// (c) 2019-2020, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.

package evm

import (
	"crypto/rand"
	"encoding/json"
	"errors"
	"fmt"
	"math/big"
	"sync"
	"sync/atomic"
	"time"

	"github.com/ava-labs/coreth"
	"github.com/ava-labs/coreth/core"
	"github.com/ava-labs/coreth/eth"
	"github.com/ava-labs/coreth/node"

	"github.com/ava-labs/go-ethereum/common"
	"github.com/ava-labs/go-ethereum/core/types"
	"github.com/ava-labs/go-ethereum/rlp"
	"github.com/ava-labs/go-ethereum/rpc"

	"github.com/ava-labs/gecko/cache"
	"github.com/ava-labs/gecko/database"
	"github.com/ava-labs/gecko/ids"
	"github.com/ava-labs/gecko/snow"
	"github.com/ava-labs/gecko/snow/choices"
	"github.com/ava-labs/gecko/snow/consensus/snowman"
	"github.com/ava-labs/gecko/utils/timer"

	commonEng "github.com/ava-labs/gecko/snow/engine/common"
)

const (
	lastAcceptedKey = "snowman_lastAccepted"
)

const (
	minBlockTime = 250 * time.Millisecond
	maxBlockTime = 1000 * time.Millisecond
	batchSize    = 250
)

const (
	bdTimerStateMin = iota
	bdTimerStateMax
	bdTimerStateLong
)

var (
	errEmptyBlock     = errors.New("empty block")
	errCreateBlock    = errors.New("couldn't create block")
	errUnknownBlock   = errors.New("unknown block")
	errBlockFrequency = errors.New("too frequent block issuance")
	errUnsupportedFXs = errors.New("unsupported feature extensions")
)

func maxDuration(x, y time.Duration) time.Duration {
	if x > y {
		return x
	}
	return y
}

// VM implements the snowman.ChainVM interface
type VM struct {
	ctx *snow.Context

	chainID           *big.Int
	networkID         uint64
	chain             *coreth.ETHChain
	chaindb           Database
	newBlockChan      chan *Block
	networkChan       chan<- commonEng.Message
	newTxPoolHeadChan chan core.NewTxPoolHeadEvent

	txPoolStabilizedHead common.Hash
	txPoolStabilizedOk   chan struct{}
	txPoolStabilizedLock sync.Mutex

	metalock                     sync.Mutex
	blockCache, blockStatusCache cache.LRU
	lastAccepted                 *Block
	writingMetadata              uint32

	bdlock          sync.Mutex
	blockDelayTimer *timer.Timer
	bdTimerState    int8
	bdGenWaitFlag   bool
	bdGenFlag       bool

	genlock      sync.Mutex
	txSubmitChan <-chan struct{}
}

/*
 ******************************************************************************
 ********************************* Snowman API ********************************
 ******************************************************************************
 */

// Initialize implements the snowman.ChainVM interface
func (vm *VM) Initialize(
	ctx *snow.Context,
	db database.Database,
	b []byte,
	toEngine chan<- commonEng.Message,
	fxs []*commonEng.Fx,
) error {
	if len(fxs) > 0 {
		return errUnsupportedFXs
	}

	vm.ctx = ctx
	vm.chaindb = Database{db}
	g := new(core.Genesis)
	err := json.Unmarshal(b, g)
	if err != nil {
		return err
	}

	vm.chainID = g.Config.ChainID

	config := eth.DefaultConfig
	config.ManualCanonical = true
	config.Genesis = g
	config.Miner.ManualMining = true
	config.Miner.DisableUncle = true
	if err := config.SetGCMode("archive"); err != nil {
		panic(err)
	}
	nodecfg := node.Config{NoUSB: true}
	chain := coreth.NewETHChain(&config, &nodecfg, nil, vm.chaindb)
	vm.chain = chain
	vm.networkID = config.NetworkId
	chain.SetOnHeaderNew(func(header *types.Header) {
		hid := make([]byte, 32)
		_, err := rand.Read(hid)
		if err != nil {
			panic("cannot generate hid")
		}
		header.Extra = append(header.Extra, hid...)
	})
	chain.SetOnSeal(func(block *types.Block) error {
		if len(block.Transactions()) == 0 {
			// this could happen due to the async logic of geth tx pool
			vm.newBlockChan <- nil
			return errEmptyBlock
		}
		return nil
	})
	chain.SetOnSealFinish(func(block *types.Block) error {
		vm.ctx.Log.Verbo("EVM sealed a block")

