package core

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"sync/atomic"
	"time"

	"github.com/CityOfZion/neo-go/config"
	"github.com/CityOfZion/neo-go/pkg/core/storage"
	"github.com/CityOfZion/neo-go/pkg/core/transaction"
	"github.com/CityOfZion/neo-go/pkg/util"
	log "github.com/sirupsen/logrus"
)

// tuning parameters
const (
	secondsPerBlock  = 15
	headerBatchCount = 2000
	version          = "0.0.1"
)

var (
	genAmount         = []int{8, 7, 6, 5, 4, 3, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1}
	decrementInterval = 2000000
	persistInterval   = 1 * time.Second
)

// Blockchain represents the blockchain.
type Blockchain struct {
	config config.ProtocolConfiguration

	// Any object that satisfies the BlockchainStorer interface.
	storage.Store

	// Current index/height of the highest block.
	// Read access should always be called by BlockHeight().
	// Write access should only happen in persist().
	blockHeight uint32

	// Number of headers stored in the chain file.
	storedHeaderCount uint32

	blockCache *Cache

	// All operation on headerList must be called from an
	// headersOp to be routine safe.
	headerList *HeaderHashList

	// Only for operating on the headerList.
	headersOp     chan headersOpFunc
	headersOpDone chan struct{}

	// Whether we will verify received blocks.
	verifyBlocks bool
}

type headersOpFunc func(headerList *HeaderHashList)

// NewBlockchain return a new blockchain object the will use the
// given Store as its underlying storage.
func NewBlockchain(s storage.Store, cfg config.ProtocolConfiguration) (*Blockchain, error) {
	bc := &Blockchain{
		config:        cfg,
		Store:         s,
		headersOp:     make(chan headersOpFunc),
		headersOpDone: make(chan struct{}),
		blockCache:    NewCache(),
		verifyBlocks:  false,
	}
	go bc.run()

	if err := bc.init(); err != nil {
		return nil, err
	}

	return bc, nil
}

func (bc *Blockchain) init() error {
	genesisBlock, err := createGenesisBlock(bc.config)
	if err != nil {
		return err
	}
	bc.headerList = NewHeaderHashList(genesisBlock.Hash())

	// If we could not find the version in the Store, we know that there is nothing stored.
	ver, err := storage.Version(bc.Store)
	if err != nil {
		log.Infof("no storage version found! creating genesis block")
		storage.PutVersion(bc.Store, version)
		return bc.persistBlock(genesisBlock)
	}
	if ver != version {
		return fmt.Errorf("storage version mismatch betweeen %s and %s", version, ver)
	}

	// At this point there was no version found in the storage which
	// implies a creating fresh storage with the version specified
	// and the genesis block as first block.
	log.Infof("restoring blockchain with version: %s", version)

	bHeight, err := storage.CurrentBlockHeight(bc.Store)
	if err != nil {
		return err
	}
	bc.blockHeight = bHeight

	hashes, err := storage.HeaderHashes(bc.Store)
	if err != nil {
		return err
	}

	for _, hash := range hashes {
		if !genesisBlock.Hash().Equals(hash) {
			bc.headerList.Add(hash)
			bc.storedHeaderCount++
		}
	}

	currHeaderHeight, currHeaderHash, err := storage.CurrentHeaderHeight(bc.Store)
	if err != nil {
		return err
	}

	// There is a high chance that the Node is stopped before the next
	// batch of 2000 headers was stored. Via the currentHeaders stored we can sync
	// that with stored blocks.
	if currHeaderHeight > bc.storedHeaderCount {
		hash := currHeaderHash
		targetHash := bc.headerList.Get(bc.headerList.Len() - 1)
		headers := make([]*Header, 0)

		for hash != targetHash {
			header, err := bc.getHeader(hash)
			if err != nil {
				return fmt.Errorf("could not get header %s: %s", hash, err)
			}
			headers = append(headers, header)
			hash = header.PrevHash
		}

		headerSliceReverse(headers)
		if err := bc.AddHeaders(headers...); err != nil {
			return err
		}
	}

	return nil
}

func (bc *Blockchain) run() {
	persistTimer := time.NewTimer(persistInterval)
	for {
		select {
		case op := <-bc.headersOp:
			op(bc.headerList)
			bc.headersOpDone <- struct{}{}
		case <-persistTimer.C:
			go bc.persist()
			persistTimer.Reset(persistInterval)
		}
	}
}

// AddBlock processes the given block and will add it to the cache so it
// can be persisted.
func (bc *Blockchain) AddBlock(block *Block) error {
	if !bc.blockCache.Has(block.Hash()) {
		bc.blockCache.Add(block.Hash(), block)
	}

	headerLen := bc.headerListLen()
	if int(block.Index-1) >= headerLen {
		return nil
	}
	if int(block.Index) == headerLen {
		if bc.verifyBlocks && !block.Verify(false) {
			return fmt.Errorf("block %s is invalid", block.Hash())
		}
		return bc.AddHeaders(block.Header())
	}
	return nil
}

