package paychmgr

import (
	"bytes"
	"context"
	"fmt"

	"github.com/ipfs/go-cid"

	"github.com/filecoin-project/go-address"
	cborutil "github.com/filecoin-project/go-cbor-util"
	"github.com/filecoin-project/lotus/chain/actors"
	"github.com/filecoin-project/lotus/chain/types"
	"github.com/filecoin-project/lotus/lib/sigs"
	"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/account"
	"github.com/filecoin-project/specs-actors/actors/builtin/paych"
	xerrors "golang.org/x/xerrors"
)

// channelAccessor is used to simplify locking when accessing a channel
type channelAccessor struct {
	// waitCtx is used by processes that wait for things to be confirmed
	// on chain
	waitCtx       context.Context
	sm            StateManagerApi
	sa            *stateAccessor
	api           paychApi
	store         *Store
	lk            *channelLock
	fundsReqQueue []*fundsReq
	msgListeners  msgListeners
}

func newChannelAccessor(pm *Manager) *channelAccessor {
	return &channelAccessor{
		lk:      &channelLock{globalLock: &pm.lk},
		sm:      pm.sm,
		sa:      &stateAccessor{sm: pm.sm},
		api:     pm.pchapi,
		store:   pm.store,
		waitCtx: pm.ctx,
	}
}

func (ca *channelAccessor) getChannelInfo(addr address.Address) (*ChannelInfo, error) {
	ca.lk.Lock()
	defer ca.lk.Unlock()

	return ca.store.ByAddress(addr)
}

func (ca *channelAccessor) checkVoucherValid(ctx context.Context, ch address.Address, sv *paych.SignedVoucher) (map[uint64]*paych.LaneState, error) {
	ca.lk.Lock()
	defer ca.lk.Unlock()

	return ca.checkVoucherValidUnlocked(ctx, ch, sv)
}

func (ca *channelAccessor) checkVoucherValidUnlocked(ctx context.Context, ch address.Address, sv *paych.SignedVoucher) (map[uint64]*paych.LaneState, error) {
	if sv.ChannelAddr != ch {
		return nil, xerrors.Errorf("voucher ChannelAddr doesn't match channel address, got %s, expected %s", sv.ChannelAddr, ch)
	}

	act, pchState, err := ca.sa.loadPaychState(ctx, ch)
	if err != nil {
		return nil, err
	}

	var actState account.State
	_, err = ca.sm.LoadActorState(ctx, pchState.From, &actState, nil)
	if err != nil {
		return nil, err
	}
	from := actState.Address

	// verify signature
	vb, err := sv.SigningBytes()
	if err != nil {
		return nil, err
	}

	// TODO: technically, either party may create and sign a voucher.
	// However, for now, we only accept them from the channel creator.
	// More complex handling logic can be added later
	if err := sigs.Verify(sv.Signature, from, vb); err != nil {
		return nil, err
	}

	// Check the voucher against the highest known voucher nonce / value
	laneStates, err := ca.laneState(pchState, ch)
	if err != nil {
		return nil, err
	}

	// If the new voucher nonce value is less than the highest known
	// nonce for the lane
	ls, lsExists := laneStates[sv.Lane]
	if lsExists && sv.Nonce <= ls.Nonce {
		return nil, fmt.Errorf("nonce too low")
	}

	// If the voucher amount is less than the highest known voucher amount
	if lsExists && sv.Amount.LessThanEqual(ls.Redeemed) {
		return nil, fmt.Errorf("voucher amount is lower than amount for voucher with lower nonce")
	}

	// Total redeemed is the total redeemed amount for all lanes, including
	// the new voucher
	// eg
	//
	// lane 1 redeemed:            3
	// lane 2 redeemed:            2
	// voucher for lane 1:         5
	//
	// Voucher supersedes lane 1 redeemed, therefore
	// effective lane 1 redeemed:  5
	//
	// lane 1:  5
	// lane 2:  2
	//          -
	// total:   7
	totalRedeemed, err := ca.totalRedeemedWithVoucher(laneStates, sv)
	if err != nil {
		return nil, err
	}