		blk := &Block{
			id:       ids.NewID(block.Hash()),
			ethBlock: block,
			vm:       vm,
		}
		vm.newBlockChan <- blk
		vm.updateStatus(ids.NewID(block.Hash()), choices.Processing)
		vm.txPoolStabilizedLock.Lock()
		vm.txPoolStabilizedHead = block.Hash()
		vm.txPoolStabilizedLock.Unlock()
		return nil
	})
	chain.SetOnQueryAcceptedBlock(func() *types.Block {
		return vm.getLastAccepted().ethBlock
	})
	vm.blockCache = cache.LRU{Size: 2048}
	vm.blockStatusCache = cache.LRU{Size: 1024}
	vm.newBlockChan = make(chan *Block)
	vm.networkChan = toEngine
	vm.blockDelayTimer = timer.NewTimer(func() {
		vm.bdlock.Lock()
		switch vm.bdTimerState {
		case bdTimerStateMin:
			vm.bdTimerState = bdTimerStateMax
			vm.blockDelayTimer.SetTimeoutIn(maxDuration(maxBlockTime-minBlockTime, 0))
		case bdTimerStateMax:
			vm.bdTimerState = bdTimerStateLong
		}
		tryAgain := vm.bdGenWaitFlag
		vm.bdlock.Unlock()
		if tryAgain {
			vm.tryBlockGen()
		}
	})
	go ctx.Log.RecoverAndPanic(vm.blockDelayTimer.Dispatch)

	vm.bdTimerState = bdTimerStateLong
	vm.bdGenWaitFlag = true
	vm.newTxPoolHeadChan = make(chan core.NewTxPoolHeadEvent, 1)
	vm.txPoolStabilizedOk = make(chan struct{}, 1)
	chain.GetTxPool().SubscribeNewHeadEvent(vm.newTxPoolHeadChan)
	// TODO: shutdown this go routine
	go ctx.Log.RecoverAndPanic(func() {
		for {
			select {
			case h := <-vm.newTxPoolHeadChan:
				vm.txPoolStabilizedLock.Lock()
				if vm.txPoolStabilizedHead == h.Block.Hash() {
					vm.txPoolStabilizedOk <- struct{}{}
					vm.txPoolStabilizedHead = common.Hash{}
				}
				vm.txPoolStabilizedLock.Unlock()
			}
		}
	})
	chain.Start()

	var lastAccepted *types.Block
	if b, err := vm.chaindb.Get([]byte(lastAcceptedKey)); err == nil {
		var hash common.Hash
		if err = rlp.DecodeBytes(b, &hash); err == nil {
			if block := chain.GetBlockByHash(hash); block == nil {
				vm.ctx.Log.Debug("lastAccepted block not found in chaindb")
			} else {
				lastAccepted = block
			}
		}
	}
	if lastAccepted == nil {
		vm.ctx.Log.Debug("lastAccepted is unavailable, setting to the genesis block")
		lastAccepted = chain.GetGenesisBlock()
	}
	vm.lastAccepted = &Block{
		id:       ids.NewID(lastAccepted.Hash()),
		ethBlock: lastAccepted,
		vm:       vm,
	}
	vm.ctx.Log.Info(fmt.Sprintf("lastAccepted = %s", vm.lastAccepted.ethBlock.Hash().Hex()))

