package blockchain

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"github.com/p9c/p9/pkg/block"
	"math/big"
	"sync"
	"time"
	
	"github.com/p9c/p9/pkg/chainhash"
	"github.com/p9c/p9/pkg/database"
	"github.com/p9c/p9/pkg/wire"
)

const (
	// blockHdrSize is the size of a block header. This is simply the constant from wire and is only provided here for
	// convenience since wire.MaxBlockHeaderPayload is quite long.
	blockHdrSize = wire.MaxBlockHeaderPayload
	// latestUtxoSetBucketVersion is the current version of the utxo set bucket that is used to track all unspent
	// outputs.
	latestUtxoSetBucketVersion = 2
	// latestSpendJournalBucketVersion is the current version of the spend journal bucket that is used to track all
	// spent transactions for use in reorgs.
	latestSpendJournalBucketVersion = 1
)

var (
	// blockIndexBucketName is the name of the db bucket used to house to the block headers and contextual information.
	blockIndexBucketName = []byte("blockheaderidx")
	// hashIndexBucketName is the name of the db bucket used to house to the block hash -> block height index.
	hashIndexBucketName = []byte("hashidx")
	// heightIndexBucketName is the name of the db bucket used to house to the block height -> block hash index.
	heightIndexBucketName = []byte("heightidx")
	// chainStateKeyName is the name of the db key used to store the best chain state.
	chainStateKeyName = []byte("chainstate")
	// spendJournalVersionKeyName is the name of the db key used to store the version of the spend journal currently in
	// the database.
	spendJournalVersionKeyName = []byte("spendjournalversion")
	// spendJournalBucketName is the name of the db bucket used to house transactions outputs that are spent in each
	// block.
	spendJournalBucketName = []byte("spendjournal")
	// utxoSetVersionKeyName is the name of the db key used to store the version of the utxo set currently in the
	// database.
	utxoSetVersionKeyName = []byte("utxosetversion")
	// utxoSetBucketName is the name of the db bucket used to house the unspent transaction output set.
	utxoSetBucketName = []byte("utxosetv2")
	// byteOrder is the preferred byte order used for serializing numeric fields for storage in the database.
	byteOrder = binary.LittleEndian
)

// errNotInMainChain signifies that a block hash or height that is not in the main chain was requested.
type errNotInMainChain string

// DBError implements the error interface.
func (e errNotInMainChain) Error() string {
	return string(e)
}

// isNotInMainChainErr returns whether or not the passed error is an errNotInMainChain error.
func isNotInMainChainErr(e error) bool {
	_, ok := e.(errNotInMainChain)
	return ok
}

// errDeserialize signifies that a problem was encountered when
// deserializing data.
type errDeserialize string

// DBError is an implementation of the errors.* interface
func (e errDeserialize) Error() string {
	return string(e)
}

// isDeserializeErr returns whether or not the passed error is an errDeserialize error.
func isDeserializeErr(e error) bool {
	_, ok := e.(errDeserialize)
	return ok
}

// // isDbBucketNotFoundErr returns whether or not the passed error is a
// database.DBError with an error code of database.ErrBucketNotFound.
// func isDbBucketNotFoundErr(// 	e error) bool {
// 	dbErr, ok := err.(database.DBError)
// 	return ok && dbErr.ErrorCode == database.ErrBucketNotFound
// }

// dbFetchVersion fetches an individual version with the given key from the metadata bucket. It is primarily used to
// track versions on entities such as buckets. It returns zero if the provided key does not exist.
func dbFetchVersion(dbTx database.Tx, key []byte) uint32 {
	serialized := dbTx.Metadata().Get(key)
	if serialized == nil {
		return 0
	}
	return byteOrder.Uint32(serialized[:])
}

// dbPutVersion uses an existing database transaction to update the provided key in the metadata bucket to the given
// version. It is primarily used to track versions on entities such as buckets.
func dbPutVersion(dbTx database.Tx, key []byte, version uint32) (e error) {
	var serialized [4]byte
	byteOrder.PutUint32(serialized[:], version)
	return dbTx.Metadata().Put(key, serialized[:])
}

// dbFetchOrCreateVersion uses an existing database transaction to attempt to fetch the provided key from the metadata
// bucket as a version and in the case it doesn't exist it adds the entry with the provided default version and returns
// that.
//
// This is useful during upgrades to automatically handle loading and adding version keys as necessary.
func dbFetchOrCreateVersion(dbTx database.Tx, key []byte, defaultVersion uint32) (uint32, error) {
	version := dbFetchVersion(dbTx, key)
	if version == 0 {
		version = defaultVersion
		e := dbPutVersion(dbTx, key, version)
		if e != nil {
			return 0, e
		}
	}
	return version, nil
}

