package miner

import (
	"context"
	"errors"
	"fmt"
	"math/big"
	"net"
	"net/http"
	"sync"
	"sync/atomic"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/bidutil"
	"github.com/ethereum/go-ethereum/consensus"
	"github.com/ethereum/go-ethereum/core"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/event"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/miner/builderclient"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/rpc"
)

const (
	// maxBidPerBuilderPerBlock is the max bid number per builder
	maxBidPerBuilderPerBlock = 3

	commitInterruptBetterBid = 1

	// leftOverTimeRate is the rate of left over time to simulate a bid
	leftOverTimeRate = 11
	// leftOverTimeScale is the scale of left over time to simulate a bid
	leftOverTimeScale = 10
)

var (
	diffInTurn = big.NewInt(2) // the difficulty of a block that proposed by an in-turn validator
)

var (
	dialer = &net.Dialer{
		Timeout:   time.Second,
		KeepAlive: 60 * time.Second,
	}

	transport = &http.Transport{
		DialContext:         dialer.DialContext,
		MaxIdleConnsPerHost: 50,
		MaxConnsPerHost:     50,
		IdleConnTimeout:     90 * time.Second,
	}

	client = &http.Client{
		Timeout:   5 * time.Second,
		Transport: transport,
	}
)

type WorkPreparer interface {
	prepareWork(params *generateParams) (*environment, error)
	etherbase() common.Address
}

// simBidReq is the request for simulating a bid
type simBidReq struct {
	bid         *BidRuntime
	interruptCh chan int32
}

// bidSimulator is in charge of receiving bid from builders, reporting issue to builders.
// And take care of bid simulation, rewards computing, best bid maintaining.
type bidSimulator struct {
	config        *MevConfig
	delayLeftOver time.Duration
	chain         *core.BlockChain
	chainConfig   *params.ChainConfig
	workPreparer  WorkPreparer

	running atomic.Bool // controlled by miner
	exitCh  chan struct{}

	bidReceiving atomic.Bool // controlled by config and eth.AdminAPI

	chainHeadCh  chan core.ChainHeadEvent
	chainHeadSub event.Subscription

	sentryCli *builderclient.Client

	// builder info (warning: only keep status in memory!)
	buildersMu sync.RWMutex
	builders   map[common.Address]*builderclient.Client

	// channels
	simBidCh chan *simBidReq
	newBidCh chan *types.Bid

	pendingMu sync.RWMutex
	pending   map[uint64]map[common.Address]map[common.Hash]struct{} // blockNumber -> builder -> bidHash -> struct{}

	bestBidMu sync.RWMutex
	bestBid   map[common.Hash]*BidRuntime // prevBlockHash -> bidRuntime

	simBidMu      sync.RWMutex
	simulatingBid map[common.Hash]*BidRuntime // prevBlockHash -> bidRuntime, in the process of simulation
}

func newBidSimulator(
	config *MevConfig,
	delayLeftOver time.Duration,
	chainConfig *params.ChainConfig,
	chain *core.BlockChain,
	workPreparer WorkPreparer,
) *bidSimulator {
	b := &bidSimulator{
		config:        config,
		delayLeftOver: delayLeftOver,
		chainConfig:   chainConfig,
		chain:         chain,
		workPreparer:  workPreparer,
		exitCh:        make(chan struct{}),
		chainHeadCh:   make(chan core.ChainHeadEvent, chainHeadChanSize),
		builders:      make(map[common.Address]*builderclient.Client),
		simBidCh:      make(chan *simBidReq),
		newBidCh:      make(chan *types.Bid, 100),
		pending:       make(map[uint64]map[common.Address]map[common.Hash]struct{}),
		bestBid:       make(map[common.Hash]*BidRuntime),
		simulatingBid: make(map[common.Hash]*BidRuntime),
	}

	b.chainHeadSub = chain.SubscribeChainHeadEvent(b.chainHeadCh)

	if config.Enabled {
		b.bidReceiving.Store(true)
		b.dialSentryAndBuilders()

		if len(b.builders) == 0 {
			log.Warn("BidSimulator: no valid builders")
		}
	}

	go b.clearLoop()
	go b.mainLoop()
	go b.newBidLoop()

	return b
}

func (b *bidSimulator) dialSentryAndBuilders() {
	var sentryCli *builderclient.Client
	var err error

