package stmgr

import (
	"context"
	"fmt"
	"sync"

	"github.com/filecoin-project/go-address"
	amt "github.com/filecoin-project/go-amt-ipld/v2"
	"github.com/filecoin-project/lotus/api"
	"github.com/filecoin-project/lotus/chain/actors"
	"github.com/filecoin-project/lotus/chain/state"
	"github.com/filecoin-project/lotus/chain/store"
	"github.com/filecoin-project/lotus/chain/types"
	"github.com/filecoin-project/lotus/chain/vm"
	"github.com/filecoin-project/specs-actors/actors/abi"
	"github.com/filecoin-project/specs-actors/actors/abi/big"
	"github.com/filecoin-project/specs-actors/actors/builtin"
	"github.com/filecoin-project/specs-actors/actors/builtin/market"
	"github.com/filecoin-project/specs-actors/actors/builtin/reward"
	"github.com/filecoin-project/specs-actors/actors/runtime"
	"github.com/filecoin-project/specs-actors/actors/util/adt"
	cbg "github.com/whyrusleeping/cbor-gen"
	"golang.org/x/xerrors"

	bls "github.com/filecoin-project/filecoin-ffi"
	"github.com/ipfs/go-cid"
	hamt "github.com/ipfs/go-hamt-ipld"
	blockstore "github.com/ipfs/go-ipfs-blockstore"
	cbor "github.com/ipfs/go-ipld-cbor"
	logging "github.com/ipfs/go-log/v2"
	"go.opencensus.io/trace"
)

var log = logging.Logger("statemgr")

type StateManager struct {
	cs *store.ChainStore

	stCache  map[string][]cid.Cid
	compWait map[string]chan struct{}
	stlk     sync.Mutex
	newVM    func(cid.Cid, abi.ChainEpoch, vm.Rand, blockstore.Blockstore, runtime.Syscalls) (*vm.VM, error)
}

func NewStateManager(cs *store.ChainStore) *StateManager {
	return &StateManager{
		newVM:    vm.NewVM,
		cs:       cs,
		stCache:  make(map[string][]cid.Cid),
		compWait: make(map[string]chan struct{}),
	}
}

func cidsToKey(cids []cid.Cid) string {
	var out string
	for _, c := range cids {
		out += c.KeyString()
	}
	return out
}

func (sm *StateManager) TipSetState(ctx context.Context, ts *types.TipSet) (st cid.Cid, rec cid.Cid, err error) {
	ctx, span := trace.StartSpan(ctx, "tipSetState")
	defer span.End()
	if span.IsRecordingEvents() {
		span.AddAttributes(trace.StringAttribute("tipset", fmt.Sprint(ts.Cids())))
	}

	ck := cidsToKey(ts.Cids())
	sm.stlk.Lock()
	cw, cwok := sm.compWait[ck]
	if cwok {
		sm.stlk.Unlock()
		span.AddAttributes(trace.BoolAttribute("waited", true))
		select {
		case <-cw:
			sm.stlk.Lock()
		case <-ctx.Done():
			return cid.Undef, cid.Undef, ctx.Err()
		}
	}
	cached, ok := sm.stCache[ck]
	if ok {
		sm.stlk.Unlock()
		span.AddAttributes(trace.BoolAttribute("cache", true))
		return cached[0], cached[1], nil
	}
	ch := make(chan struct{})
	sm.compWait[ck] = ch

	defer func() {
		sm.stlk.Lock()
		delete(sm.compWait, ck)
		if st != cid.Undef {
			sm.stCache[ck] = []cid.Cid{st, rec}
		}
		sm.stlk.Unlock()
		close(ch)
	}()

	sm.stlk.Unlock()

	if ts.Height() == 0 {
		// NB: This is here because the process that executes blocks requires that the
		// block miner reference a valid miner in the state tree. Unless we create some
		// magical genesis miner, this won't work properly, so we short circuit here
		// This avoids the question of 'who gets paid the genesis block reward'
		return ts.Blocks()[0].ParentStateRoot, ts.Blocks()[0].ParentMessageReceipts, nil
	}

	st, rec, err = sm.computeTipSetState(ctx, ts.Blocks(), nil)
	if err != nil {
		return cid.Undef, cid.Undef, err
	}