// The transaction spend journal consists of an entry for each block
// connected to the main chain which contains the transaction outputs the block spends serialized such that the order is the reverse of the order they were spent. This is required because reorganizing the chain necessarily entails disconnecting blocks to get back to the point of the fork which implies unspending all of the transaction outputs that each block previously spent.
// Since the utxo set, by definition,
// only contains unspent transaction outputs, the spent transaction outputs must be resurrected from somewhere.  There is more than one way this could be done, however this is the most straight forward method that does not require having a transaction index and unpruned
// blockchain.
// NOTE: This format is NOT self describing.
// The additional details such as the number of entries (transaction inputs) are expected to come from the block itself and the utxo set (for legacy entries). The rationale in doing this is to save space. This is also the reason the spent outputs are serialized in the reverse order they are spent because later transactions are allowed to spend outputs from earlier ones in the same block.
// The reserved field below used to keep track of the version of the
// containing transaction when the height in the header code was non-zero, however the height is always non-zero now, but keeping the extra reserved field allows backwards compatibility.
// The serialized format is:
//   [<header code><reserved><compressed txout>],...
//   Field                Type     Size
//   header code          VLQ      variable
//   reserved             byte     1
//   compressed txout
//     compressed amount  VLQ      variable
//     compressed script  []byte   variable
// The serialized header code format is:
//   bit 0 - containing transaction is a coinbase
//   bits 1-x - height of the block that contains the spent txout
// Example 1:
// From block 170 in main blockchain.
//    1300320511db93e1dcdb8a016b49840f8c53bc1eb68a382e97b1482ecad7b148a6909a5c
//    <><><------------------------------------------------------------------>
//     | |                                  |
//     | reserved                  compressed txout
//    header code
//  - header code: 0x13 (coinbase, height 9)
//  - reserved: 0x00
//  - compressed txout 0:
//    - 0x32: VLQ-encoded compressed amount for 5000000000 (50 DUO)
//    - 0x05: special script type pay-to-pubkey
//    - 0x11...5c: x-coordinate of the pubkey
// Example 2:
// Adapted from block 100025 in main blockchain.
//    8b99700091f20f006edbc6c4d31bae9f1ccc38538a114bf42de65e868b99700086c64700b2fb57eadf61e106a100a7445a8c3f67898841ec
//    <----><><----------------------------------------------><----><><---------------------------------------------->
//     |    |                         |                        |    |                         |
//     |    reserved         compressed txout                  |    reserved
//     compressed txout
//    header code                                          header code
//  - Last spent output:
//    - header code: 0x8b9970 (not coinbase, height 100024)
//    - reserved: 0x00
//    - compressed txout:
//      - 0x91f20f: VLQ-encoded compressed amount for 34405000000 (344.05 DUO)
//      - 0x00: special script type pay-to-pubkey-hash
//      - 0x6e...86: pubkey hash
//  - Second to last spent output:
//    - header code: 0x8b9970 (not coinbase, height 100024)
//    - reserved: 0x00
//    - compressed txout:
//      - 0x86c647: VLQ-encoded compressed amount for 13761000000 (137.61 DUO)
//      - 0x00: special script type pay-to-pubkey-hash
//      - 0xb2...ec: pubkey hash
// -----------------------------------------------------------------------------

// SpentTxOut contains a spent transaction output and potentially additional contextual information such as whether or
// not it was contained
//
// in a coinbase transaction, the version of the transaction it was contained in, and which block height the containing
// transaction was included in.
//
// As described in the comments above, the additional contextual information will only be valid when this spent txout is
// spending the last unspent output of the containing transaction.
type SpentTxOut struct {
	// Amount is the amount of the output.
	Amount int64
	// PkScipt is the the public key script for the output.
	PkScript []byte
	// Height is the height of the the block containing the creating tx.
	Height int32
	// Denotes if the creating tx is a coinbase.
	IsCoinBase bool
}

// FetchSpendJournal attempts to retrieve the spend journal, or the set of outputs spent for the target block.
//
// This provides a view of all the outputs that will be consumed once the target block is connected to the end of the
// main chain.
//
// This function is safe for concurrent access.
func (b *BlockChain) FetchSpendJournal(targetBlock *block.Block) ([]SpentTxOut, error) {
	b.ChainLock.RLock()
	defer b.ChainLock.RUnlock()
	var spendEntries []SpentTxOut
	e := b.db.View(
		func(dbTx database.Tx) (e error) {
			spendEntries, e = dbFetchSpendJournalEntry(dbTx, targetBlock)
			return e
		},
	)
	if e != nil {
		return nil, e
	}
	return spendEntries, nil
}

// spentTxOutHeaderCode returns the calculated header code to be used when serializing the provided stxo entry.
func spentTxOutHeaderCode(stxo *SpentTxOut) uint64 {
	// As described in the serialization format comments, the header code encodes the height shifted over one bit and
	// the coinbase flag in the lowest bit.
	headerCode := uint64(stxo.Height) << 1
	if stxo.IsCoinBase {
		headerCode |= 0x01
	}
	return headerCode
}

// spentTxOutSerializeSize returns the number of bytes it would take to serialize the passed stxo according to the
// format described above.
func spentTxOutSerializeSize(stxo *SpentTxOut) int {
	size := serializeSizeVLQ(spentTxOutHeaderCode(stxo))
	if stxo.Height > 0 {
		// The legacy v1 spend journal format conditionally tracked the
		// containing transaction version when the height was non-zero,
		// so this is required for backwards compat.
		size += serializeSizeVLQ(0)
	}
	return size + compressedTxOutSize(uint64(stxo.Amount), stxo.PkScript)
}

// putSpentTxOut serializes the passed stxo according to the format described above directly into the passed target byte
// slice.
//
// The target byte slice must be at least large enough to handle the number of bytes returned by the
// SpentTxOutSerializeSize function or it will panic.
func putSpentTxOut(target []byte, stxo *SpentTxOut) int {
	headerCode := spentTxOutHeaderCode(stxo)
	offset := putVLQ(target, headerCode)
	if stxo.Height > 0 {
		// The legacy v1 spend journal format conditionally tracked the containing transaction version when the height
		// was non-zero, so this is required for backwards compat.
		offset += putVLQ(target[offset:], 0)
	}
	return offset + putCompressedTxOut(
		target[offset:], uint64(stxo.Amount),
		stxo.PkScript,
	)
}

// decodeSpentTxOut decodes the passed serialized stxo entry, possibly followed by other data, into the passed stxo
// struct. It returns the number of bytes read.
func decodeSpentTxOut(serialized []byte, stxo *SpentTxOut) (int, error) {
	// Ensure there are bytes to decode.
	if len(serialized) == 0 {
		return 0, errDeserialize("no serialized bytes")
	}
	// Deserialize the header code.
	code, offset := deserializeVLQ(serialized)
	if offset >= len(serialized) {
		return offset, errDeserialize(
			"unexpected end of data after header code",
		)
	}
	// Decode the header code. Bit 0 indicates containing transaction is a coinbase. Bits 1-x encode height of
	// containing transaction.
	stxo.IsCoinBase = code&0x01 != 0
	stxo.Height = int32(code >> 1)
	if stxo.Height > 0 {
		// The legacy v1 spend journal format conditionally tracked the containing transaction version when the height
		// was non-zero, so this is required for backwards compat.
		_, bytesRead := deserializeVLQ(serialized[offset:])
		offset += bytesRead
		if offset >= len(serialized) {
			return offset, errDeserialize(
				"unexpected end of data after reserved",
			)
		}
	}
	// Decode the compressed txout.
	amount, pkScript, bytesRead, e := decodeCompressedTxOut(
		serialized[offset:],
	)
	offset += bytesRead
	if e != nil {
		return offset, errDeserialize(
			fmt.Sprint(
				"unable to decode txout: ", e,
			),
		)
	}
	stxo.Amount = int64(amount)
	stxo.PkScript = pkScript
	return offset, nil
}