	if b.config.SentryURL != "" {
		sentryCli, err = builderclient.DialOptions(context.Background(), b.config.SentryURL, rpc.WithHTTPClient(client))
		if err != nil {
			log.Error("BidSimulator: failed to dial sentry", "url", b.config.SentryURL, "err", err)
		}
	}

	b.sentryCli = sentryCli

	for _, v := range b.config.Builders {
		_ = b.AddBuilder(v.Address, v.URL)
	}
}

func (b *bidSimulator) start() {
	b.running.Store(true)
}

func (b *bidSimulator) stop() {
	b.running.Store(false)
}

func (b *bidSimulator) close() {
	b.running.Store(false)
	close(b.exitCh)
}

func (b *bidSimulator) isRunning() bool {
	return b.running.Load()
}

func (b *bidSimulator) receivingBid() bool {
	return b.bidReceiving.Load()
}

func (b *bidSimulator) startReceivingBid() {
	b.dialSentryAndBuilders()
	b.bidReceiving.Store(true)
}

func (b *bidSimulator) stopReceivingBid() {
	b.bidReceiving.Store(false)
}

func (b *bidSimulator) AddBuilder(builder common.Address, url string) error {
	b.buildersMu.Lock()
	defer b.buildersMu.Unlock()

	if b.sentryCli != nil {
		b.builders[builder] = b.sentryCli
	} else {
		var builderCli *builderclient.Client

		if url != "" {
			var err error

			builderCli, err = builderclient.DialOptions(context.Background(), url, rpc.WithHTTPClient(client))
			if err != nil {
				log.Error("BidSimulator: failed to dial builder", "url", url, "err", err)
				return err
			}
		}

		b.builders[builder] = builderCli
	}

	return nil
}

func (b *bidSimulator) RemoveBuilder(builder common.Address) error {
	b.buildersMu.Lock()
	defer b.buildersMu.Unlock()

	delete(b.builders, builder)

	return nil
}

func (b *bidSimulator) ExistBuilder(builder common.Address) bool {
	b.buildersMu.RLock()
	defer b.buildersMu.RUnlock()

	_, ok := b.builders[builder]

	return ok
}

func (b *bidSimulator) SetBestBid(prevBlockHash common.Hash, bid *BidRuntime) {
	b.bestBidMu.Lock()
	defer b.bestBidMu.Unlock()

	b.bestBid[prevBlockHash] = bid
}

func (b *bidSimulator) GetBestBid(prevBlockHash common.Hash) *BidRuntime {
	b.bestBidMu.RLock()
	defer b.bestBidMu.RUnlock()

	return b.bestBid[prevBlockHash]
}

func (b *bidSimulator) SetSimulatingBid(prevBlockHash common.Hash, bid *BidRuntime) {
	b.simBidMu.Lock()
	defer b.simBidMu.Unlock()

	b.simulatingBid[prevBlockHash] = bid
}

func (b *bidSimulator) GetSimulatingBid(prevBlockHash common.Hash) *BidRuntime {
	b.simBidMu.RLock()
	defer b.simBidMu.RUnlock()

	return b.simulatingBid[prevBlockHash]
}

func (b *bidSimulator) RemoveSimulatingBid(prevBlockHash common.Hash) {
	b.simBidMu.Lock()
	defer b.simBidMu.Unlock()

	delete(b.simulatingBid, prevBlockHash)
}

func (b *bidSimulator) mainLoop() {
	defer b.chainHeadSub.Unsubscribe()

	for {
		select {
		case req := <-b.simBidCh:
			if !b.isRunning() {
				continue
			}

			b.simBid(req.interruptCh, req.bid)

		// System stopped
		case <-b.exitCh:
			return

		case <-b.chainHeadSub.Err():
			return
		}
	}
}

func (b *bidSimulator) newBidLoop() {
	var (
		interruptCh chan int32
	)

	// commit aborts in-flight bid execution with given signal and resubmits a new one.
	commit := func(reason int32, bidRuntime *BidRuntime) {
		// if the left time is not enough to do simulation, return
		var simDuration time.Duration
		if lastBid := b.GetBestBid(bidRuntime.bid.ParentHash); lastBid != nil && lastBid.duration != 0 {
			simDuration = lastBid.duration
		}

		if time.Until(b.bidMustBefore(bidRuntime.bid.ParentHash)) <= simDuration*leftOverTimeRate/leftOverTimeScale {
			return
		}

		if interruptCh != nil {
			// each commit work will have its own interruptCh to stop work with a reason
			interruptCh <- reason
			close(interruptCh)
		}
		interruptCh = make(chan int32, 1)
		select {
		case b.simBidCh <- &simBidReq{interruptCh: interruptCh, bid: bidRuntime}:
		case <-b.exitCh:
			return
		}
	}

	for {
		select {
		case newBid := <-b.newBidCh:
			if !b.isRunning() {
				continue
			}

