// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package light

import (
	"fmt"
	"sync"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/event"
	"github.com/ethereum/go-ethereum/logger"
	"github.com/ethereum/go-ethereum/logger/glog"
	"github.com/ethereum/go-ethereum/rlp"
	"golang.org/x/net/context"
)

// txPermanent is the number of mined blocks after a mined transaction is
// considered permanent and no rollback is expected
var txPermanent = uint64(500)

// TxPool implements the transaction pool for light clients, which keeps track
// of the status of locally created transactions, detecting if they are included
// in a block (mined) or rolled back. There are no queued transactions since we
// always receive all locally signed transactions in the same order as they are
// created.
type TxPool struct {
	config *core.ChainConfig
	quit     chan bool
	eventMux *event.TypeMux
	events   event.Subscription
	mu       sync.RWMutex
	chain    *LightChain
	odr      OdrBackend
	chainDb  ethdb.Database
	relay    TxRelayBackend
	head     common.Hash
	nonce    map[common.Address]uint64            // "pending" nonce
	pending  map[common.Hash]*types.Transaction   // pending transactions by tx hash
	mined    map[common.Hash][]*types.Transaction // mined transactions by block hash
	clearIdx uint64                               // earliest block nr that can contain mined tx info

	homestead bool
}

// TxRelayBackend provides an interface to the mechanism that forwards transacions
// to the ETH network. The implementations of the functions should be non-blocking.
//
// Send instructs backend to forward new transactions
// NewHead notifies backend about a new head after processed by the tx pool,
//  including  mined and rolled back transactions since the last event
// Discard notifies backend about transactions that should be discarded either
//  because they have been replaced by a re-send or because they have been mined
//  long ago and no rollback is expected
type TxRelayBackend interface {
	Send(txs types.Transactions)
	NewHead(head common.Hash, mined []common.Hash, rollback []common.Hash)
	Discard(hashes []common.Hash)
}

// NewTxPool creates a new light transaction pool
func NewTxPool(config *core.ChainConfig, eventMux *event.TypeMux, chain *LightChain, relay TxRelayBackend) *TxPool {
	pool := &TxPool{
		config:		config,
		nonce:    make(map[common.Address]uint64),
		pending:  make(map[common.Hash]*types.Transaction),
		mined:    make(map[common.Hash][]*types.Transaction),
		quit:     make(chan bool),
		eventMux: eventMux,
		events:   eventMux.Subscribe(LightChainHeadEvent{}),
		chain:    chain,
		relay:    relay,
		odr:      chain.Odr(),
		chainDb:  chain.Odr().Database(),
		head:     chain.CurrentHeader().Hash(),
		clearIdx: chain.CurrentHeader().GetNumberU64(),
	}
	go pool.eventLoop()

	return pool
}

// currentState returns the light state of the current head header
func (pool *TxPool) currentState() *LightState {
	return NewLightState(StateTrieID(pool.chain.CurrentHeader()), pool.odr)
}

// GetNonce returns the "pending" nonce of a given address. It always queries
// the nonce belonging to the latest header too in order to detect if another
// client using the same key sent a transaction.
func (pool *TxPool) GetNonce(ctx context.Context, addr common.Address) (uint64, error) {
	nonce, err := pool.currentState().GetNonce(ctx, addr)
	if err != nil {
		return 0, err
	}
	sn, ok := pool.nonce[addr]
	if ok && sn > nonce {
		nonce = sn
	}
	if !ok || sn < nonce {
		pool.nonce[addr] = nonce
	}
	return nonce, nil
}

type txBlockData struct {
	BlockHash  common.Hash
	BlockIndex uint64
	Index      uint64
}

// storeTxBlockData stores the block position of a mined tx in the local db
func (pool *TxPool) storeTxBlockData(txh common.Hash, tbd txBlockData) {
	data, _ := rlp.EncodeToBytes(tbd)
	pool.chainDb.Put(append(txh[:], byte(1)), data)
}