// deserializeSpendJournalEntry decodes the passed serialized byte slice into a slice of spent txouts according to the
// format described in detail above.
//
// Since the serialization format is not self describing as noted in the format comments this function also requires the
// transactions that spend the txouts.
func deserializeSpendJournalEntry(serialized []byte, txns []*wire.MsgTx) ([]SpentTxOut, error) {
	// Calculate the total number of stxos.
	var numStxos int
	for _, tx := range txns {
		numStxos += len(tx.TxIn)
	}
	// When a block has no spent txouts there is nothing to serialize.
	if len(serialized) == 0 {
		// Ensure the block actually has no stxos. This should never happen unless there is database corruption or an
		// empty entry erroneously made its way into the database.
		if numStxos != 0 {
			return nil, AssertError(
				fmt.Sprintf(
					"mismatched spend journal serialization - no serialization for expected %d stxos",
					numStxos,
				),
			)
		}
		return nil, nil
	}
	// Loop backwards through all transactions so everything is read in reverse order to match the serialization order.
	stxoIdx := numStxos - 1
	offset := 0
	stxos := make([]SpentTxOut, numStxos)
	for txIdx := len(txns) - 1; txIdx > -1; txIdx-- {
		tx := txns[txIdx]
		// Loop backwards through all of the transaction inputs and read the associated stxo.
		for txInIdx := len(tx.TxIn) - 1; txInIdx > -1; txInIdx-- {
			txIn := tx.TxIn[txInIdx]
			stxo := &stxos[stxoIdx]
			stxoIdx--
			n, e := decodeSpentTxOut(serialized[offset:], stxo)
			offset += n
			if e != nil {
				return nil, errDeserialize(
					fmt.Sprintf(
						"unable to decode stxo for %v: %v",
						txIn.PreviousOutPoint, e,
					),
				)
			}
		}
	}
	return stxos, nil
}

// serializeSpendJournalEntry serializes all of the passed spent txouts into a single byte slice according to the format
// described in detail above.
func serializeSpendJournalEntry(stxos []SpentTxOut) []byte {
	if len(stxos) == 0 {
		return nil
	}
	// Calculate the size needed to serialize the entire journal entry.
	var size int
	for i := range stxos {
		size += spentTxOutSerializeSize(&stxos[i])
	}
	serialized := make([]byte, size)
	// Serialize each individual stxo directly into the slice in reverse order one after the other.
	var offset int
	for i := len(stxos) - 1; i > -1; i-- {
		offset += putSpentTxOut(serialized[offset:], &stxos[i])
	}
	return serialized
}

// dbFetchSpendJournalEntry fetches the spend journal entry for the passed block and deserializes it into a slice of
// spent txout entries.
//
// NOTE: Legacy entries will not have the coinbase flag or height set unless it was the final output spend in the
// containing transaction.
//
// It is up to the caller to handle this properly by looking the information up in the utxo set.
func dbFetchSpendJournalEntry(dbTx database.Tx, block *block.Block) ([]SpentTxOut, error) {
	// Exclude the coinbase transaction since it can't spend anything.
	spendBucket := dbTx.Metadata().Bucket(spendJournalBucketName)
	serialized := spendBucket.Get(block.Hash()[:])
	blockTxns := block.WireBlock().Transactions[1:]
	stxos, e := deserializeSpendJournalEntry(serialized, blockTxns)
	if e != nil {
		// Ensure any deserialization errors are returned as database corruption errors.
		if isDeserializeErr(e) {
			return nil, database.DBError{
				ErrorCode: database.ErrCorruption,
				Description: fmt.Sprintf(
					"corrupt spend information for %v: %v",
					block.Hash(), e,
				),
			}
		}
		return nil, e
	}
	return stxos, nil
}

// dbPutSpendJournalEntry uses an existing database transaction to update the spend journal entry for the given block
// hash using the provided slice of spent txouts. The spent txouts slice must contain an entry for every txout the
// transactions in the block spend in the order they are spent.
func dbPutSpendJournalEntry(dbTx database.Tx, blockHash *chainhash.Hash, stxos []SpentTxOut) (e error) {
	spendBucket := dbTx.Metadata().Bucket(spendJournalBucketName)
	serialized := serializeSpendJournalEntry(stxos)
	return spendBucket.Put(blockHash[:], serialized)
}

// dbRemoveSpendJournalEntry uses an existing database transaction to remove the spend journal entry for the passed
// block hash.
func dbRemoveSpendJournalEntry(dbTx database.Tx, blockHash *chainhash.Hash) (e error) {
	spendBucket := dbTx.Metadata().Bucket(spendJournalBucketName)
	return spendBucket.Delete(blockHash[:])
}