			// check the block reward and validator reward of the newBid
			expectedBlockReward := newBid.GasFee
			expectedValidatorReward := new(big.Int).Mul(expectedBlockReward, big.NewInt(int64(b.config.ValidatorCommission)))
			expectedValidatorReward.Div(expectedValidatorReward, big.NewInt(10000))
			expectedValidatorReward.Sub(expectedValidatorReward, newBid.BuilderFee)

			if expectedValidatorReward.Cmp(big.NewInt(0)) < 0 {
				// damage self profit, ignore
				continue
			}

			bidRuntime := &BidRuntime{
				bid:                     newBid,
				expectedBlockReward:     expectedBlockReward,
				expectedValidatorReward: expectedValidatorReward,
				packedBlockReward:       big.NewInt(0),
				packedValidatorReward:   big.NewInt(0),
			}

			// TODO(renee-) opt bid comparation

			simulatingBid := b.GetSimulatingBid(newBid.ParentHash)
			// simulatingBid is nil means there is no bid in simulation
			if simulatingBid == nil {
				// bestBid is nil means bid is the first bid
				bestBid := b.GetBestBid(newBid.ParentHash)
				if bestBid == nil {
					commit(commitInterruptBetterBid, bidRuntime)
					continue
				}

				// if bestBid is not nil, check if newBid is better than bestBid
				if bidRuntime.expectedBlockReward.Cmp(bestBid.expectedBlockReward) > 0 &&
					bidRuntime.expectedValidatorReward.Cmp(bestBid.expectedValidatorReward) > 0 {
					// if both reward are better than last simulating newBid, commit for simulation
					commit(commitInterruptBetterBid, bidRuntime)
					continue
				}

				continue
			}

			// simulatingBid must be better than bestBid, if newBid is better than simulatingBid, commit for simulation
			if bidRuntime.expectedBlockReward.Cmp(simulatingBid.expectedBlockReward) > 0 &&
				bidRuntime.expectedValidatorReward.Cmp(simulatingBid.expectedValidatorReward) > 0 {
				// if both reward are better than last simulating newBid, commit for simulation
				commit(commitInterruptBetterBid, bidRuntime)
				continue
			}

		case <-b.exitCh:
			return
		}
	}
}

func (b *bidSimulator) bidMustBefore(parentHash common.Hash) time.Time {
	parentHeader := b.chain.GetHeaderByHash(parentHash)
	return bidutil.BidMustBefore(parentHeader, b.chainConfig.Parlia.Period, b.delayLeftOver)
}

func (b *bidSimulator) bidBetterBefore(parentHash common.Hash) time.Time {
	parentHeader := b.chain.GetHeaderByHash(parentHash)
	return bidutil.BidBetterBefore(parentHeader, b.chainConfig.Parlia.Period, b.delayLeftOver, b.config.BidSimulationLeftOver)
}

func (b *bidSimulator) clearLoop() {
	clearFn := func(parentHash common.Hash, blockNumber uint64) {
		b.pendingMu.Lock()
		delete(b.pending, blockNumber)
		b.pendingMu.Unlock()

		b.bestBidMu.Lock()
		if bid, ok := b.bestBid[parentHash]; ok {
			bid.env.discard()
		}
		delete(b.bestBid, parentHash)
		for k, v := range b.bestBid {
			if v.bid.BlockNumber <= blockNumber-core.TriesInMemory {
				v.env.discard()
				delete(b.bestBid, k)
			}
		}
		b.bestBidMu.Unlock()

		b.simBidMu.Lock()
		if bid, ok := b.simulatingBid[parentHash]; ok {
			bid.env.discard()
		}
		delete(b.simulatingBid, parentHash)
		for k, v := range b.simulatingBid {
			if v.bid.BlockNumber <= blockNumber-core.TriesInMemory {
				v.env.discard()
				delete(b.simulatingBid, k)
			}
		}
		b.simBidMu.Unlock()
	}