	// Total required balance = total redeemed + toSend
	// Must not exceed actor balance
	newTotal := types.BigAdd(totalRedeemed, pchState.ToSend)
	if act.Balance.LessThan(newTotal) {
		return nil, fmt.Errorf("not enough funds in channel to cover voucher")
	}

	if len(sv.Merges) != 0 {
		return nil, fmt.Errorf("dont currently support paych lane merges")
	}

	return laneStates, nil
}

func (ca *channelAccessor) checkVoucherSpendable(ctx context.Context, ch address.Address, sv *paych.SignedVoucher, secret []byte, proof []byte) (bool, error) {
	ca.lk.Lock()
	defer ca.lk.Unlock()

	recipient, err := ca.getPaychRecipient(ctx, ch)
	if err != nil {
		return false, err
	}

	if sv.Extra != nil && proof == nil {
		known, err := ca.store.VouchersForPaych(ch)
		if err != nil {
			return false, err
		}

		for _, v := range known {
			eq, err := cborutil.Equals(v.Voucher, sv)
			if err != nil {
				return false, err
			}
			if v.Proof != nil && eq {
				log.Info("CheckVoucherSpendable: using stored proof")
				proof = v.Proof
				break
			}
		}
		if proof == nil {
			log.Warn("CheckVoucherSpendable: nil proof for voucher with validation")
		}
	}

	enc, err := actors.SerializeParams(&paych.UpdateChannelStateParams{
		Sv:     *sv,
		Secret: secret,
		Proof:  proof,
	})
	if err != nil {
		return false, err
	}

	ret, err := ca.sm.Call(ctx, &types.Message{
		From:   recipient,
		To:     ch,
		Method: builtin.MethodsPaych.UpdateChannelState,
		Params: enc,
	}, nil)
	if err != nil {
		return false, err
	}

	if ret.MsgRct.ExitCode != 0 {
		return false, nil
	}

	return true, nil
}

func (ca *channelAccessor) getPaychRecipient(ctx context.Context, ch address.Address) (address.Address, error) {
	var state paych.State
	if _, err := ca.sm.LoadActorState(ctx, ch, &state, nil); err != nil {
		return address.Address{}, err
	}

	return state.To, nil
}

func (ca *channelAccessor) addVoucher(ctx context.Context, ch address.Address, sv *paych.SignedVoucher, proof []byte, minDelta types.BigInt) (types.BigInt, error) {
	ca.lk.Lock()
	defer ca.lk.Unlock()

	ci, err := ca.store.ByAddress(ch)
	if err != nil {
		return types.BigInt{}, err
	}

	// Check if the voucher has already been added
	for i, v := range ci.Vouchers {
		eq, err := cborutil.Equals(sv, v.Voucher)
		if err != nil {
			return types.BigInt{}, err
		}
		if !eq {
			continue
		}

		// This is a duplicate voucher.
		// Update the proof on the existing voucher
		if len(proof) > 0 && !bytes.Equal(v.Proof, proof) {
			log.Warnf("AddVoucher: adding proof to stored voucher")
			ci.Vouchers[i] = &VoucherInfo{
				Voucher: v.Voucher,
				Proof:   proof,
			}

			return types.NewInt(0), ca.store.putChannelInfo(ci)
		}

		// Otherwise just ignore the duplicate voucher
		log.Warnf("AddVoucher: voucher re-added with matching proof")
		return types.NewInt(0), nil
	}

	// Check voucher validity
	laneStates, err := ca.checkVoucherValidUnlocked(ctx, ch, sv)
	if err != nil {
		return types.NewInt(0), err
	}

	// The change in value is the delta between the voucher amount and
	// the highest previous voucher amount for the lane
	laneState, exists := laneStates[sv.Lane]
	redeemed := big.NewInt(0)
	if exists {
		redeemed = laneState.Redeemed
	}

	delta := types.BigSub(sv.Amount, redeemed)
	if minDelta.GreaterThan(delta) {
		return delta, xerrors.Errorf("addVoucher: supplied token amount too low; minD=%s, D=%s; laneAmt=%s; v.Amt=%s", minDelta, delta, redeemed, sv.Amount)
	}

	ci.Vouchers = append(ci.Vouchers, &VoucherInfo{
		Voucher: sv,
		Proof:   proof,
	})

	if ci.NextLane <= sv.Lane {
		ci.NextLane = sv.Lane + 1
	}

	return delta, ca.store.putChannelInfo(ci)
}

func (ca *channelAccessor) allocateLane(ch address.Address) (uint64, error) {
	ca.lk.Lock()
	defer ca.lk.Unlock()