// The unspent transaction output (
// utxo) set consists of an entry for each unspent output using a format that is optimized to reduce space using domain specific compression algorithms.  This format is a slightly modified version of the format used in Bitcoin Core.
// Each entry is keyed by an outpoint as specified below.
// It is important to note that the key encoding uses a VLQ, which employs an MSB encoding so iteration of utxos when doing byte-wise comparisons will produce them in order.
// The serialized key format is:
//   <hash><output index>
//   Field                Type             Size
//   hash                 chainhash.Hash   chainhash.HashSize
//   output index         VLQ              variable
// The serialized value format is:
//   <header code><compressed txout>
//   Field                Type     Size
//   header code          VLQ      variable
//   compressed txout
//     compressed amount  VLQ      variable
//     compressed script  []byte   variable
// The serialized header code format is:
//   bit 0 - containing transaction is a coinbase
//   bits 1-x - height of the block that contains the unspent txout
// Example 1:
// From tx in main blockchain:
// Blk 1, 0e3e2357e806b6cdb1f70b54c3a3a17b6714ee1f0e68bebb44a74b1efd512098:0
//    03320496b538e853519c726a2c91e61ec11600ae1390813a627c66fb8be7947be63c52
//    <><------------------------------------------------------------------>
//     |                                          |
//   header code                         compressed txout
//  - header code: 0x03 (coinbase, height 1)
//  - compressed txout:
//    - 0x32: VLQ-encoded compressed amount for 5000000000 (50 DUO)
//    - 0x04: special script type pay-to-pubkey
//    - 0x96...52: x-coordinate of the pubkey
// Example 2:
// From tx in main blockchain:
// Blk 113931,
// 4a16969aa4764dd7507fc1de7f0baa4850a246de90c45e59a3207f9a26b5036f:2
//    8cf316800900b8025be1b3efc63b0ad48e7f9f10e87544528d58
//    <----><------------------------------------------>
//      |                             |
//   header code             compressed txout
//  - header code: 0x8cf316 (not coinbase, height 113931)
//  - compressed txout:
//    - 0x8009: VLQ-encoded compressed amount for 15000000 (0.15 DUO)
//    - 0x00: special script type pay-to-pubkey-hash
//    - 0xb8...58: pubkey hash
// Example 3:
// From tx in main blockchain:
// Blk 338156,
// 1b02d1c8cfef60a189017b9a420c682cf4a0028175f2f563209e4ff61c8c3620:22
//    a8a2588ba5b9e763011dd46a006572d820e448e12d2bbb38640bc718e6
//    <----><-------------------------------------------------->
//      |                             |
//   header code             compressed txout
//  - header code: 0xa8a258 (not coinbase, height 338156)
//  - compressed txout:
//    - 0x8ba5b9e763: VLQ-encoded compressed amount for 366875659 (3.
//    66875659 DUO)
//    - 0x01: special script type pay-to-script-hash
//    - 0x1d...e6: script hash
// -----------------------------------------------------------------------------

// maxUint32VLQSerializeSize is the maximum number of bytes a max uint32 takes to serialize as a VLQ.
var maxUint32VLQSerializeSize = serializeSizeVLQ(1<<32 - 1)

// outpointKeyPool defines a concurrent safe free list of byte slices used to provide temporary buffers for outpoint
// database keys.
var outpointKeyPool = sync.Pool{
	New: func() interface{} {
		b := make([]byte, chainhash.HashSize+maxUint32VLQSerializeSize)
		return &b // Pointer to slice to avoid boxing alloc.
	},
}

// outpointKey returns a key suitable for use as a database key in the utxo set while making use of a free list.
//
// A new buffer is allocated if there are not already any available on the free list. The returned byte slice should be
// returned to the free list by using the recycleOutpointKey function when the caller is done with it _unless_ the slice
// will need to live for longer than the caller can calculate such as when used to write to the database.
func outpointKey(outpoint wire.OutPoint) *[]byte {
	// A VLQ employs an MSB encoding, so they are useful not only to reduce the amount of storage space, but also so
	// iteration of utxos when doing byte-wise comparisons will produce them in order.
	key := outpointKeyPool.Get().(*[]byte)
	idx := uint64(outpoint.Index)
	*key = (*key)[:chainhash.HashSize+serializeSizeVLQ(idx)]
	copy(*key, outpoint.Hash[:])
	putVLQ((*key)[chainhash.HashSize:], idx)
	return key
}

// recycleOutpointKey puts the provided byte slice, which should have been obtained via the outpointKey function, back
// on the free list.
func recycleOutpointKey(key *[]byte) {
	outpointKeyPool.Put(key)
}

// utxoEntryHeaderCode returns the calculated header code to be used when serializing the provided utxo entry.
func utxoEntryHeaderCode(entry *UtxoEntry) (rv uint64, e error) {
	if entry.IsSpent() {
		return 0, AssertError("attempt to serialize spent UXTO header")
	}
	// As described in the serialization format comments, the header code encodes the height shifted over one bit and
	// the coinbase flag in the lowest bit.
	headerCode := uint64(entry.BlockHeight()) << 1
	if entry.IsCoinBase() {
		headerCode |= 0x01
	}
	return headerCode, nil
}

// serializeUtxoEntry returns the entry serialized to a format that is suitable for long-term storage. The format is
// described in detail above.
func serializeUtxoEntry(entry *UtxoEntry) ([]byte, error) {
	// Spent outputs have no serialization.
	if entry.IsSpent() {
		return nil, nil
	}
	// Encode the header code.
	headerCode, e := utxoEntryHeaderCode(entry)
	if e != nil {
		return nil, e
	}
	// Calculate the size needed to serialize the entry.
	size := serializeSizeVLQ(headerCode) +
		compressedTxOutSize(uint64(entry.Amount()), entry.PkScript())
	// Serialize the header code followed by the compressed unspent transaction output.
	serialized := make([]byte, size)
	offset := putVLQ(serialized, headerCode)
	_ = putCompressedTxOut(
		serialized[offset:], uint64(entry.Amount()),
		entry.PkScript(),
	)
	return serialized, nil
}

// deserializeUtxoEntry decodes a utxo entry from the passed serialized byte slice into a new UtxoEntry using a format
// that is suitable for long -term storage. The format is described in detail above.
func deserializeUtxoEntry(serialized []byte) (entry *UtxoEntry, e error) {
	// Deserialize the header code.
	code, offset := deserializeVLQ(serialized)
	if offset >= len(serialized) {
		return nil, errDeserialize("unexpected end of data after header")
	}
	// Decode the header code. Bit 0 indicates whether the containing transaction is a coinbase. Bits 1-x encode height
	// of containing transaction.
	isCoinBase := code&0x01 != 0
	blockHeight := int32(code >> 1)
	// Decode the compressed unspent transaction output.
	var amount uint64
	var pkScript []byte
	amount, pkScript, _, e = decodeCompressedTxOut(serialized[offset:])
	if e != nil {
		return nil, errDeserialize(
			fmt.Sprint(
				"unable to decode utxo:", e,
			),
		)
	}
	entry = &UtxoEntry{
		amount:      int64(amount),
		pkScript:    pkScript,
		blockHeight: blockHeight,
		packedFlags: 0,
	}
	if isCoinBase {
		entry.packedFlags |= tfCoinBase
	}
	return entry, nil
}