	for head := range b.chainHeadCh {
		if !b.isRunning() {
			continue
		}

		clearFn(head.Block.ParentHash(), head.Block.NumberU64())
	}
}

// sendBid checks if the bid is already exists or if the builder sends too many bids,
// if yes, return error, if not, add bid into newBid chan waiting for judge profit.
func (b *bidSimulator) sendBid(_ context.Context, bid *types.Bid) error {
	timer := time.NewTimer(1 * time.Second)
	defer timer.Stop()
	select {
	case b.newBidCh <- bid:
		b.AddPending(bid.BlockNumber, bid.Builder, bid.Hash())
		return nil
	case <-timer.C:
		return types.ErrMevBusy
	}
}

func (b *bidSimulator) CheckPending(blockNumber uint64, builder common.Address, bidHash common.Hash) error {
	b.pendingMu.Lock()
	defer b.pendingMu.Unlock()

	// check if bid exists or if builder sends too many bids
	if _, ok := b.pending[blockNumber]; !ok {
		b.pending[blockNumber] = make(map[common.Address]map[common.Hash]struct{})
	}

	if _, ok := b.pending[blockNumber][builder]; !ok {
		b.pending[blockNumber][builder] = make(map[common.Hash]struct{})
	}

	if _, ok := b.pending[blockNumber][builder][bidHash]; ok {
		return errors.New("bid already exists")
	}

	if len(b.pending[blockNumber][builder]) >= maxBidPerBuilderPerBlock {
		return errors.New("too many bids")
	}

	return nil
}

func (b *bidSimulator) AddPending(blockNumber uint64, builder common.Address, bidHash common.Hash) {
	b.pendingMu.Lock()
	defer b.pendingMu.Unlock()

	b.pending[blockNumber][builder][bidHash] = struct{}{}
}

// simBid simulates a newBid with txs.
// simBid does not enable state prefetching when commit transaction.
func (b *bidSimulator) simBid(interruptCh chan int32, bidRuntime *BidRuntime) {
	// prevent from stopping happen in time interval from sendBid to simBid
	if !b.isRunning() || !b.receivingBid() {
		return
	}

	var (
		blockNumber = bidRuntime.bid.BlockNumber
		parentHash  = bidRuntime.bid.ParentHash
		builder     = bidRuntime.bid.Builder
		err         error
		success     bool
	)

	// ensure simulation exited then start next simulation
	b.SetSimulatingBid(parentHash, bidRuntime)

	defer func(simStart time.Time) {
		logCtx := []any{
			"blockNumber", blockNumber,
			"parentHash", parentHash,
			"builder", builder,
			"gasUsed", bidRuntime.bid.GasUsed,
		}

		if bidRuntime.env != nil {
			logCtx = append(logCtx, "gasLimit", bidRuntime.env.header.GasLimit)

			if err != nil || !success {
				bidRuntime.env.discard()
			}
		}

		if err != nil {
			logCtx = append(logCtx, "err", err)
			log.Debug("bid simulation failed", logCtx...)

			go b.reportIssue(bidRuntime, err)
		}

		if success {
			bidRuntime.duration = time.Since(simStart)
		}

		b.RemoveSimulatingBid(parentHash)
	}(time.Now())

	// prepareWork will configure header with a suitable time according to consensus
	// prepareWork will start trie prefetching
	if bidRuntime.env, err = b.workPreparer.prepareWork(&generateParams{
		parentHash: bidRuntime.bid.ParentHash,
		coinbase:   b.workPreparer.etherbase(),
	}); err != nil {
		return
	}

	gasLimit := bidRuntime.env.header.GasLimit
	if bidRuntime.env.gasPool == nil {
		bidRuntime.env.gasPool = new(core.GasPool).AddGas(gasLimit)
		bidRuntime.env.gasPool.SubGas(params.SystemTxsGas)
	}

	if bidRuntime.bid.GasUsed > bidRuntime.env.gasPool.Gas() {
		err = errors.New("gas used exceeds gas limit")
		return
	}

	for _, tx := range bidRuntime.bid.Txs {
		select {
		case <-interruptCh:
			err = errors.New("simulation abort due to better bid arrived")
			return

		case <-b.exitCh:
			err = errors.New("miner exit")
			return

		default:
		}

		// Start executing the transaction
		bidRuntime.env.state.SetTxContext(tx.Hash(), bidRuntime.env.tcount)

		err = bidRuntime.commitTransaction(b.chain, b.chainConfig, tx)
		if err != nil {
			log.Error("BidSimulator: failed to commit tx", "bidHash", bidRuntime.bid.Hash(), "tx", tx.Hash(), "err", err)
			err = fmt.Errorf("invalid tx in bid, %v", err)
			return
		}

		bidRuntime.env.tcount++
	}

	bidRuntime.packReward(b.config.ValidatorCommission)

