package miner

import (
	"bytes"
	"context"
	"crypto/rand"
	"encoding/binary"
	"fmt"
	"sync"
	"time"

	"github.com/filecoin-project/go-address"
	"github.com/filecoin-project/specs-actors/actors/abi"
	"github.com/filecoin-project/specs-actors/actors/crypto"
	lru "github.com/hashicorp/golang-lru"

	"github.com/filecoin-project/lotus/api"
	"github.com/filecoin-project/lotus/build"
	"github.com/filecoin-project/lotus/chain/gen"
	"github.com/filecoin-project/lotus/chain/store"
	"github.com/filecoin-project/lotus/chain/types"

	logging "github.com/ipfs/go-log/v2"
	"go.opencensus.io/trace"
	"golang.org/x/xerrors"
)

var log = logging.Logger("miner")

// returns a callback reporting whether we mined a blocks in this round
type waitFunc func(ctx context.Context, baseTime uint64) (func(bool, error), abi.ChainEpoch, error)

func randTimeOffset(width time.Duration) time.Duration {
	buf := make([]byte, 8)
	rand.Reader.Read(buf)
	val := time.Duration(binary.BigEndian.Uint64(buf) % uint64(width))

	return val - (width / 2)
}

func NewMiner(api api.FullNode, epp gen.WinningPoStProver, addr address.Address) *Miner {
	arc, err := lru.NewARC(10000)
	if err != nil {
		panic(err)
	}

	return &Miner{
		api:     api,
		epp:     epp,
		address: addr,
		waitFunc: func(ctx context.Context, baseTime uint64) (func(bool, error), abi.ChainEpoch, error) {
			// Wait around for half the block time in case other parents come in
			deadline := baseTime + build.PropagationDelaySecs
			baseT := time.Unix(int64(deadline), 0)

			baseT = baseT.Add(randTimeOffset(time.Second))

			build.Clock.Sleep(build.Clock.Until(baseT))

			return func(bool, error) {}, 0, nil
		},
		minedBlockHeights: arc,
	}
}

type Miner struct {
	api api.FullNode

	epp gen.WinningPoStProver

	lk       sync.Mutex
	address  address.Address
	stop     chan struct{}
	stopping chan struct{}

	waitFunc waitFunc

	lastWork *MiningBase

	minedBlockHeights *lru.ARCCache
}

func (m *Miner) Address() address.Address {
	m.lk.Lock()
	defer m.lk.Unlock()

	return m.address
}

func (m *Miner) Start(ctx context.Context) error {
	m.lk.Lock()
	defer m.lk.Unlock()
	if m.stop != nil {
		return fmt.Errorf("miner already started")
	}
	m.stop = make(chan struct{})
	go m.mine(context.TODO())
	return nil
}

func (m *Miner) Stop(ctx context.Context) error {
	m.lk.Lock()

	m.stopping = make(chan struct{})
	stopping := m.stopping
	close(m.stop)

	m.lk.Unlock()

	select {
	case <-stopping:
		return nil
	case <-ctx.Done():
		return ctx.Err()
	}
}

func (m *Miner) niceSleep(d time.Duration) bool {
	select {
	case <-build.Clock.After(d):
		return true
	case <-m.stop:
		return false
	}
}

func (m *Miner) mine(ctx context.Context) {
	ctx, span := trace.StartSpan(ctx, "/mine")
	defer span.End()

	var lastBase MiningBase

	for {
		select {
		case <-m.stop:
			stopping := m.stopping
			m.stop = nil
			m.stopping = nil
			close(stopping)
			return

		default:
		}

		prebase, err := m.GetBestMiningCandidate(ctx)
		if err != nil {
			log.Errorf("failed to get best mining candidate: %s", err)
			m.niceSleep(time.Second * 5)
			continue
		}

		// Wait until propagation delay period after block we plan to mine on
		onDone, injectNulls, err := m.waitFunc(ctx, prebase.TipSet.MinTimestamp())
		if err != nil {
			log.Error(err)
			continue
		}

		base, err := m.GetBestMiningCandidate(ctx)
		if err != nil {
			log.Errorf("failed to get best mining candidate: %s", err)
			continue
		}
		if base.TipSet.Equals(lastBase.TipSet) && lastBase.NullRounds == base.NullRounds {
			log.Warnf("BestMiningCandidate from the previous round: %s (nulls:%d)", lastBase.TipSet.Cids(), lastBase.NullRounds)
			m.niceSleep(time.Duration(build.BlockDelaySecs) * time.Second)
			continue
		}

		base.NullRounds += injectNulls // testing

		b, err := m.mineOne(ctx, base)
		if err != nil {
			log.Errorf("mining block failed: %+v", err)
			m.niceSleep(time.Second)
			onDone(false, err)
			continue
		}
		lastBase = *base

		onDone(b != nil, nil)

		if b != nil {
			btime := time.Unix(int64(b.Header.Timestamp), 0)
			now := build.Clock.Now()
			switch {
			case btime == now:
				// block timestamp is perfectly aligned with time.
			case btime.After(now):
				if !m.niceSleep(build.Clock.Until(btime)) {
					log.Warnf("received interrupt while waiting to broadcast block, will shutdown after block is sent out")
					build.Clock.Sleep(build.Clock.Until(btime))
				}
			default:
				log.Warnw("mined block in the past",
					"block-time", btime, "time", build.Clock.Now(), "difference", build.Clock.Since(btime))
			}