	return st, rec, nil
}

func (sm *StateManager) ExecutionTrace(ctx context.Context, ts *types.TipSet) (cid.Cid, []*api.InvocResult, error) {
	var trace []*api.InvocResult
	st, _, err := sm.computeTipSetState(ctx, ts.Blocks(), func(mcid cid.Cid, msg *types.Message, ret *vm.ApplyRet) error {
		ir := &api.InvocResult{
			Msg:                msg,
			MsgRct:             &ret.MessageReceipt,
			InternalExecutions: ret.InternalExecutions,
			Duration:           ret.Duration,
		}
		if ret.ActorErr != nil {
			ir.Error = ret.ActorErr.Error()
		}
		trace = append(trace, ir)
		return nil
	})
	if err != nil {
		return cid.Undef, nil, err
	}

	return st, trace, nil
}

type BlockMessages struct {
	Miner         address.Address
	BlsMessages   []types.ChainMsg
	SecpkMessages []types.ChainMsg
	TicketCount   int64
}

type ExecCallback func(cid.Cid, *types.Message, *vm.ApplyRet) error

func (sm *StateManager) ApplyBlocks(ctx context.Context, pstate cid.Cid, bms []BlockMessages, epoch abi.ChainEpoch, r vm.Rand, cb ExecCallback) (cid.Cid, cid.Cid, error) {
	vmi, err := sm.newVM(pstate, epoch, r, sm.cs.Blockstore(), sm.cs.VMSys())
	if err != nil {
		return cid.Undef, cid.Undef, xerrors.Errorf("instantiating VM failed: %w", err)
	}

	var receipts []cbg.CBORMarshaler
	processedMsgs := map[cid.Cid]bool{}
	for _, b := range bms {
		penalty := types.NewInt(0)
		gasReward := big.Zero()

		for _, cm := range append(b.BlsMessages, b.SecpkMessages...) {
			m := cm.VMMessage()
			if _, found := processedMsgs[m.Cid()]; found {
				continue
			}
			r, err := vmi.ApplyMessage(ctx, cm)
			if err != nil {
				return cid.Undef, cid.Undef, err
			}

			receipts = append(receipts, &r.MessageReceipt)
			gasReward = big.Add(gasReward, big.Mul(m.GasPrice, big.NewInt(r.GasUsed)))
			penalty = big.Add(penalty, r.Penalty)

			if cb != nil {
				if err := cb(cm.Cid(), m, r); err != nil {
					return cid.Undef, cid.Undef, err
				}
			}
			processedMsgs[m.Cid()] = true
		}

		var err error
		params, err := actors.SerializeParams(&reward.AwardBlockRewardParams{
			Miner:       b.Miner,
			Penalty:     penalty,
			GasReward:   gasReward,
			TicketCount: 1, // TODO: no longer need ticket count here.
		})
		if err != nil {
			return cid.Undef, cid.Undef, xerrors.Errorf("failed to serialize award params: %w", err)
		}

		sysAct, err := vmi.StateTree().GetActor(builtin.SystemActorAddr)
		if err != nil {
			return cid.Undef, cid.Undef, xerrors.Errorf("failed to get system actor: %w", err)
		}

		rwMsg := &types.Message{
			From:     builtin.SystemActorAddr,
			To:       builtin.RewardActorAddr,
			Nonce:    sysAct.Nonce,
			Value:    types.NewInt(0),
			GasPrice: types.NewInt(0),
			GasLimit: 1 << 30,
			Method:   builtin.MethodsReward.AwardBlockReward,
			Params:   params,
		}
		ret, err := vmi.ApplyImplicitMessage(ctx, rwMsg)
		if err != nil {
			return cid.Undef, cid.Undef, xerrors.Errorf("failed to apply reward message for miner %s: %w", b.Miner, err)
		}
		if cb != nil {
			if err := cb(rwMsg.Cid(), rwMsg, ret); err != nil {
				return cid.Undef, cid.Undef, xerrors.Errorf("callback failed on reward message: %w", err)
			}
		}

		if ret.ExitCode != 0 {
			return cid.Undef, cid.Undef, xerrors.Errorf("reward application message failed (exit %d): %s", ret.ExitCode, ret.ActorErr)
		}