// removeTxBlockData removes the stored block position of a rolled back tx
func (pool *TxPool) removeTxBlockData(txh common.Hash) {
	pool.chainDb.Delete(append(txh[:], byte(1)))
}

// txStateChanges stores the recent changes between pending/mined states of
// transactions. True means mined, false means rolled back, no entry means no change
type txStateChanges map[common.Hash]bool

// setState sets the status of a tx to either recently mined or recently rolled back
func (txc txStateChanges) setState(txHash common.Hash, mined bool) {
	val, ent := txc[txHash]
	if ent && (val != mined) {
		delete(txc, txHash)
	} else {
		txc[txHash] = mined
	}
}

// getLists creates lists of mined and rolled back tx hashes
func (txc txStateChanges) getLists() (mined []common.Hash, rollback []common.Hash) {
	for hash, val := range txc {
		if val {
			mined = append(mined, hash)
		} else {
			rollback = append(rollback, hash)
		}
	}
	return
}

// checkMinedTxs checks newly added blocks for the currently pending transactions
// and marks them as mined if necessary. It also stores block position in the db
// and adds them to the received txStateChanges map.
func (pool *TxPool) checkMinedTxs(ctx context.Context, hash common.Hash, idx uint64, txc txStateChanges) error {
	if len(pool.pending) == 0 {
		return nil
	}

	receipts, err := GetBlockReceipts(ctx, pool.odr, hash)
	if err != nil {
		return err
	}
	list := pool.mined[hash]
	for i, receipt := range receipts {
		txHash := receipt.TxHash
		if tx, ok := pool.pending[txHash]; ok {
			pool.storeTxBlockData(txHash, txBlockData{hash, idx, uint64(i)})
			delete(pool.pending, txHash)
			list = append(list, tx)
			txc.setState(txHash, true)
		}
	}
	if list != nil {
		pool.mined[hash] = list
	}
	return nil
}

// rollbackTxs marks the transactions contained in recently rolled back blocks
// as rolled back. It also removes block position info from the db and adds them
// to the received txStateChanges map.
func (pool *TxPool) rollbackTxs(hash common.Hash, txc txStateChanges) {
	if list, ok := pool.mined[hash]; ok {
		for _, tx := range list {
			txHash := tx.Hash()
			pool.removeTxBlockData(txHash)
			pool.pending[txHash] = tx
			txc.setState(txHash, false)
		}
		delete(pool.mined, hash)
	}
}

// setNewHead sets a new head header, processing (and rolling back if necessary)
// the blocks since the last known head and returns a txStateChanges map containing
// the recently mined and rolled back transaction hashes. If an error (context
// timeout) occurs during checking new blocks, it leaves the locally known head
// at the latest checked block and still returns a valid txStateChanges, making it
// possible to continue checking the missing blocks at the next chain head event
func (pool *TxPool) setNewHead(ctx context.Context, newHeader *types.Header) (txStateChanges, error) {
	txc := make(txStateChanges)
	oldh := pool.chain.GetHeader(pool.head)
	newh := newHeader
	// find common ancestor, create list of rolled back and new block hashes
	var oldHashes, newHashes []common.Hash
	for oldh.Hash() != newh.Hash() {
		if oldh.GetNumberU64() >= newh.GetNumberU64() {
			oldHashes = append(oldHashes, oldh.Hash())
			oldh = pool.chain.GetHeader(oldh.ParentHash)
		}
		if oldh.GetNumberU64() < newh.GetNumberU64() {
			newHashes = append(newHashes, newh.Hash())
			newh = pool.chain.GetHeader(newh.ParentHash)
		}
	}
	if oldh.GetNumberU64() < pool.clearIdx {
		pool.clearIdx = oldh.GetNumberU64()
	}
	// roll back old blocks
	for _, hash := range oldHashes {
		pool.rollbackTxs(hash, txc)
	}
	pool.head = oldh.Hash()
	// check mined txs of new blocks (array is in reversed order)
	for i := len(newHashes) - 1; i >= 0; i-- {
		hash := newHashes[i]
		if err := pool.checkMinedTxs(ctx, hash, newHeader.GetNumberU64()-uint64(i), txc); err != nil {
			return txc, err
		}
		pool.head = hash
	}