			// TODO: should do better 'anti slash' protection here
			blkKey := fmt.Sprintf("%d", b.Header.Height)
			if _, ok := m.minedBlockHeights.Get(blkKey); ok {
				log.Warnw("Created a block at the same height as another block we've created", "height", b.Header.Height, "miner", b.Header.Miner, "parents", b.Header.Parents)
				continue
			}

			m.minedBlockHeights.Add(blkKey, true)
			if err := m.api.SyncSubmitBlock(ctx, b); err != nil {
				log.Errorf("failed to submit newly mined block: %s", err)
			}
		} else {
			base.NullRounds++

			// Wait until the next epoch, plus the propagation delay, so a new tipset
			// has enough time to form.
			//
			// See:  https://github.com/filecoin-project/lotus/issues/1845
			nextRound := time.Unix(int64(base.TipSet.MinTimestamp()+build.BlockDelaySecs*uint64(base.NullRounds))+int64(build.PropagationDelaySecs), 0)

			select {
			case <-build.Clock.After(build.Clock.Until(nextRound)):
			case <-m.stop:
				stopping := m.stopping
				m.stop = nil
				m.stopping = nil
				close(stopping)
				return
			}
		}
	}
}

type MiningBase struct {
	TipSet     *types.TipSet
	NullRounds abi.ChainEpoch
}

func (m *Miner) GetBestMiningCandidate(ctx context.Context) (*MiningBase, error) {
	m.lk.Lock()
	defer m.lk.Unlock()

	bts, err := m.api.ChainHead(ctx)
	if err != nil {
		return nil, err
	}

	if m.lastWork != nil {
		if m.lastWork.TipSet.Equals(bts) {
			return m.lastWork, nil
		}

		btsw, err := m.api.ChainTipSetWeight(ctx, bts.Key())
		if err != nil {
			return nil, err
		}
		ltsw, err := m.api.ChainTipSetWeight(ctx, m.lastWork.TipSet.Key())
		if err != nil {
			return nil, err
		}

		if types.BigCmp(btsw, ltsw) <= 0 {
			return m.lastWork, nil
		}
	}

	m.lastWork = &MiningBase{TipSet: bts}
	return m.lastWork, nil
}

// mineOne attempts to mine a single block, and does so synchronously, if and
// only if we are eligible to mine.
//
// {hint/landmark}: This method coordinates all the steps involved in mining a
// block, including the condition of whether mine or not at all depending on
// whether we win the round or not.
//
// This method does the following:
//
//  1.
func (m *Miner) mineOne(ctx context.Context, base *MiningBase) (*types.BlockMsg, error) {
	log.Debugw("attempting to mine a block", "tipset", types.LogCids(base.TipSet.Cids()))
	start := build.Clock.Now()

	round := base.TipSet.Height() + base.NullRounds + 1

	mbi, err := m.api.MinerGetBaseInfo(ctx, m.address, round, base.TipSet.Key())
	if err != nil {
		return nil, xerrors.Errorf("failed to get mining base info: %w", err)
	}
	if mbi == nil {
		return nil, nil
	}
	if !mbi.HasMinPower {
		// slashed or just have no power yet
		return nil, nil
	}

	tMBI := build.Clock.Now()

	beaconPrev := mbi.PrevBeaconEntry

	tDrand := build.Clock.Now()
	bvals := mbi.BeaconEntries

	tPowercheck := build.Clock.Now()

	log.Infof("Time delta between now and our mining base: %ds (nulls: %d)", uint64(build.Clock.Now().Unix())-base.TipSet.MinTimestamp(), base.NullRounds)

	rbase := beaconPrev
	if len(bvals) > 0 {
		rbase = bvals[len(bvals)-1]
	}

	ticket, err := m.computeTicket(ctx, &rbase, base, len(bvals) > 0)
	if err != nil {
		return nil, xerrors.Errorf("scratching ticket failed: %w", err)
	}

	winner, err := gen.IsRoundWinner(ctx, base.TipSet, round, m.address, rbase, mbi, m.api)
	if err != nil {
		return nil, xerrors.Errorf("failed to check if we win next round: %w", err)
	}

	if winner == nil {
		return nil, nil
	}

	tTicket := build.Clock.Now()

	buf := new(bytes.Buffer)
	if err := m.address.MarshalCBOR(buf); err != nil {
		return nil, xerrors.Errorf("failed to marshal miner address: %w", err)
	}

	rand, err := store.DrawRandomness(rbase.Data, crypto.DomainSeparationTag_WinningPoStChallengeSeed, base.TipSet.Height()+base.NullRounds+1, buf.Bytes())
	if err != nil {
		return nil, xerrors.Errorf("failed to get randomness for winning post: %w", err)
	}

	prand := abi.PoStRandomness(rand)

	tSeed := build.Clock.Now()

	postProof, err := m.epp.ComputeProof(ctx, mbi.Sectors, prand)
	if err != nil {
		return nil, xerrors.Errorf("failed to compute winning post proof: %w", err)
	}