	// return if bid is invalid, reportIssue issue to mev-sentry/builder if simulation is fully done
	if !bidRuntime.validReward() {
		err = errors.New("reward does not achieve the expectation")
		return
	}

	bestBid := b.GetBestBid(parentHash)

	if bestBid == nil {
		b.SetBestBid(bidRuntime.bid.ParentHash, bidRuntime)
		success = true
		return
	}

	// this is the simplest strategy: best for all the delegators.
	if bidRuntime.packedBlockReward.Cmp(bestBid.packedBlockReward) > 0 {
		b.SetBestBid(bidRuntime.bid.ParentHash, bidRuntime)
		success = true
		return
	}
}

// reportIssue reports the issue to the mev-sentry
func (b *bidSimulator) reportIssue(bidRuntime *BidRuntime, err error) {
	cli := b.builders[bidRuntime.bid.Builder]
	if cli != nil {
		cli.ReportIssue(context.Background(), &types.BidIssue{
			Validator: bidRuntime.env.header.Coinbase,
			Builder:   bidRuntime.bid.Builder,
			Message:   err.Error(),
		})
	}
}

type BidRuntime struct {
	bid *types.Bid

	env *environment

	expectedBlockReward     *big.Int
	expectedValidatorReward *big.Int

	packedBlockReward     *big.Int
	packedValidatorReward *big.Int

	duration time.Duration
}

func (r *BidRuntime) validReward() bool {
	return r.packedBlockReward.Cmp(r.expectedBlockReward) >= 0 &&
		r.packedValidatorReward.Cmp(r.expectedValidatorReward) >= 0
}

// packReward calculates packedBlockReward and packedValidatorReward
func (r *BidRuntime) packReward(validatorCommission uint64) {
	r.packedBlockReward = r.env.state.GetBalance(consensus.SystemAddress).ToBig()
	r.packedValidatorReward = new(big.Int).Mul(r.packedBlockReward, big.NewInt(int64(validatorCommission)))
	r.packedValidatorReward.Div(r.packedValidatorReward, big.NewInt(10000))
	r.packedValidatorReward.Sub(r.packedValidatorReward, r.bid.BuilderFee)
}

func (r *BidRuntime) commitTransaction(chain *core.BlockChain, chainConfig *params.ChainConfig, tx *types.Transaction) error {
	var (
		env  = r.env
		snap = env.state.Snapshot()
		gp   = env.gasPool.Gas()
		sc   *types.BlobTxSidecar
	)

	if tx.Type() == types.BlobTxType {
		sc := tx.BlobTxSidecar()
		if sc == nil {
			return errors.New("blob transaction without blobs in miner")
		}
		// Checking against blob gas limit: It's kind of ugly to perform this check here, but there
		// isn't really a better place right now. The blob gas limit is checked at block validation time
		// and not during execution. This means core.ApplyTransaction will not return an error if the
		// tx has too many blobs. So we have to explicitly check it here.
		if (env.blobs+len(sc.Blobs))*params.BlobTxBlobGasPerBlob > params.MaxBlobGasPerBlock {
			return errors.New("max data blobs reached")
		}
	}

	receipt, err := core.ApplyTransaction(chainConfig, chain, &env.coinbase, env.gasPool, env.state, env.header, tx,
		&env.header.GasUsed, *chain.GetVMConfig(), core.NewReceiptBloomGenerator())
	if err != nil {
		env.state.RevertToSnapshot(snap)
		env.gasPool.SetGas(gp)
		return err
	}

	if tx.Type() == types.BlobTxType {
		env.txs = append(env.txs, tx.WithoutBlobTxSidecar())
		env.receipts = append(env.receipts, receipt)
		env.sidecars = append(env.sidecars, sc)
		env.blobs += len(sc.Blobs)
		*env.header.BlobGasUsed += receipt.BlobGasUsed
	} else {
		env.txs = append(env.txs, tx)
		env.receipts = append(env.receipts, receipt)
	}

	return nil
}