
	if err != nil {
		return enginepb.MVCCStats{}, err
	}

	oldHS, err := loadHardState(ctx, eng, desc.RangeID)
	if err != nil {
		return enginepb.MVCCStats{}, err
	}

	if err := synthesizeHardState(ctx, eng, s, oldHS); err != nil {
		return enginepb.MVCCStats{}, err
	}

	if err := setLastIndex(ctx, eng, desc.RangeID, s.TruncatedState.Index); err != nil {
		return enginepb.MVCCStats{}, err
	}

	return newMS, nil
}

// writeInitialState bootstraps a new Raft group (i.e. it is called when we
// bootstrap a Range, or when setting up the right hand side of a split).
// Its main task is to persist a consistent Raft (and associated Replica) state
// which does not start from zero but presupposes a few entries already having
// applied.
// The supplied MVCCStats are used for the Stats field after adjusting for
// persisting the state itself, and the updated stats are returned.
func writeInitialState(
	eng engine.ReadWriter, ms enginepb.MVCCStats, desc roachpb.RangeDescriptor,
) (enginepb.MVCCStats, error) {
	rangeID := desc.RangeID
	var s storagebase.ReplicaState

	s.TruncatedState = &roachpb.RaftTruncatedState{
		Term:  raftInitialLogTerm,
		Index: raftInitialLogIndex,
	}
	s.RaftAppliedIndex = s.TruncatedState.Index
	s.Desc = &roachpb.RangeDescriptor{
		RangeID: rangeID,
	}
	s.Stats = ms

	newMS, err := saveState(eng, s)
	if err != nil {
		return enginepb.MVCCStats{}, err
	}

	if err := updateHardState(eng, s); err != nil {
		return enginepb.MVCCStats{}, err
	}

	if err := setLastIndex(eng, rangeID, s.TruncatedState.Index); err != nil {
		return enginepb.MVCCStats{}, err
	}

	return newMS, nil
}

// writeInitialState bootstraps a new Raft group (i.e. it is called when we
// bootstrap a Range, or when setting up the right hand side of a split).
// Its main task is to persist a consistent Raft (and associated Replica) state
// which does not start from zero but presupposes a few entries already having
// applied.
// The supplied MVCCStats are used for the Stats field after adjusting for
// persisting the state itself, and the updated stats are returned.
func writeInitialState(
	eng engine.ReadWriter, ms enginepb.MVCCStats, desc roachpb.RangeDescriptor,
) (enginepb.MVCCStats, error) {
	rangeID := desc.RangeID
	var s storagebase.ReplicaState

	s.TruncatedState = &roachpb.RaftTruncatedState{
		Term:  raftInitialLogTerm,
		Index: raftInitialLogIndex,
	}
	s.RaftAppliedIndex = s.TruncatedState.Index
	s.Desc = &roachpb.RangeDescriptor{
		RangeID: rangeID,
	}
	s.Stats = ms

	newMS, err := saveState(eng, s)
	if err != nil {
		return enginepb.MVCCStats{}, err
	}

	// Load a potentially existing HardState as we may need to preserve
	// information about cast votes. For example, during a Split for which
	// another node's new right-hand side has contacted us before our left-hand
	// side called in here to create the group.
	oldHS, err := loadHardState(eng, rangeID)
	if err != nil {
		return enginepb.MVCCStats{}, err
	}

	newHS := raftpb.HardState{
		Term:   s.TruncatedState.Term,
		Commit: s.TruncatedState.Index,
	}

	if !raft.IsEmptyHardState(oldHS) {
		if oldHS.Commit > newHS.Commit {
			newHS.Commit = oldHS.Commit
		}
		if oldHS.Term > newHS.Term {
			newHS.Term = oldHS.Term
		}
		newHS.Vote = oldHS.Vote
	}

	if err := setHardState(eng, rangeID, newHS); err != nil {
		return enginepb.MVCCStats{}, err
	}

	if err := setLastIndex(eng, rangeID, s.TruncatedState.Index); err != nil {
		return enginepb.MVCCStats{}, err
	}

	return newMS, nil
}

// loadState loads a ReplicaState from disk. The exception is the Desc field,
// which is updated transactionally, and is populated from the supplied
// RangeDescriptor under the convention that that is the latest committed
// version.
func loadState(
	ctx context.Context,
	reader engine.Reader, desc *roachpb.RangeDescriptor,
) (storagebase.ReplicaState, error) {
	var s storagebase.ReplicaState
	// TODO(tschottdorf): figure out whether this is always synchronous with
	// on-disk state (likely iffy during Split/ChangeReplica triggers).
	s.Desc = protoutil.Clone(desc).(*roachpb.RangeDescriptor)
	// Read the range lease.
	var err error
	if s.Lease, err = loadLease(ctx, reader, desc.RangeID); err != nil {
		return storagebase.ReplicaState{}, err
	}

	if s.Frozen, err = loadFrozenStatus(ctx, reader, desc.RangeID); err != nil {
		return storagebase.ReplicaState{}, err
	}

	if s.GCThreshold, err = loadGCThreshold(ctx, reader, desc.RangeID); err != nil {
		return storagebase.ReplicaState{}, err
	}

	if s.RaftAppliedIndex, s.LeaseAppliedIndex, err = loadAppliedIndex(
		ctx, reader, desc.RangeID,
	); err != nil {
		return storagebase.ReplicaState{}, err
	}

	if s.Stats, err = loadMVCCStats(ctx, reader, desc.RangeID); err != nil {
		return storagebase.ReplicaState{}, err
	}

	// The truncated state should not be optional (i.e. the pointer is
	// pointless), but it is and the migration is not worth it.
	truncState, err := loadTruncatedState(ctx, reader, desc.RangeID)
	if err != nil {
		return storagebase.ReplicaState{}, err
	}
	s.TruncatedState = &truncState

	return s, nil
}