// AddHeaders will process the given headers and add them to the
// HeaderHashList.
func (bc *Blockchain) AddHeaders(headers ...*Header) (err error) {
	var (
		start = time.Now()
		batch = bc.Batch()
	)

	bc.headersOp <- func(headerList *HeaderHashList) {
		for _, h := range headers {
			if int(h.Index-1) >= headerList.Len() {
				err = fmt.Errorf(
					"height of received header %d is higher then the current header %d",
					h.Index, headerList.Len(),
				)
				return
			}
			if int(h.Index) < headerList.Len() {
				continue
			}
			if !h.Verify() {
				err = fmt.Errorf("header %v is invalid", h)
				return
			}
			if err = bc.processHeader(h, batch, headerList); err != nil {
				return
			}
		}

		if batch.Len() > 0 {
			if err = bc.PutBatch(batch); err != nil {
				return
			}
			log.WithFields(log.Fields{
				"headerIndex": headerList.Len() - 1,
				"blockHeight": bc.BlockHeight(),
				"took":        time.Since(start),
			}).Debug("done processing headers")
		}
	}
	<-bc.headersOpDone
	return err
}

// processHeader processes the given header. Note that this is only thread safe
// if executed in headers operation.
func (bc *Blockchain) processHeader(h *Header, batch storage.Batch, headerList *HeaderHashList) error {
	headerList.Add(h.Hash())

	buf := new(bytes.Buffer)
	for int(h.Index)-headerBatchCount >= int(bc.storedHeaderCount) {
		if err := headerList.Write(buf, int(bc.storedHeaderCount), headerBatchCount); err != nil {
			return err
		}
		key := storage.AppendPrefixInt(storage.IXHeaderHashList, int(bc.storedHeaderCount))
		batch.Put(key, buf.Bytes())
		bc.storedHeaderCount += headerBatchCount
		buf.Reset()
	}

	buf.Reset()
	if err := h.EncodeBinary(buf); err != nil {
		return err
	}

	key := storage.AppendPrefix(storage.DataBlock, h.Hash().BytesReverse())
	batch.Put(key, buf.Bytes())
	batch.Put(storage.SYSCurrentHeader.Bytes(), hashAndIndexToBytes(h.Hash(), h.Index))

	return nil
}

// TODO: persistBlock needs some more love, its implemented as in the original
// project. This for the sake of development speed and understanding of what
// is happening here, quite allot as you can see :). If things are wired together
// and all tests are in place, we can make a more optimized and cleaner implementation.
func (bc *Blockchain) persistBlock(block *Block) error {
	var (
		batch        = bc.Batch()
		unspentCoins = make(UnspentCoins)
		accounts     = make(Accounts)
	)

	storeAsBlock(batch, block, 0)
	storeAsCurrentBlock(batch, block)

	for _, tx := range block.Transactions {
		storeAsTransaction(batch, tx, block.Index)

		// Add CoinStateConfirmed for each tx output.
		unspent := make([]CoinState, len(tx.Outputs))
		for i := 0; i < len(tx.Outputs); i++ {
			unspent[i] = CoinStateConfirmed
		}
		unspentCoins[tx.Hash()] = &UnspentCoinState{unspent}

		// Process TX outputs.
		for _, output := range tx.Outputs {
			account, err := accounts.getAndChange(bc.Store, output.ScriptHash)
			if err != nil {
				return err
			}

			if _, ok := account.Balances[output.AssetID]; ok {
				account.Balances[output.AssetID] += output.Amount
			} else {
				account.Balances[output.AssetID] = output.Amount
			}
		}

		// Process TX inputs that are grouped by previous hash.
		for prevHash, inputs := range tx.GroupInputsByPrevHash() {
			prevTX, _, err := bc.GetTransaction(prevHash)
			if err != nil {
				return fmt.Errorf("could not find previous TX: %s", prevHash)
			}
			for _, input := range inputs {
				unspent, err := unspentCoins.getAndChange(bc.Store, input.PrevHash)
				if err != nil {
					return err
				}
				unspent.states[input.PrevIndex] = CoinStateSpent

				prevTXOutput := prevTX.Outputs[input.PrevIndex]
				account, err := accounts.getAndChange(bc.Store, prevTXOutput.ScriptHash)
				if err != nil {
					return err
				}

				account.Balances[prevTXOutput.AssetID] -= prevTXOutput.Amount
			}
		}

		// Process the underlying type of the TX.
		switch tx.Data.(type) {
		case *transaction.RegisterTX:
		case *transaction.IssueTX:
		case *transaction.ClaimTX:
		case *transaction.EnrollmentTX:
		case *transaction.StateTX:
		case *transaction.PublishTX:
		case *transaction.InvocationTX:
			log.Warn("invocation TX but we have no VM, o noo :(")
		}
	}