	// TODO: shutdown this go routine
	go vm.ctx.Log.RecoverAndPanic(func() {
		vm.txSubmitChan = vm.chain.GetTxSubmitCh()
		for {
			select {
			case <-vm.txSubmitChan:
				vm.ctx.Log.Verbo("New tx detected, trying to generate a block")
				vm.tryBlockGen()
			case <-time.After(5 * time.Second):
				vm.tryBlockGen()
			}
		}
	})

	return nil
}

// Shutdown implements the snowman.ChainVM interface
func (vm *VM) Shutdown() {
	if vm.ctx == nil {
		return
	}

	vm.writeBackMetadata()
	vm.chain.Stop()
}

// BuildBlock implements the snowman.ChainVM interface
func (vm *VM) BuildBlock() (snowman.Block, error) {
	vm.chain.GenBlock()
	block := <-vm.newBlockChan
	if block == nil {
		return nil, errCreateBlock
	}
	// reset the min block time timer
	vm.bdlock.Lock()
	vm.bdTimerState = bdTimerStateMin
	vm.bdGenWaitFlag = false
	vm.bdGenFlag = false
	vm.blockDelayTimer.SetTimeoutIn(minBlockTime)
	vm.bdlock.Unlock()

	vm.ctx.Log.Debug("built block 0x%x", block.ID().Bytes())
	// make sure Tx Pool is updated
	<-vm.txPoolStabilizedOk
	return block, nil
}

// ParseBlock implements the snowman.ChainVM interface
func (vm *VM) ParseBlock(b []byte) (snowman.Block, error) {
	vm.metalock.Lock()
	defer vm.metalock.Unlock()

	ethBlock := new(types.Block)
	if err := rlp.DecodeBytes(b, ethBlock); err != nil {
		return nil, err
	}
	block := &Block{
		id:       ids.NewID(ethBlock.Hash()),
		ethBlock: ethBlock,
		vm:       vm,
	}
	vm.blockCache.Put(block.ID(), block)
	return block, nil
}

// GetBlock implements the snowman.ChainVM interface
func (vm *VM) GetBlock(id ids.ID) (snowman.Block, error) {
	vm.metalock.Lock()
	defer vm.metalock.Unlock()

	block := vm.getBlock(id)
	if block == nil {
		return nil, errUnknownBlock
	}
	return block, nil
}

// SetPreference sets what the current tail of the chain is
func (vm *VM) SetPreference(blkID ids.ID) {
	err := vm.chain.SetTail(blkID.Key())
	vm.ctx.Log.AssertNoError(err)
}

// LastAccepted returns the ID of the block that was last accepted
func (vm *VM) LastAccepted() ids.ID {
	vm.metalock.Lock()
	defer vm.metalock.Unlock()

	return vm.lastAccepted.ID()
}

// CreateHandlers makes new http handlers that can handle API calls
func (vm *VM) CreateHandlers() map[string]*commonEng.HTTPHandler {
	handler := vm.chain.NewRPCHandler()
	vm.chain.AttachEthService(handler, []string{"eth", "personal", "txpool"})
	handler.RegisterName("net", &NetAPI{vm})
	handler.RegisterName("snowman", &SnowmanAPI{vm})
	handler.RegisterName("web3", &Web3API{})
	handler.RegisterName("debug", &DebugAPI{vm})

	return map[string]*commonEng.HTTPHandler{
		"/rpc": &commonEng.HTTPHandler{LockOptions: commonEng.NoLock, Handler: handler},
		"/ws":  &commonEng.HTTPHandler{LockOptions: commonEng.NoLock, Handler: handler.WebsocketHandler([]string{"*"})},
	}
}

// CreateStaticHandlers makes new http handlers that can handle API calls
func (vm *VM) CreateStaticHandlers() map[string]*commonEng.HTTPHandler {
	handler := rpc.NewServer()
	handler.RegisterName("static", &StaticService{})
	return map[string]*commonEng.HTTPHandler{
		"/rpc": &commonEng.HTTPHandler{LockOptions: commonEng.NoLock, Handler: handler},
		"/ws":  &commonEng.HTTPHandler{LockOptions: commonEng.NoLock, Handler: handler.WebsocketHandler([]string{"*"})},
	}
}