// dbFetchUtxoEntryByHash attempts to find and fetch a utxo for the given hash. It uses a cursor and seek to try and do
// this as efficiently as possible. When there are no entries for the provided hash, nil will be returned for the both
// the entry and the error.
func dbFetchUtxoEntryByHash(dbTx database.Tx, hash *chainhash.Hash) (*UtxoEntry, error) {
	// Attempt to find an entry by seeking for the hash along with a zero index. Due to the fact the keys are serialized
	// as <hash><index>, where the index uses an MSB encoding, if there are any entries for the hash at all, one will be
	// found.
	cursor := dbTx.Metadata().Bucket(utxoSetBucketName).Cursor()
	key := outpointKey(wire.OutPoint{Hash: *hash, Index: 0})
	ok := cursor.Seek(*key)
	recycleOutpointKey(key)
	if !ok {
		return nil, nil
	}
	// An entry was found, but it could just be an entry with the next highest hash after the requested one, so make
	// sure the hashes actually match.
	cursorKey := cursor.Key()
	if len(cursorKey) < chainhash.HashSize {
		return nil, nil
	}
	if !bytes.Equal(hash[:], cursorKey[:chainhash.HashSize]) {
		return nil, nil
	}
	return deserializeUtxoEntry(cursor.Value())
}

// dbFetchUtxoEntry uses an existing database transaction to fetch the specified transaction output from the utxo set.
// When there is no entry for the provided output, nil will be returned for both the entry and the error.
func dbFetchUtxoEntry(dbTx database.Tx, outpoint wire.OutPoint) (*UtxoEntry, error) {
	// Fetch the unspent transaction output information for the passed transaction output. Return now when there is no
	// entry.
	key := outpointKey(outpoint)
	utxoBucket := dbTx.Metadata().Bucket(utxoSetBucketName)
	serializedUtxo := utxoBucket.Get(*key)
	recycleOutpointKey(key)
	if serializedUtxo == nil {
		return nil, nil
	}
	// A non-nil zero-length entry means there is an entry in the database for a spent transaction output which should
	// never be the case.
	if len(serializedUtxo) == 0 {
		return nil, AssertError(
			fmt.Sprint(
				"database contains entry for spent tx output ",
				outpoint,
			),
		)
	}
	// Deserialize the utxo entry and return it.
	entry, e := deserializeUtxoEntry(serializedUtxo)
	if e != nil {
		// Ensure any deserialization errors are returned as database corruption errors.
		if isDeserializeErr(e) {
			return nil, database.DBError{
				ErrorCode: database.ErrCorruption,
				Description: fmt.Sprintf(
					"corrupt utxo entry for %v: %v",
					outpoint, e,
				),
			}
		}
		return nil, e
	}
	return entry, nil
}

// dbPutUtxoView uses an existing database transaction to update the utxo set in the database based on the provided utxo
// view contents and state.
//
// In particular, only the entries that have been marked as modified are written to the database.
func dbPutUtxoView(dbTx database.Tx, view *UtxoViewpoint) (e error) {
	utxoBucket := dbTx.Metadata().Bucket(utxoSetBucketName)
	for outpoint, entry := range view.entries {
		// No need to update the database if the entry was not modified.
		if entry == nil || !entry.isModified() {
			continue
		}
		// Remove the utxo entry if it is spent.
		if entry.IsSpent() {
			key := outpointKey(outpoint)
			e := utxoBucket.Delete(*key)
			recycleOutpointKey(key)
			if e != nil {
				return e
			}
			continue
		}
		// Serialize and store the utxo entry.
		serialized, e := serializeUtxoEntry(entry)
		if e != nil {
			return e
		}
		key := outpointKey(outpoint)
		e = utxoBucket.Put(*key, serialized)
		// NOTE: The key is intentionally not recycled here since the database interface contract prohibits
		// modifications. It will be garbage collected normally when the database is done with it.
		if e != nil {
			return e
		}
	}
	return nil
}

// The block index consists of two buckets with an entry for every block in
// the main chain.  One bucket is for the hash to height mapping and the other is for the height to hash mapping.
// The serialized format for values in the hash to height bucket is:
//   <height>
//   Field      Type     Size
//   height     uint32   4 bytes
// The serialized format for values in the height to hash bucket is:
//   <hash>
//   Field      Type             Size
//   hash       chainhash.Hash   chainhash.HashSize
// -----------------------------------------------------------------------------

// dbPutBlockIndex uses an existing database transaction to update or add the block index entries for the hash to height
// and height to hash mappings for the provided values.
func dbPutBlockIndex(dbTx database.Tx, hash *chainhash.Hash, height int32) (e error) {
	// Serialize the height for use in the index entries.
	var serializedHeight [4]byte
	byteOrder.PutUint32(serializedHeight[:], uint32(height))
	// Add the block hash to height mapping to the index.
	meta := dbTx.Metadata()
	hashIndex := meta.Bucket(hashIndexBucketName)
	if e := hashIndex.Put(hash[:], serializedHeight[:]); E.Chk(e) {
		return e
	}
	// Add the block height to hash mapping to the index.
	heightIndex := meta.Bucket(heightIndexBucketName)
	return heightIndex.Put(serializedHeight[:], hash[:])
}

// dbRemoveBlockIndex uses an existing database transaction remove block index entries from the hash to height and
// height to hash mappings for the provided values.
func dbRemoveBlockIndex(dbTx database.Tx, hash *chainhash.Hash, height int32) (e error) {
	// Remove the block hash to height mapping.
	meta := dbTx.Metadata()
	hashIndex := meta.Bucket(hashIndexBucketName)
	if e := hashIndex.Delete(hash[:]); E.Chk(e) {
		return e
	}
	// Remove the block height to hash mapping.
	var serializedHeight [4]byte
	byteOrder.PutUint32(serializedHeight[:], uint32(height))
	heightIndex := meta.Bucket(heightIndexBucketName)
	return heightIndex.Delete(serializedHeight[:])
}

// dbFetchHeightByHash uses an existing database transaction to retrieve the height for the provided hash from the
// index.
func dbFetchHeightByHash(dbTx database.Tx, hash *chainhash.Hash) (int32, error) {
	meta := dbTx.Metadata()
	hashIndex := meta.Bucket(hashIndexBucketName)
	serializedHeight := hashIndex.Get(hash[:])
	if serializedHeight == nil {
		str := fmt.Sprintf(
			"dbFetchHeightByHash: block %s is not in the main chain", hash,
		)
		return 0, errNotInMainChain(str)
	}
	return int32(byteOrder.Uint32(serializedHeight)), nil
}