	// Persist all to storage.
	if err := accounts.commit(batch); err != nil {
		return err
	}
	if err := unspentCoins.commit(batch); err != nil {
		return err
	}
	if err := bc.PutBatch(batch); err != nil {
		return err
	}

	atomic.StoreUint32(&bc.blockHeight, block.Index)
	return nil
}

func (bc *Blockchain) persist() (err error) {
	var (
		start     = time.Now()
		persisted = 0
		lenCache  = bc.blockCache.Len()
	)

	if lenCache == 0 {
		return nil
	}

	bc.headersOp <- func(headerList *HeaderHashList) {
		for i := 0; i < lenCache; i++ {
			if uint32(headerList.Len()) <= bc.BlockHeight() {
				return
			}
			hash := headerList.Get(int(bc.BlockHeight() + 1))
			if block, ok := bc.blockCache.GetBlock(hash); ok {
				if err = bc.persistBlock(block); err != nil {
					log.Warnf("failed to persist blocks: %s", err)
					return
				}
				bc.blockCache.Delete(hash)
				persisted++
			}
		}
	}
	<-bc.headersOpDone

	if persisted > 0 {
		log.WithFields(log.Fields{
			"persisted":    persisted,
			"headerHeight": bc.HeaderHeight(),
			"blockHeight":  bc.BlockHeight(),
			"took":         time.Since(start),
		}).Info("blockchain persist completed")
	}

	return
}

func (bc *Blockchain) headerListLen() (n int) {
	bc.headersOp <- func(headerList *HeaderHashList) {
		n = headerList.Len()
	}
	<-bc.headersOpDone
	return
}

// GetTransaction returns a TX and its height by the given hash.
func (bc *Blockchain) GetTransaction(hash util.Uint256) (*transaction.Transaction, uint32, error) {
	key := storage.AppendPrefix(storage.DataTransaction, hash.BytesReverse())
	b, err := bc.Get(key)
	if err != nil {
		return nil, 0, err
	}
	r := bytes.NewReader(b)

	var height uint32
	if err := binary.Read(r, binary.LittleEndian, &height); err != nil {
		return nil, 0, err
	}

	tx := &transaction.Transaction{}
	if err := tx.DecodeBinary(r); err != nil {
		return nil, 0, err
	}
	return tx, height, nil
}

// GetBlock returns a Block by the given hash.
func (bc *Blockchain) GetBlock(hash util.Uint256) (*Block, error) {
	key := storage.AppendPrefix(storage.DataBlock, hash.BytesReverse())
	b, err := bc.Get(key)
	if err != nil {
		return nil, err
	}
	block, err := NewBlockFromTrimmedBytes(b)
	if err != nil {
		return nil, err
	}
	// TODO: persist TX first before we can handle this logic.
	//if len(block.Transactions) == 0 {
	//	return nil, fmt.Errorf("block has no TX")
	//}
	return block, nil
}

func (bc *Blockchain) getHeader(hash util.Uint256) (*Header, error) {
	b, err := bc.Get(storage.AppendPrefix(storage.DataBlock, hash.BytesReverse()))
	if err != nil {
		return nil, err
	}
	block, err := NewBlockFromTrimmedBytes(b)
	if err != nil {
		return nil, err
	}
	return block.Header(), nil
}

// HasBlock return true if the blockchain contains he given
// transaction hash.
func (bc *Blockchain) HasTransaction(hash util.Uint256) bool {
	return false
}

// HasBlock return true if the blockchain contains the given
// block hash.
func (bc *Blockchain) HasBlock(hash util.Uint256) bool {
	if header, err := bc.getHeader(hash); err == nil {
		return header.Index <= bc.BlockHeight()
	}
	return false
}

// CurrentBlockHash returns the heighest processed block hash.
func (bc *Blockchain) CurrentBlockHash() (hash util.Uint256) {
	bc.headersOp <- func(headerList *HeaderHashList) {
		hash = headerList.Get(int(bc.BlockHeight()))
	}
	<-bc.headersOpDone
	return
}

// CurrentHeaderHash returns the hash of the latest known header.
func (bc *Blockchain) CurrentHeaderHash() (hash util.Uint256) {
	bc.headersOp <- func(headerList *HeaderHashList) {
		hash = headerList.Last()
	}
	<-bc.headersOpDone
	return
}

// GetHeaderHash return the hash from the headerList by its
// height/index.
func (bc *Blockchain) GetHeaderHash(i int) (hash util.Uint256) {
	bc.headersOp <- func(headerList *HeaderHashList) {
		hash = headerList.Get(i)
	}
	<-bc.headersOpDone
	return
}

// BlockHeight returns the height/index of the highest block.
func (bc *Blockchain) BlockHeight() uint32 {
	return atomic.LoadUint32(&bc.blockHeight)
}

// HeaderHeight returns the index/height of the highest header.
func (bc *Blockchain) HeaderHeight() uint32 {
	return uint32(bc.headerListLen() - 1)
}

func hashAndIndexToBytes(h util.Uint256, index uint32) []byte {
	buf := make([]byte, 4)
	binary.LittleEndian.PutUint32(buf, index)
	return append(h.BytesReverse(), buf...)
}