	}

	// TODO: this nonce-getting is a tiny bit ugly
	ca, err := vmi.StateTree().GetActor(builtin.SystemActorAddr)
	if err != nil {
		return cid.Undef, cid.Undef, err
	}

	cronMsg := &types.Message{
		To:       builtin.CronActorAddr,
		From:     builtin.SystemActorAddr,
		Nonce:    ca.Nonce,
		Value:    types.NewInt(0),
		GasPrice: types.NewInt(0),
		GasLimit: 1 << 30, // Make super sure this is never too little
		Method:   builtin.MethodsCron.EpochTick,
		Params:   nil,
	}
	ret, err := vmi.ApplyImplicitMessage(ctx, cronMsg)
	if err != nil {
		return cid.Undef, cid.Undef, err
	}
	if cb != nil {
		if err := cb(cronMsg.Cid(), cronMsg, ret); err != nil {
			return cid.Undef, cid.Undef, xerrors.Errorf("callback failed on cron message: %w", err)
		}
	}
	if ret.ExitCode != 0 {
		return cid.Undef, cid.Undef, xerrors.Errorf("CheckProofSubmissions exit was non-zero: %d", ret.ExitCode)
	}

	bs := cbor.NewCborStore(sm.cs.Blockstore())
	rectroot, err := amt.FromArray(ctx, bs, receipts)
	if err != nil {
		return cid.Undef, cid.Undef, xerrors.Errorf("failed to build receipts amt: %w", err)
	}

	st, err := vmi.Flush(ctx)
	if err != nil {
		return cid.Undef, cid.Undef, xerrors.Errorf("vm flush failed: %w", err)
	}

	return st, rectroot, nil
}

func (sm *StateManager) computeTipSetState(ctx context.Context, blks []*types.BlockHeader, cb ExecCallback) (cid.Cid, cid.Cid, error) {
	ctx, span := trace.StartSpan(ctx, "computeTipSetState")
	defer span.End()

	for i := 0; i < len(blks); i++ {
		for j := i + 1; j < len(blks); j++ {
			if blks[i].Miner == blks[j].Miner {
				return cid.Undef, cid.Undef,
					xerrors.Errorf("duplicate miner in a tipset (%s %s)",
						blks[i].Miner, blks[j].Miner)
			}
		}
	}

	pstate := blks[0].ParentStateRoot
	if len(blks[0].Parents) > 0 { // don't support forks on genesis
		parent, err := sm.cs.GetBlock(blks[0].Parents[0])
		if err != nil {
			return cid.Undef, cid.Undef, xerrors.Errorf("getting parent block: %w", err)
		}

		pstate, err = sm.handleStateForks(ctx, blks[0].ParentStateRoot, blks[0].Height, parent.Height)
		if err != nil {
			return cid.Undef, cid.Undef, xerrors.Errorf("error handling state forks: %w", err)
		}
	}

	cids := make([]cid.Cid, len(blks))
	for i, v := range blks {
		cids[i] = v.Cid()
	}

	r := store.NewChainRand(sm.cs, cids, blks[0].Height)

	var blkmsgs []BlockMessages
	for _, b := range blks {
		bms, sms, err := sm.cs.MessagesForBlock(b)
		if err != nil {
			return cid.Undef, cid.Undef, xerrors.Errorf("failed to get messages for block: %w", err)
		}

		bm := BlockMessages{
			Miner:         b.Miner,
			BlsMessages:   make([]types.ChainMsg, 0, len(bms)),
			SecpkMessages: make([]types.ChainMsg, 0, len(sms)),
			TicketCount:   1, //int64(len(b.EPostProof.Proofs)), // TODO fix this
		}

		for _, m := range bms {
			bm.BlsMessages = append(bm.BlsMessages, m)
		}

		for _, m := range sms {
			bm.SecpkMessages = append(bm.SecpkMessages, m)
		}

		blkmsgs = append(blkmsgs, bm)
	}

	return sm.ApplyBlocks(ctx, pstate, blkmsgs, blks[0].Height, r, cb)
}

func (sm *StateManager) parentState(ts *types.TipSet) cid.Cid {
	if ts == nil {
		ts = sm.cs.GetHeaviestTipSet()
	}

	return ts.ParentState()
}

func (sm *StateManager) GetActor(addr address.Address, ts *types.TipSet) (*types.Actor, error) {
	cst := cbor.NewCborStore(sm.cs.Blockstore())
	state, err := state.LoadStateTree(cst, sm.parentState(ts))
	if err != nil {
		return nil, xerrors.Errorf("load state tree: %w", err)
	}

	return state.GetActor(addr)
}

func (sm *StateManager) getActorRaw(addr address.Address, st cid.Cid) (*types.Actor, error) {
	cst := cbor.NewCborStore(sm.cs.Blockstore())
	state, err := state.LoadStateTree(cst, st)
	if err != nil {
		return nil, xerrors.Errorf("load state tree: %w", err)
	}