	// TODO: should this take into account lane state?
	return ca.store.AllocateLane(ch)
}

func (ca *channelAccessor) listVouchers(ctx context.Context, ch address.Address) ([]*VoucherInfo, error) {
	ca.lk.Lock()
	defer ca.lk.Unlock()

	// TODO: just having a passthrough method like this feels odd. Seems like
	// there should be some filtering we're doing here
	return ca.store.VouchersForPaych(ch)
}

func (ca *channelAccessor) nextNonceForLane(ctx context.Context, ch address.Address, lane uint64) (uint64, error) {
	ca.lk.Lock()
	defer ca.lk.Unlock()

	// TODO: should this take into account lane state?
	vouchers, err := ca.store.VouchersForPaych(ch)
	if err != nil {
		return 0, err
	}

	var maxnonce uint64
	for _, v := range vouchers {
		if v.Voucher.Lane == lane {
			if v.Voucher.Nonce > maxnonce {
				maxnonce = v.Voucher.Nonce
			}
		}
	}

	return maxnonce + 1, nil
}

// laneState gets the LaneStates from chain, then applies all vouchers in
// the data store over the chain state
func (ca *channelAccessor) laneState(state *paych.State, ch address.Address) (map[uint64]*paych.LaneState, error) {
	// TODO: we probably want to call UpdateChannelState with all vouchers to be fully correct
	//  (but technically dont't need to)
	laneStates := make(map[uint64]*paych.LaneState, len(state.LaneStates))

	// Get the lane state from the chain
	for _, laneState := range state.LaneStates {
		laneStates[laneState.ID] = laneState
	}

	// Apply locally stored vouchers
	vouchers, err := ca.store.VouchersForPaych(ch)
	if err != nil && err != ErrChannelNotTracked {
		return nil, err
	}

	for _, v := range vouchers {
		for range v.Voucher.Merges {
			return nil, xerrors.Errorf("paych merges not handled yet")
		}

		// If there's a voucher for a lane that isn't in chain state just
		// create it
		ls, ok := laneStates[v.Voucher.Lane]
		if !ok {
			ls = &paych.LaneState{
				ID:       v.Voucher.Lane,
				Redeemed: types.NewInt(0),
				Nonce:    0,
			}
			laneStates[v.Voucher.Lane] = ls
		}

		if v.Voucher.Nonce < ls.Nonce {
			continue
		}

		ls.Nonce = v.Voucher.Nonce
		ls.Redeemed = v.Voucher.Amount
	}

	return laneStates, nil
}

// Get the total redeemed amount across all lanes, after applying the voucher
func (ca *channelAccessor) totalRedeemedWithVoucher(laneStates map[uint64]*paych.LaneState, sv *paych.SignedVoucher) (big.Int, error) {
	// TODO: merges
	if len(sv.Merges) != 0 {
		return big.Int{}, xerrors.Errorf("dont currently support paych lane merges")
	}

	total := big.NewInt(0)
	for _, ls := range laneStates {
		total = big.Add(total, ls.Redeemed)
	}

	lane, ok := laneStates[sv.Lane]
	if ok {
		// If the voucher is for an existing lane, and the voucher nonce
		// and is higher than the lane nonce
		if sv.Nonce > lane.Nonce {
			// Add the delta between the redeemed amount and the voucher
			// amount to the total
			delta := big.Sub(sv.Amount, lane.Redeemed)
			total = big.Add(total, delta)
		}
	} else {
		// If the voucher is *not* for an existing lane, just add its
		// value (implicitly a new lane will be created for the voucher)
		total = big.Add(total, sv.Amount)
	}

	return total, nil
}

func (ca *channelAccessor) settle(ctx context.Context, ch address.Address) (cid.Cid, error) {
	ca.lk.Lock()
	defer ca.lk.Unlock()

	ci, err := ca.store.ByAddress(ch)
	if err != nil {
		return cid.Undef, err
	}

	msg := &types.Message{
		To:     ch,
		From:   ci.Control,
		Value:  types.NewInt(0),
		Method: builtin.MethodsPaych.Settle,
	}
	smgs, err := ca.api.MpoolPushMessage(ctx, msg)
	if err != nil {
		return cid.Undef, err
	}

	ci.Settling = true
	err = ca.store.putChannelInfo(ci)
	if err != nil {
		log.Errorf("Error marking channel as settled: %s", err)
	}

	return smgs.Cid(), err
}