/*
 ******************************************************************************
 *********************************** Helpers **********************************
 ******************************************************************************
 */

func (vm *VM) updateStatus(blockID ids.ID, status choices.Status) {
	vm.metalock.Lock()
	defer vm.metalock.Unlock()

	if status == choices.Accepted {
		vm.lastAccepted = vm.getBlock(blockID)
		// TODO: improve this naive implementation
		if atomic.SwapUint32(&vm.writingMetadata, 1) == 0 {
			go vm.ctx.Log.RecoverAndPanic(vm.writeBackMetadata)
		}
	}
	vm.blockStatusCache.Put(blockID, status)
}

func (vm *VM) getCachedBlock(blockID ids.ID) *types.Block {
	return vm.chain.GetBlockByHash(blockID.Key())
}

func (vm *VM) tryBlockGen() error {
	vm.bdlock.Lock()
	defer vm.bdlock.Unlock()
	if vm.bdGenFlag {
		// skip if one call already generates a block in this round
		return nil
	}
	vm.bdGenWaitFlag = true

	vm.genlock.Lock()
	defer vm.genlock.Unlock()
	// get pending size
	size, err := vm.chain.PendingSize()
	if err != nil {
		return err
	}
	if size == 0 {
		return nil
	}

	switch vm.bdTimerState {
	case bdTimerStateMin:
		return nil
	case bdTimerStateMax:
		if size < batchSize {
			return nil
		}
	case bdTimerStateLong:
		// timeout; go ahead and generate a new block anyway
	}
	select {
	case vm.networkChan <- commonEng.PendingTxs:
		// successfully push out the notification; this round ends
		vm.bdGenFlag = true
	default:
		return errBlockFrequency
	}
	return nil
}

func (vm *VM) getCachedStatus(blockID ids.ID) choices.Status {
	vm.metalock.Lock()
	defer vm.metalock.Unlock()
	status := choices.Processing

	if statusIntf, ok := vm.blockStatusCache.Get(blockID); ok {
		status = statusIntf.(choices.Status)
	} else {
		blk := vm.chain.GetBlockByHash(blockID.Key())
		if blk == nil {
			return choices.Unknown
		}
		acceptedBlk := vm.lastAccepted.ethBlock

		// TODO: There must be a better way of doing this.
		// Traverse up the chain from the lower block until the indices match
		highBlock := blk
		lowBlock := acceptedBlk
		if highBlock.Number().Cmp(lowBlock.Number()) < 0 {
			highBlock, lowBlock = lowBlock, highBlock
		}
		for highBlock.Number().Cmp(lowBlock.Number()) > 0 {
			highBlock = vm.chain.GetBlockByHash(highBlock.ParentHash())
		}

		if highBlock.Hash() == lowBlock.Hash() { // on the same branch
			if blk.Number().Cmp(acceptedBlk.Number()) <= 0 {
				status = choices.Accepted
			}
		} else { // on different branches
			status = choices.Rejected
		}
	}

	vm.blockStatusCache.Put(blockID, status)
	return status
}

func (vm *VM) getBlock(id ids.ID) *Block {
	if blockIntf, ok := vm.blockCache.Get(id); ok {
		return blockIntf.(*Block)
	}
	ethBlock := vm.getCachedBlock(id)
	if ethBlock == nil {
		return nil
	}
	block := &Block{
		id:       ids.NewID(ethBlock.Hash()),
		ethBlock: ethBlock,
		vm:       vm,
	}
	vm.blockCache.Put(id, block)
	return block
}

func (vm *VM) issueRemoteTxs(txs []*types.Transaction) error {
	errs := vm.chain.AddRemoteTxs(txs)
	for _, err := range errs {
		if err != nil {
			return err
		}
	}
	return vm.tryBlockGen()
}

func (vm *VM) writeBackMetadata() {
	vm.metalock.Lock()
	defer vm.metalock.Unlock()

	b, err := rlp.EncodeToBytes(vm.lastAccepted.ethBlock.Hash())
	if err != nil {
		vm.ctx.Log.Error("snowman-eth: error while writing back metadata")
		return
	}
	vm.ctx.Log.Debug("writing back metadata")
	vm.chaindb.Put([]byte(lastAcceptedKey), b)
	atomic.StoreUint32(&vm.writingMetadata, 0)
}

func (vm *VM) getLastAccepted() *Block {
	vm.metalock.Lock()
	defer vm.metalock.Unlock()

	return vm.lastAccepted
}