	return state.GetActor(addr)
}

func (sm *StateManager) GetBalance(addr address.Address, ts *types.TipSet) (types.BigInt, error) {
	act, err := sm.GetActor(addr, ts)
	if err != nil {
		if xerrors.Is(err, types.ErrActorNotFound) {
			return types.NewInt(0), nil
		}
		return types.EmptyInt, xerrors.Errorf("get actor: %w", err)
	}

	return act.Balance, nil
}

func (sm *StateManager) ChainStore() *store.ChainStore {
	return sm.cs
}

func (sm *StateManager) LoadActorState(ctx context.Context, a address.Address, out interface{}, ts *types.TipSet) (*types.Actor, error) {
	act, err := sm.GetActor(a, ts)
	if err != nil {
		return nil, err
	}

	cst := cbor.NewCborStore(sm.cs.Blockstore())
	if err := cst.Get(ctx, act.Head, out); err != nil {
		var r cbg.Deferred
		_ = cst.Get(ctx, act.Head, &r)
		log.Errorw("bad actor head", "error", err, "raw", r.Raw, "address", a)

		return nil, err
	}

	return act, nil
}

func (sm *StateManager) LoadActorStateRaw(ctx context.Context, a address.Address, out interface{}, st cid.Cid) (*types.Actor, error) {
	act, err := sm.getActorRaw(a, st)
	if err != nil {
		return nil, err
	}

	cst := cbor.NewCborStore(sm.cs.Blockstore())
	if err := cst.Get(ctx, act.Head, out); err != nil {
		return nil, err
	}

	return act, nil
}

// ResolveToKeyAddress is similar to `vm.ResolveToKeyAddr` but does not allow `Actor` type of addresses.
// Uses the `TipSet` `ts` to generate the VM state.
func (sm *StateManager) ResolveToKeyAddress(ctx context.Context, addr address.Address, ts *types.TipSet) (address.Address, error) {
	switch addr.Protocol() {
	case address.BLS, address.SECP256K1:
		return addr, nil
	case address.Actor:
		return address.Undef, xerrors.New("cannot resolve actor address to key address")
	default:
	}

	if ts == nil {
		ts = sm.cs.GetHeaviestTipSet()
	}

	st, _, err := sm.TipSetState(ctx, ts)
	if err != nil {
		return address.Undef, xerrors.Errorf("resolve address failed to get tipset state: %w", err)
	}

	cst := cbor.NewCborStore(sm.cs.Blockstore())
	tree, err := state.LoadStateTree(cst, st)
	if err != nil {
		return address.Undef, xerrors.Errorf("failed to load state tree")
	}

	return vm.ResolveToKeyAddr(tree, cst, addr)
}

func (sm *StateManager) GetBlsPublicKey(ctx context.Context, addr address.Address, ts *types.TipSet) (pubk bls.PublicKey, err error) {
	kaddr, err := sm.ResolveToKeyAddress(ctx, addr, ts)
	if err != nil {
		return pubk, xerrors.Errorf("failed to resolve address to key address: %w", err)
	}

	if kaddr.Protocol() != address.BLS {
		return pubk, xerrors.Errorf("address must be BLS address to load bls public key")
	}

	copy(pubk[:], kaddr.Payload())
	return pubk, nil
}

func (sm *StateManager) LookupID(ctx context.Context, addr address.Address, ts *types.TipSet) (address.Address, error) {
	cst := cbor.NewCborStore(sm.cs.Blockstore())
	state, err := state.LoadStateTree(cst, sm.parentState(ts))
	if err != nil {
		return address.Undef, xerrors.Errorf("load state tree: %w", err)
	}
	return state.LookupID(addr)
}

func (sm *StateManager) GetReceipt(ctx context.Context, msg cid.Cid, ts *types.TipSet) (*types.MessageReceipt, error) {
	m, err := sm.cs.GetCMessage(msg)
	if err != nil {
		return nil, fmt.Errorf("failed to load message: %w", err)
	}

	r, err := sm.tipsetExecutedMessage(ts, msg, m.VMMessage())
	if err != nil {
		return nil, err
	}

	if r != nil {
		return r, nil
	}

	_, r, err = sm.searchBackForMsg(ctx, ts, m)
	if err != nil {
		return nil, fmt.Errorf("failed to look back through chain for message: %w", err)
	}