// dbFetchHashByHeight uses an existing database transaction to retrieve the hash for the provided height from the
// index.
func dbFetchHashByHeight(dbTx database.Tx, height int32) (*chainhash.Hash, error) {
	var serializedHeight [4]byte
	byteOrder.PutUint32(serializedHeight[:], uint32(height))
	meta := dbTx.Metadata()
	heightIndex := meta.Bucket(heightIndexBucketName)
	hashBytes := heightIndex.Get(serializedHeight[:])
	if hashBytes == nil {
		str := fmt.Sprintf(
			"no block at height %d exists", height,
		)
		return nil, errNotInMainChain(str)
	}
	var hash chainhash.Hash
	copy(hash[:], hashBytes)
	return &hash, nil
}

// The best chain state consists of the best block hash and height, the total number of transactions up to and including
// those in the best block, and the accumulated work sum up to and including the best block.
//
// The serialized format is:
//
//   <block hash><block height><total txns><work sum length><work sum>
//   Field             Type             Size
//   block hash        chainhash.Hash   chainhash.HashSize
//   block height      uint32           4 bytes
//   total txns        uint64           8 bytes
//   work sum length   uint32           4 bytes
//   work sum          big.Int          work sum length
// -----------------------------------------------------------------------------

// bestChainState represents the data to be stored the database for the current best chain state.
type bestChainState struct {
	hash      chainhash.Hash
	height    uint32
	totalTxns uint64
	workSum   *big.Int
}

// serializeBestChainState returns the serialization of the passed block best chain state. This is data to be stored in
// the chain state bucket.
func serializeBestChainState(state bestChainState) []byte {
	// Calculate the full size needed to serialize the chain state.
	workSumBytes := state.workSum.Bytes()
	workSumBytesLen := uint32(len(workSumBytes))
	serializedLen := chainhash.HashSize + 4 + 8 + 4 + workSumBytesLen
	// Serialize the chain state.
	serializedData := make([]byte, serializedLen)
	copy(serializedData[0:chainhash.HashSize], state.hash[:])
	offset := uint32(chainhash.HashSize)
	byteOrder.PutUint32(serializedData[offset:], state.height)
	offset += 4
	byteOrder.PutUint64(serializedData[offset:], state.totalTxns)
	offset += 8
	byteOrder.PutUint32(serializedData[offset:], workSumBytesLen)
	offset += 4
	copy(serializedData[offset:], workSumBytes)
	return serializedData[:]
}

// deserializeBestChainState deserializes the passed serialized best chain state. This is data stored in the chain state
// bucket and is updated after every block is connected or disconnected form the main chain. block.
func deserializeBestChainState(serializedData []byte) (bestChainState, error) {
	// Ensure the serialized data has enough bytes to properly deserialize the hash, height, total transactions, and
	// work sum length.
	if len(serializedData) < chainhash.HashSize+16 {
		return bestChainState{}, database.DBError{
			ErrorCode:   database.ErrCorruption,
			Description: "corrupt best chain state",
		}
	}
	state := bestChainState{}
	copy(state.hash[:], serializedData[0:chainhash.HashSize])
	offset := uint32(chainhash.HashSize)
	state.height = byteOrder.Uint32(serializedData[offset : offset+4])
	offset += 4
	state.totalTxns = byteOrder.Uint64(serializedData[offset : offset+8])
	offset += 8
	workSumBytesLen := byteOrder.Uint32(serializedData[offset : offset+4])
	offset += 4
	// Ensure the serialized data has enough bytes to deserialize the work sum.
	if uint32(len(serializedData[offset:])) < workSumBytesLen {
		return bestChainState{}, database.DBError{
			ErrorCode:   database.ErrCorruption,
			Description: "corrupt best chain state",
		}
	}
	workSumBytes := serializedData[offset : offset+workSumBytesLen]
	state.workSum = new(big.Int).SetBytes(workSumBytes)
	return state, nil
}

// dbPutBestState uses an existing database transaction to update the best chain state with the given parameters.
func dbPutBestState(dbTx database.Tx, snapshot *BestState, workSum *big.Int) (e error) {
	// Serialize the current best chain state.
	serializedData := serializeBestChainState(
		bestChainState{
			hash:      snapshot.Hash,
			height:    uint32(snapshot.Height),
			totalTxns: snapshot.TotalTxns,
			workSum:   workSum,
		},
	)
	// Store the current best chain state into the database.
	return dbTx.Metadata().Put(chainStateKeyName, serializedData)
}