	// get pending messages early,
	pending, err := m.api.MpoolPending(context.TODO(), base.TipSet.Key())
	if err != nil {
		return nil, xerrors.Errorf("failed to get pending messages: %w", err)
	}

	tPending := build.Clock.Now()

	// TODO: winning post proof
	b, err := m.createBlock(base, m.address, ticket, winner, bvals, postProof, pending)
	if err != nil {
		return nil, xerrors.Errorf("failed to create block: %w", err)
	}

	tCreateBlock := build.Clock.Now()
	dur := tCreateBlock.Sub(start)
	log.Infow("mined new block", "cid", b.Cid(), "height", b.Header.Height, "took", dur)
	if dur > time.Second*time.Duration(build.BlockDelaySecs) {
		log.Warnw("CAUTION: block production took longer than the block delay. Your computer may not be fast enough to keep up",
			"tMinerBaseInfo ", tMBI.Sub(start),
			"tDrand ", tDrand.Sub(tMBI),
			"tPowercheck ", tPowercheck.Sub(tDrand),
			"tTicket ", tTicket.Sub(tPowercheck),
			"tSeed ", tSeed.Sub(tTicket),
			"tPending ", tPending.Sub(tSeed),
			"tCreateBlock ", tCreateBlock.Sub(tPending))
	}

	return b, nil
}

func (m *Miner) computeTicket(ctx context.Context, brand *types.BeaconEntry, base *MiningBase, haveNewEntries bool) (*types.Ticket, error) {
	mi, err := m.api.StateMinerInfo(ctx, m.address, types.EmptyTSK)
	if err != nil {
		return nil, err
	}
	worker, err := m.api.StateAccountKey(ctx, mi.Worker, types.EmptyTSK)
	if err != nil {
		return nil, err
	}

	buf := new(bytes.Buffer)
	if err := m.address.MarshalCBOR(buf); err != nil {
		return nil, xerrors.Errorf("failed to marshal address to cbor: %w", err)
	}

	if !haveNewEntries {
		buf.Write(base.TipSet.MinTicket().VRFProof)
	}

	input, err := store.DrawRandomness(brand.Data, crypto.DomainSeparationTag_TicketProduction, base.TipSet.Height()+base.NullRounds+1-build.TicketRandomnessLookback, buf.Bytes())
	if err != nil {
		return nil, err
	}

	vrfOut, err := gen.ComputeVRF(ctx, m.api.WalletSign, worker, input)
	if err != nil {
		return nil, err
	}

	return &types.Ticket{
		VRFProof: vrfOut,
	}, nil
}

func (m *Miner) createBlock(base *MiningBase, addr address.Address, ticket *types.Ticket,
	eproof *types.ElectionProof, bvals []types.BeaconEntry, wpostProof []abi.PoStProof, pending []*types.SignedMessage) (*types.BlockMsg, error) {
	msgs, err := SelectMessages(context.TODO(), m.api.StateGetActor, base.TipSet, pending)
	if err != nil {
		return nil, xerrors.Errorf("message filtering failed: %w", err)
	}

	if len(msgs) > build.BlockMessageLimit {
		log.Error("SelectMessages returned too many messages: ", len(msgs))
		msgs = msgs[:build.BlockMessageLimit]
	}

	uts := base.TipSet.MinTimestamp() + build.BlockDelaySecs*(uint64(base.NullRounds)+1)

	nheight := base.TipSet.Height() + base.NullRounds + 1

	// why even return this? that api call could just submit it for us
	return m.api.MinerCreateBlock(context.TODO(), &api.BlockTemplate{
		Miner:            addr,
		Parents:          base.TipSet.Key(),
		Ticket:           ticket,
		Eproof:           eproof,
		BeaconValues:     bvals,
		Messages:         msgs,
		Epoch:            nheight,
		Timestamp:        uts,
		WinningPoStProof: wpostProof,
	})
}

type actCacheEntry struct {
	act *types.Actor
	err error
}

type cachedActorLookup struct {
	tsk      types.TipSetKey
	cache    map[address.Address]actCacheEntry
	fallback ActorLookup
}

func (c *cachedActorLookup) StateGetActor(ctx context.Context, a address.Address, tsk types.TipSetKey) (*types.Actor, error) {
	if c.tsk == tsk {
		e, has := c.cache[a]
		if has {
			return e.act, e.err
		}
	}

	e, err := c.fallback(ctx, a, tsk)
	if c.tsk == tsk {
		c.cache[a] = actCacheEntry{
			act: e, err: err,
		}
	}
	return e, err
}

type ActorLookup func(context.Context, address.Address, types.TipSetKey) (*types.Actor, error)

func countFrom(msgs []*types.SignedMessage, from address.Address) (out int) {
	for _, msg := range msgs {
		if msg.Message.From == from {
			out++
		}
	}
	return out
}