	return r, nil
}

func (sm *StateManager) WaitForMessage(ctx context.Context, mcid cid.Cid) (*types.TipSet, *types.MessageReceipt, error) {
	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

	msg, err := sm.cs.GetCMessage(mcid)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to load message: %w", err)
	}

	tsub := sm.cs.SubHeadChanges(ctx)

	head, ok := <-tsub
	if !ok {
		return nil, nil, fmt.Errorf("SubHeadChanges stream was invalid")
	}

	if len(head) != 1 {
		return nil, nil, fmt.Errorf("SubHeadChanges first entry should have been one item")
	}

	if head[0].Type != store.HCCurrent {
		return nil, nil, fmt.Errorf("expected current head on SHC stream (got %s)", head[0].Type)
	}

	r, err := sm.tipsetExecutedMessage(head[0].Val, mcid, msg.VMMessage())
	if err != nil {
		return nil, nil, err
	}

	if r != nil {
		return head[0].Val, r, nil
	}

	var backTs *types.TipSet
	var backRcp *types.MessageReceipt
	backSearchWait := make(chan struct{})
	go func() {
		fts, r, err := sm.searchBackForMsg(ctx, head[0].Val, msg)
		if err != nil {
			log.Warnf("failed to look back through chain for message: %w", err)
			return
		}

		backTs = fts
		backRcp = r
		close(backSearchWait)
	}()

	for {
		select {
		case notif, ok := <-tsub:
			if !ok {
				return nil, nil, ctx.Err()
			}
			for _, val := range notif {
				switch val.Type {
				case store.HCRevert:
					continue
				case store.HCApply:
					r, err := sm.tipsetExecutedMessage(val.Val, mcid, msg.VMMessage())
					if err != nil {
						return nil, nil, err
					}
					if r != nil {
						return val.Val, r, nil
					}
				}
			}
		case <-backSearchWait:
			if backTs != nil {
				return backTs, backRcp, nil
			}
			backSearchWait = nil
		case <-ctx.Done():
			return nil, nil, ctx.Err()
		}
	}
}

func (sm *StateManager) SearchForMessage(ctx context.Context, mcid cid.Cid) (*types.TipSet, *types.MessageReceipt, error) {
	msg, err := sm.cs.GetCMessage(mcid)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to load message: %w", err)
	}

	head := sm.cs.GetHeaviestTipSet()

	r, err := sm.tipsetExecutedMessage(head, mcid, msg.VMMessage())
	if err != nil {
		return nil, nil, err
	}

	if r != nil {
		return head, r, nil
	}

	fts, r, err := sm.searchBackForMsg(ctx, head, msg)

	if err != nil {
		log.Warnf("failed to look back through chain for message %s", mcid)
		return nil, nil, err
	}

	if fts == nil {
		return nil, nil, nil
	}

	return fts, r, nil
}

func (sm *StateManager) searchBackForMsg(ctx context.Context, from *types.TipSet, m types.ChainMsg) (*types.TipSet, *types.MessageReceipt, error) {

	cur := from
	for {
		if cur.Height() == 0 {
			// it ain't here!
			return nil, nil, nil
		}

		select {
		case <-ctx.Done():
			return nil, nil, nil
		default:
		}

		act, err := sm.GetActor(m.VMMessage().From, cur)
		if err != nil {
			return nil, nil, err
		}

		if act.Nonce < m.VMMessage().Nonce {
			// nonce on chain is before message nonce we're looking for, its
			// not going to be here
			return nil, nil, nil
		}

		ts, err := sm.cs.LoadTipSet(cur.Parents())
		if err != nil {
			return nil, nil, fmt.Errorf("failed to load tipset during msg wait searchback: %w", err)
		}

		r, err := sm.tipsetExecutedMessage(ts, m.Cid(), m.VMMessage())
		if err != nil {
			return nil, nil, fmt.Errorf("checking for message execution during lookback: %w", err)
		}

		if r != nil {
			return ts, r, nil
		}

		cur = ts
	}
}

func (sm *StateManager) tipsetExecutedMessage(ts *types.TipSet, msg cid.Cid, vmm *types.Message) (*types.MessageReceipt, error) {
	// The genesis block did not execute any messages
	if ts.Height() == 0 {
		return nil, nil
	}

	pts, err := sm.cs.LoadTipSet(ts.Parents())
	if err != nil {
		return nil, err
	}

	cm, err := sm.cs.MessagesForTipset(pts)
	if err != nil {
		return nil, err
	}

	for ii := range cm {
		// iterate in reverse because we going backwards through the chain
		i := len(cm) - ii - 1
		m := cm[i]

		if m.VMMessage().From == vmm.From { // cheaper to just check origin first
			if m.VMMessage().Nonce == vmm.Nonce {
				if m.Cid() == msg {
					return sm.cs.GetParentReceipt(ts.Blocks()[0], i)
				}