// createChainState initializes both the database and the chain state to the genesis block. This includes creating the
// necessary buckets and inserting the genesis block so it must only be called on an uninitialized database.
func (b *BlockChain) createChainState() (e error) {
	// Create a new node from the genesis block and set it as the best node.
	genesisBlock := block.NewBlock(b.params.GenesisBlock)
	// Tracec(func() string {
	//	xx, _ := genesisBlock.Bytes()
	//	return hex.EncodeToString(xx)
	// })
	genesisBlock.SetHeight(0)
	header := &genesisBlock.WireBlock().Header
	node := NewBlockNode(header, nil)
	node.status = statusDataStored | statusValid
	var df Diffs
	df, e = b.CalcNextRequiredDifficultyPlan9Controller(node)
	node.Diffs.Store(df)
	if e != nil {
	}
	b.BestChain.SetTip(node)
	// Add the new node to the index which is used for faster lookups.
	b.Index.addNode(node)
	// Initialize the state related to the best block. Since it is the genesis block, use its timestamp for the median
	// time.
	numTxns := uint64(len(genesisBlock.WireBlock().Transactions))
	blockSize := uint64(genesisBlock.WireBlock().SerializeSize())
	blockWeight := uint64(GetBlockWeight(genesisBlock))
	b.stateSnapshot = newBestState(
		node, blockSize, blockWeight, numTxns,
		numTxns, time.Unix(node.timestamp, 0),
	)
	// Create the initial the database chain state including creating the necessary index buckets and inserting the
	// genesis block.
	e = b.db.Update(
		func(dbTx database.Tx) (e error) {
			meta := dbTx.Metadata()
			// Create the bucket that houses the block index data.
			_, e = meta.CreateBucket(blockIndexBucketName)
			if e != nil {
				return e
			}
			// Create the bucket that houses the chain block hash to height index.
			_, e = meta.CreateBucket(hashIndexBucketName)
			if e != nil {
				return e
			}
			// Create the bucket that houses the chain block height to hash index.
			_, e = meta.CreateBucket(heightIndexBucketName)
			if e != nil {
				return e
			}
			// Create the bucket that houses the spend journal data and store its
			// version.
			_, e = meta.CreateBucket(spendJournalBucketName)
			if e != nil {
				return e
			}
			e = dbPutVersion(
				dbTx, utxoSetVersionKeyName,
				latestUtxoSetBucketVersion,
			)
			if e != nil {
				return e
			}
			// Create the bucket that houses the utxo set and store its version. Note that the genesis block coinbase
			// transaction is intentionally not inserted here since it is not spendable by consensus rules.
			_, e = meta.CreateBucket(utxoSetBucketName)
			if e != nil {
				return e
			}
			e = dbPutVersion(
				dbTx, spendJournalVersionKeyName,
				latestSpendJournalBucketVersion,
			)
			if e != nil {
				return e
			}
			// Save the genesis block to the block index database.
			e = dbStoreBlockNode(dbTx, node)
			if e != nil {
				return e
			}
			// Add the genesis block hash to height and height to hash mappings to the index.
			e = dbPutBlockIndex(dbTx, &node.hash, node.height)
			if e != nil {
				return e
			}
			// Store the current best chain state into the database.
			node.workSum = CalcWork(node.bits, node.height, node.version)
			e = dbPutBestState(dbTx, b.stateSnapshot, node.workSum)
			if e != nil {
				return e
			}
			// Store the genesis block into the database.
			return dbStoreBlock(dbTx, genesisBlock)
		},
	)
	return e
}

// initChainState attempts to load and initialize the chain state from the database. When the db does not yet contain
// any chain state, both it and the chain state are initialized to the genesis block.
func (b *BlockChain) initChainState() (e error) {
	// Determine the state of the chain database. We may need to initialize everything from scratch or upgrade certain
	// buckets.
	var initialized, hasBlockIndex bool
	e = b.db.View(
		func(dbTx database.Tx) (e error) {
			initialized = dbTx.Metadata().Get(chainStateKeyName) != nil
			hasBlockIndex = dbTx.Metadata().Bucket(blockIndexBucketName) != nil
			return nil
		},
	)
	if e != nil {
		return e
	}
	if !initialized {
		// At this point the database has not already been initialized, so initialize both it and the chain state to the
		// genesis block.
		return b.createChainState()
	}
	if !hasBlockIndex {
		e = migrateBlockIndex(b.db)
		if e != nil {
			return nil
		}
	}
	// Attempt to load the chain state from the database.
	e = b.db.View(
		func(dbTx database.Tx) (e error) {
			// Fetch the stored chain state from the database metadata. When it doesn't exist, it means the database hasn't
			// been initialized for use with chain yet, so break out now to allow that to happen under a writable database
			// transaction.
			serializedData := dbTx.Metadata().Get(chainStateKeyName)
			T.F("serialized chain state: %0x", serializedData)
			state, e := deserializeBestChainState(serializedData)
			if e != nil {
				return e
			}
			// Load all of the headers from the data for the known best chain and construct the blk index accordingly.
			// Since the number of nodes are already known, perform a single alloc for them versus a whole bunch of little
			// ones to reduce pressure on the GC.
			T.Ln("loading blk index...")
			blockIndexBucket := dbTx.Metadata().Bucket(blockIndexBucketName)
			// Determine how many blocks will be loaded into the index so we can allocate the right amount.
			var blockCount int32
			cursor := blockIndexBucket.Cursor()
			for ok := cursor.First(); ok; ok = cursor.Next() {
				blockCount++
			}
			blockNodes := make([]BlockNode, blockCount)
			var i int32
			var lastNode *BlockNode
			cursor = blockIndexBucket.Cursor()
			for ok := cursor.First(); ok; ok = cursor.Next() {
				var header *wire.BlockHeader
				var status blockStatus
				header, status, e = deserializeBlockRow(cursor.Value())
				if e != nil {
					return e
				}
				// Determine the parent blk node. Since we iterate blk headers in order of height, if the blocks are
				// mostly linear there is a very good chance the previous header processed is the parent.
				var parent *BlockNode
				if lastNode == nil {
					blockHash := header.BlockHash()
					if !blockHash.IsEqual(b.params.GenesisHash) {
						return AssertError(
							fmt.Sprintf(
								"initChainState: expected first entry in blk index"+
									" to be genesis blk, found %s",
								blockHash,
							),
						)
					}
				} else if header.PrevBlock == lastNode.hash {
					// Since we iterate blk headers in order of height, if the blocks are mostly linear there is a very
					// good chance the previous header processed is the parent.
					parent = lastNode
				} else {
					parent = b.Index.LookupNode(&header.PrevBlock)
					if parent == nil {
						return AssertError(
							fmt.Sprint(
								"initChainState: Could not find parent for blk ",
								header.BlockHash(),
							),
						)
					}
				}
				// Initialize the blk node for the blk, connect it, and add it to the blk index.
				node := &blockNodes[i]
				initBlockNode(node, header, parent)
				node.status = status
				b.Index.addNode(node)
				lastNode = node
				i++
			}
			// Set the best chain view to the stored best state.
			tip := b.Index.LookupNode(&state.hash)
			if tip == nil {
				return AssertError(
					fmt.Sprintf(
						"initChainState: cannot find chain tip %s in blk index",
						state.hash,
					),
				)
			}
			b.BestChain.SetTip(tip)
			// Load the raw blk bytes for the best blk.
			blockBytes, e := dbTx.FetchBlock(&state.hash)
			if e != nil {
				return e
			}
			var blk wire.Block
			e = blk.Deserialize(bytes.NewReader(blockBytes))
			if e != nil {
				return e
			}
			// As a final consistency check, we'll run through all the nodes which are ancestors of the current chain tip,
			// and mark them as valid if they aren't already marked as such. This is a safe assumption as all the blk
			// before the current tip are valid by definition.
			for iterNode := tip; iterNode != nil; iterNode = iterNode.parent {
				// If this isn't already marked as valid in the index, then we'll mark it as valid now to ensure consistency
				// once we 're up and running.
				if !iterNode.status.KnownValid() {
					I.F(
						"Block %v (height=%v) ancestor of chain tip not"+
							" marked as valid, upgrading to valid for consistency",
						iterNode.hash, iterNode.height,
					)
					b.Index.SetStatusFlags(iterNode, statusValid)
				}
			}
			// Initialize the state related to the best blk.
			blockSize := uint64(len(blockBytes))
			blockWeight := uint64(GetBlockWeight(block.NewBlock(&blk)))
			numTxns := uint64(len(blk.Transactions))
			b.stateSnapshot = newBestState(
				tip, blockSize, blockWeight,
				numTxns, state.totalTxns, tip.CalcPastMedianTime(),
			)
			return nil
		},
	)
	if e != nil {
		return e
	}
	// As we might have updated the index after it was loaded, we'll attempt to flush the index to the DB. This will
	// only result in a write if the elements are dirty, so it'll usually be a noop.
	return b.Index.flushToDB()
}