	// clear old mined tx entries of old blocks
	if idx := newHeader.GetNumberU64(); idx > pool.clearIdx+txPermanent {
		idx2 := idx - txPermanent
		for i := pool.clearIdx; i < idx2; i++ {
			hash := core.GetCanonicalHash(pool.chainDb, i)
			if list, ok := pool.mined[hash]; ok {
				hashes := make([]common.Hash, len(list))
				for i, tx := range list {
					hashes[i] = tx.Hash()
				}
				pool.relay.Discard(hashes)
				delete(pool.mined, hash)
			}
		}
		pool.clearIdx = idx2
	}

	return txc, nil
}

// blockCheckTimeout is the time limit for checking new blocks for mined
// transactions. Checking resumes at the next chain head event if timed out.
const blockCheckTimeout = time.Second * 3

// eventLoop processes chain head events and also notifies the tx relay backend
// about the new head hash and tx state changes
func (pool *TxPool) eventLoop() {
	for ev := range pool.events.Chan() {
		switch ev.Data.(type) {
		case LightChainHeadEvent:
			pool.mu.Lock()
			ctx, _ := context.WithTimeout(context.Background(), blockCheckTimeout)
			head := pool.chain.CurrentHeader()
			txc, _ := pool.setNewHead(ctx, head)
			m, r := txc.getLists()
			pool.relay.NewHead(pool.head, m, r)
			pool.homestead = pool.config.IsHomestead(head.Number)
			pool.mu.Unlock()
		}
	}
}

// Stop stops the light transaction pool
func (pool *TxPool) Stop() {
	close(pool.quit)
	pool.events.Unsubscribe()
	glog.V(logger.Info).Infoln("Transaction pool stopped")
}

// Stats returns the number of currently pending (locally created) transactions
func (pool *TxPool) Stats() (pending int) {
	pool.mu.RLock()
	defer pool.mu.RUnlock()

	pending = len(pool.pending)
	return
}

// validateTx checks whether a transaction is valid according to the consensus rules.
func (pool *TxPool) validateTx(ctx context.Context, tx *types.Transaction) error {
	// Validate sender
	var (
		from common.Address
		err  error
	)

	// Validate the transaction sender and it's sig. Throw
	// if the from fields is invalid.
	if from, err = tx.From(); err != nil {
		return core.ErrInvalidSender
	}

	// Make sure the account exist. Non existent accounts
	// haven't got funds and well therefor never pass.
	currentState := pool.currentState()
	if h, err := currentState.HasAccount(ctx, from); err == nil {
		if !h {
			return core.ErrNonExistentAccount
		}
	} else {
		return err
	}

	// Last but not least check for nonce errors
	if n, err := currentState.GetNonce(ctx, from); err == nil {
		if n > tx.Nonce() {
			return core.ErrNonce
		}
	} else {
		return err
	}

	// Check the transaction doesn't exceed the current
	// block limit gas.
	header := pool.chain.GetHeader(pool.head)
	if header.GasLimit.Cmp(tx.Gas()) < 0 {
		return core.ErrGasLimit
	}

	// Transactions can't be negative. This may never happen
	// using RLP decoded transactions but may occur if you create
	// a transaction using the RPC for example.
	if tx.Value().Cmp(common.Big0) < 0 {
		return core.ErrNegativeValue
	}

	// Transactor should have enough funds to cover the costs
	// cost == V + GP * GL
	if b, err := currentState.GetBalance(ctx, from); err == nil {
		if b.Cmp(tx.Cost()) < 0 {
			return core.ErrInsufficientFunds
		}
	} else {
		return err
	}