				// this should be that message
				return nil, xerrors.Errorf("found message with equal nonce as the one we are looking for (F:%s n %d, TS: %s n%d)",
					msg, vmm.Nonce, m.Cid(), m.VMMessage().Nonce)
			}
			if m.VMMessage().Nonce < vmm.Nonce {
				return nil, nil // don't bother looking further
			}
		}
	}

	return nil, nil
}

func (sm *StateManager) ListAllActors(ctx context.Context, ts *types.TipSet) ([]address.Address, error) {
	if ts == nil {
		ts = sm.cs.GetHeaviestTipSet()
	}
	st, _, err := sm.TipSetState(ctx, ts)
	if err != nil {
		return nil, err
	}

	cst := cbor.NewCborStore(sm.cs.Blockstore())
	r, err := hamt.LoadNode(ctx, cst, st, hamt.UseTreeBitWidth(5))
	if err != nil {
		return nil, err
	}

	var out []address.Address
	err = r.ForEach(ctx, func(k string, val interface{}) error {
		addr, err := address.NewFromBytes([]byte(k))
		if err != nil {
			return xerrors.Errorf("address in state tree was not valid: %w", err)
		}
		out = append(out, addr)
		return nil
	})
	if err != nil {
		return nil, err
	}

	return out, nil
}

func (sm *StateManager) MarketBalance(ctx context.Context, addr address.Address, ts *types.TipSet) (api.MarketBalance, error) {
	var state market.State
	_, err := sm.LoadActorState(ctx, builtin.StorageMarketActorAddr, &state, ts)
	if err != nil {
		return api.MarketBalance{}, err
	}

	addr, err = sm.LookupID(ctx, addr, ts)
	if err != nil {
		return api.MarketBalance{}, err
	}

	var out api.MarketBalance

	et, err := adt.AsBalanceTable(sm.cs.Store(ctx), state.EscrowTable)
	if err != nil {
		return api.MarketBalance{}, err
	}
	ehas, err := et.Has(addr)
	if err != nil {
		return api.MarketBalance{}, err
	}
	if ehas {
		out.Escrow, err = et.Get(addr)
		if err != nil {
			return api.MarketBalance{}, xerrors.Errorf("getting escrow balance: %w", err)
		}
	} else {
		out.Escrow = big.Zero()
	}

	lt, err := adt.AsBalanceTable(sm.cs.Store(ctx), state.LockedTable)
	if err != nil {
		return api.MarketBalance{}, err
	}
	lhas, err := lt.Has(addr)
	if err != nil {
		return api.MarketBalance{}, err
	}
	if lhas {
		out.Locked, err = lt.Get(addr)
		if err != nil {
			return api.MarketBalance{}, xerrors.Errorf("getting locked balance: %w", err)
		}
	} else {
		out.Locked = big.Zero()
	}

	return out, nil
}

func (sm *StateManager) ValidateChain(ctx context.Context, ts *types.TipSet) error {
	tschain := []*types.TipSet{ts}
	for ts.Height() != 0 {
		next, err := sm.cs.LoadTipSet(ts.Parents())
		if err != nil {
			return err
		}

		tschain = append(tschain, next)
		ts = next
	}

	lastState := tschain[len(tschain)-1].ParentState()
	for i := len(tschain) - 1; i >= 0; i-- {
		cur := tschain[i]
		log.Infof("computing state (height: %d, ts=%s)", cur.Height(), cur.Cids())
		if cur.ParentState() != lastState {
			return xerrors.Errorf("tipset chain had state mismatch at height %d", cur.Height())
		}
		st, _, err := sm.TipSetState(ctx, cur)
		if err != nil {
			return err
		}
		lastState = st
	}

	return nil
}

func (sm *StateManager) SetVMConstructor(nvm func(cid.Cid, abi.ChainEpoch, vm.Rand, blockstore.Blockstore, runtime.Syscalls) (*vm.VM, error)) {
	sm.newVM = nvm
}