// deserializeBlockRow parses a value in the block index bucket into a block header and block status bitfield.
func deserializeBlockRow(blockRow []byte) (*wire.BlockHeader, blockStatus, error) {
	buffer := bytes.NewReader(blockRow)
	var header wire.BlockHeader
	e := header.Deserialize(buffer)
	if e != nil {
		return nil, statusNone, e
	}
	statusByte, e := buffer.ReadByte()
	if e != nil {
		return nil, statusNone, e
	}
	return &header, blockStatus(statusByte), nil
}

// dbFetchHeaderByHash uses an existing database transaction to retrieve the block header for the provided hash.
func dbFetchHeaderByHash(dbTx database.Tx, hash *chainhash.Hash) (*wire.BlockHeader, error) {
	headerBytes, e := dbTx.FetchBlockHeader(hash)
	if e != nil {
		return nil, e
	}
	var header wire.BlockHeader
	e = header.Deserialize(bytes.NewReader(headerBytes))
	if e != nil {
		return nil, e
	}
	return &header, nil
}

/*// dbFetchHeaderByHeight uses an existing database transaction to retrieve
the block header for the provided height.
func dbFetchHeaderByHeight(dbTx database.Tx,
height int32) (*wire.BlockHeader, error) {
	hash, e := dbFetchHashByHeight(dbTx, height)
	if e != nil  {
		return nil, e
	}
	return dbFetchHeaderByHash(dbTx, hash)
} */

// dbFetchBlockByNode uses an existing database transaction to retrieve the raw block for the provided node, deserialize
// it, and return a util.Block with the height set.
func dbFetchBlockByNode(dbTx database.Tx, node *BlockNode) (*block.Block, error) {
	// Load the raw block bytes from the database.
	blockBytes, e := dbTx.FetchBlock(&node.hash)
	if e != nil {
		return nil, e
	}
	// Create the encapsulated block and set the height appropriately.
	block, e := block.NewFromBytes(blockBytes)
	if e != nil {
		return nil, e
	}
	block.SetHeight(node.height)
	return block, nil
}

// dbStoreBlockNode stores the block header and validation status to the block index bucket. This overwrites the current
// entry if there exists one.
func dbStoreBlockNode(dbTx database.Tx, node *BlockNode) (e error) {
	// Serialize block data to be stored.
	w := bytes.NewBuffer(make([]byte, 0, blockHdrSize+1))
	header := node.Header()
	e = header.Serialize(w)
	if e != nil {
		return e
	}
	e = w.WriteByte(byte(node.status))
	if e != nil {
		return e
	}
	value := w.Bytes()
	// Write block header data to block index bucket.
	blockIndexBucket := dbTx.Metadata().Bucket(blockIndexBucketName)
	key := blockIndexKey(&node.hash, uint32(node.height))
	return blockIndexBucket.Put(key, value)
}

// dbStoreBlock stores the provided block in the database if it is not already there. The full block data is written to
// ffldb.
func dbStoreBlock(dbTx database.Tx, block *block.Block) (e error) {
	hasBlock, e := dbTx.HasBlock(block.Hash())
	if e != nil {
		return e
	}
	if hasBlock {
		return nil
	}
	return dbTx.StoreBlock(block)
}

// blockIndexKey generates the binary key for an entry in the block index bucket. The key is composed of the block
// height encoded as a big-endian 32 -bit unsigned int followed by the 32 byte block hash.
func blockIndexKey(blockHash *chainhash.Hash, blockHeight uint32) []byte {
	indexKey := make([]byte, chainhash.HashSize+4)
	binary.BigEndian.PutUint32(indexKey[0:4], blockHeight)
	copy(indexKey[4:chainhash.HashSize+4], blockHash[:])
	return indexKey
}

// BlockByHeight returns the block at the given height in the main chain. This function is safe for concurrent access.
func (b *BlockChain) BlockByHeight(blockHeight int32) (*block.Block, error) {
	// Lookup the block height in the best chain.
	node := b.BestChain.NodeByHeight(blockHeight)
	if node == nil {
		str := fmt.Sprintf("no block at height %d exists", blockHeight)
		return nil, errNotInMainChain(str)
	}
	// Load the block from the database and return it.
	var block *block.Block
	e := b.db.View(
		func(dbTx database.Tx) (e error) {
			block, e = dbFetchBlockByNode(dbTx, node)
			return e
		},
	)
	return block, e
}

// BlockByHash returns the block from the main chain with the given hash with the appropriate chain height set.
//
// This function is safe for concurrent access.
func (b *BlockChain) BlockByHash(hash *chainhash.Hash) (block *block.Block, e error) {
	// Lookup the block hash in block index and ensure it is in the best chain.
	node := b.Index.LookupNode(hash)
	if node == nil || !b.BestChain.Contains(node) {
		str := fmt.Sprintf("blockByHash: block %s is not in the main chain", hash)
		return nil, errNotInMainChain(str)
	}
	// Load the block from the database and return it.
	e = b.db.View(
		func(dbTx database.Tx) (er error) {
			block, e = dbFetchBlockByNode(dbTx, node)
			return er
		},
	)
	return block, e
}