	// Should supply enough intrinsic gas
	if tx.Gas().Cmp(core.IntrinsicGas(tx.Data(), core.MessageCreatesContract(tx), pool.homestead)) < 0 {
		return core.ErrIntrinsicGas
	}

	return nil
}

// add validates a new transaction and sets its state pending if processable.
// It also updates the locally stored nonce if necessary.
func (self *TxPool) add(ctx context.Context, tx *types.Transaction) error {
	hash := tx.Hash()

	if self.pending[hash] != nil {
		return fmt.Errorf("Known transaction (%x)", hash[:4])
	}
	err := self.validateTx(ctx, tx)
	if err != nil {
		return err
	}

	if _, ok := self.pending[hash]; !ok {
		self.pending[hash] = tx

		nonce := tx.Nonce() + 1
		addr, _ := tx.From()
		if nonce > self.nonce[addr] {
			self.nonce[addr] = nonce
		}

		// Notify the subscribers. This event is posted in a goroutine
		// because it's possible that somewhere during the post "Remove transaction"
		// gets called which will then wait for the global tx pool lock and deadlock.
		go self.eventMux.Post(core.TxPreEvent{tx})
	}

	if glog.V(logger.Debug) {
		var toname string
		if to := tx.To(); to != nil {
			toname = common.Bytes2Hex(to[:4])
		} else {
			toname = "[NEW_CONTRACT]"
		}
		// we can ignore the error here because From is
		// verified in ValidateTransaction.
		f, _ := tx.From()
		from := common.Bytes2Hex(f[:4])
		glog.Infof("(t) %x => %s (%v) %x\n", from, toname, tx.Value, hash)
	}

	return nil
}

// Add adds a transaction to the pool if valid and passes it to the tx relay
// backend
func (self *TxPool) Add(ctx context.Context, tx *types.Transaction) error {
	self.mu.Lock()
	defer self.mu.Unlock()

	data, err := rlp.EncodeToBytes(tx)
	if err != nil {
		return err
	}

	if err := self.add(ctx, tx); err != nil {
		return err
	}
	self.relay.Send(types.Transactions{tx})

	self.chainDb.Put(tx.Hash().Bytes(), data)
	return nil
}

// AddTransactions adds all valid transactions to the pool and passes them to
// the tx relay backend
func (self *TxPool) AddTransactions(ctx context.Context, txs []*types.Transaction) {
	self.mu.Lock()
	defer self.mu.Unlock()
	var sendTx types.Transactions

	for _, tx := range txs {
		if err := self.add(ctx, tx); err != nil {
			glog.V(logger.Debug).Infoln("tx error:", err)
		} else {
			sendTx = append(sendTx, tx)
			h := tx.Hash()
			glog.V(logger.Debug).Infof("tx %x\n", h[:4])
		}
	}

	if len(sendTx) > 0 {
		self.relay.Send(sendTx)
	}
}

// GetTransaction returns a transaction if it is contained in the pool
// and nil otherwise.
func (tp *TxPool) GetTransaction(hash common.Hash) *types.Transaction {
	// check the txs first
	if tx, ok := tp.pending[hash]; ok {
		return tx
	}
	return nil
}

// GetTransactions returns all currently processable transactions.
// The returned slice may be modified by the caller.
func (self *TxPool) GetTransactions() (txs types.Transactions) {
	self.mu.Lock()
	defer self.mu.Unlock()

	txs = make(types.Transactions, len(self.pending))
	i := 0
	for _, tx := range self.pending {
		txs[i] = tx
		i++
	}
	return txs
}

// RemoveTransactions removes all given transactions from the pool.
func (self *TxPool) RemoveTransactions(txs types.Transactions) {
	self.mu.Lock()
	defer self.mu.Unlock()
	var hashes []common.Hash
	for _, tx := range txs {
		//self.RemoveTx(tx.Hash())
		hash := tx.Hash()
		delete(self.pending, hash)
		self.chainDb.Delete(hash[:])
		hashes = append(hashes, hash)
	}
	self.relay.Discard(hashes)
}

// RemoveTx removes the transaction with the given hash from the pool.
func (pool *TxPool) RemoveTx(hash common.Hash) {
	pool.mu.Lock()
	defer pool.mu.Unlock()
	// delete from pending pool
	delete(pool.pending, hash)
	pool.chainDb.Delete(hash[:])
	pool.relay.Discard([]common.Hash{hash})
}