lbcwallet/txstore/tx.go

/*
 * Copyright (c) 2013, 2014 Conformal Systems LLC <info@conformal.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

package txstore

import (
	"errors"
	"fmt"
	"sort"
	"time"

	"github.com/conformal/btcchain"
	"github.com/conformal/btcnet"
	"github.com/conformal/btcscript"
	"github.com/conformal/btcutil"
	"github.com/conformal/btcwire"
)

var (
	// ErrDuplicateInsert describes the error where an insert was ignored
	// for being a duplicate.
	ErrDuplicateInsert = errors.New("duplicate insert")

	// ErrInconsistentStore describes an error where the transaction store
	// is in an inconsistent state.  This error is unrecoverable, and the
	// transaction store should be regenerated by a rescan.
	ErrInconsistentStore = errors.New("inconsistant transaction store")

	// ErrUnsupportedVersion represents an error where a serialized
	// object is marked with a version that is no longer supported
	// during deserialization.
	ErrUnsupportedVersion = errors.New("version no longer supported")
)

// MissingValueError is a catch-all error interface for any error due to a
// missing value in the transaction store.
type MissingValueError interface {
	Error() string
	MissingValueError() error
}

// MissingBlockError describes an error where a block could not be found in
// the transaction store.  The value is the height of the missing block.
type MissingBlockError int32

// Error implements the error interface.
func (e MissingBlockError) Error() string {
	return fmt.Sprintf("missing record for block %d", e)
}

// MissingValueError implements the MissingValueError interface.
func (e MissingBlockError) MissingValueError() error {
	return e
}

// MissingBlockTxError describes an error where a mined transaction could
// not be found in the transaction store.  The value is the lookup key for
// the mined transaction.
type MissingBlockTxError BlockTxKey

// Error implements the error interface.
func (e MissingBlockTxError) Error() string {
	return fmt.Sprintf("missing record for transaction at block %d index "+
		"%d", e.BlockHeight, e.BlockIndex)
}

// MissingValueError implements the MissingValueError interface.
func (e MissingBlockTxError) MissingValueError() error {
	return e
}

// MissingDebitsError describes an error where a mined transaction does not
// contain any debiting records.  The value is the lookup key for the mined
// transaction.
type MissingDebitsError BlockTxKey

// Error implements the error interface.
func (e MissingDebitsError) Error() string {
	return fmt.Sprintf("missing record for debits at block %d index %d",
		e.BlockHeight, e.BlockIndex)
}

// MissingValueError implements the MissingValueError interface.
func (e MissingDebitsError) MissingValueError() error {
	return e
}

// MissingCreditError describes an error where a mined transaction does not
// contain a credit record at for some output.  The value is the lookup key
// for the mined transaction's output.
type MissingCreditError BlockOutputKey

// Error implements the error interface.
func (e MissingCreditError) Error() string {
	return fmt.Sprintf("missing record for received transaction output at "+
		"block %d index %d output %d", e.BlockHeight, e.BlockIndex,
		e.OutputIndex)
}

// MissingValueError implements the MissingValueError interface.
func (e MissingCreditError) MissingValueError() error {
	return e
}

// TxRecord is the record type for all transactions in the store.  If the
// transaction is mined, BlockTxKey will be the lookup key for the transaction.
// Otherwise, the embedded BlockHeight will be -1.
type TxRecord struct {
	BlockTxKey
	*txRecord
	s *Store
}

// Block holds details about a block that contains wallet transactions.
type Block struct {
	Hash   btcwire.ShaHash
	Time   time.Time
	Height int32
}

// Debits is the type representing any TxRecord which debits from previous
// wallet transaction outputs.
type Debits struct {
	*TxRecord
}

// Credit is the type representing a transaction output which was spent or
// is still spendable by wallet.  A UTXO is an unspent Credit, but not all
// Credits are UTXOs.
type Credit struct {
	*TxRecord
	OutputIndex uint32
}

// blockAmounts holds the immediately spendable and reward (coinbase) amounts
// as a result of all transactions in a block.
type blockAmounts struct {
	Spendable btcutil.Amount
	Reward    btcutil.Amount
}

// Store implements a transaction store for storing and managing wallet
// transactions.
type Store struct {
	// blocks holds wallet transaction records for each block they appear
	// in.  This is sorted by block height in increasing order.  A separate
	// map is included to lookup indexes for blocks at some height.
	blocks       []*blockTxCollection
	blockIndexes map[int32]uint32

	// unspent is a set of block heights which contain transactions with
	// unspent outputs.
	unspent map[int32]struct{}

	// unconfirmed holds a collection of wallet transactions that have not
	// been mined into a block yet.
	unconfirmed unconfirmedStore
}

// blockTxCollection holds a collection of wallet transactions from exactly one
// block.
type blockTxCollection struct {
	// Block holds the hash, time, and height of the block.
	Block

	// amountDeltas is the net increase or decrease of BTC controllable by
	// wallet addresses due to transactions in this block.  This value only
	// tracks the total amount, not amounts for individual addresses (which
	// this txstore implementation is not aware of).
	amountDeltas blockAmounts

	// txs holds all transaction records for a block, sorted by block index.
	// A separate map is included to lookup indexes for txs at some block
	// index.
	txs       []*txRecord
	txIndexes map[int]uint32

	// unspents maps block indexes of transactions with unspent outputs to
	// their index in the txs slice.
	unspent map[int]uint32
}

// unconfirmedStore stores all unconfirmed transactions managed by the Store.
type unconfirmedStore struct {
	// txs contains all unconfirmed transactions, mapping from their
	// transaction hash to the records.
	txs map[btcwire.ShaHash]*txRecord

	// spentBlockOutPoints maps from spent outputs from mined transaction
	// to the unconfirmed transaction which spends it.  An additional
	// map is included to lookup the output key by its outpoint.
	spentBlockOutPoints    map[BlockOutputKey]*txRecord
	spentBlockOutPointKeys map[btcwire.OutPoint]BlockOutputKey

	// spentUnconfirmed maps from an unconfirmed outpoint to the unconfirmed
	// transaction which spends it.
	spentUnconfirmed map[btcwire.OutPoint]*txRecord

	// previousOutpoints maps all previous outputs to the transaction record
	// of the unconfirmed transaction which spends it.  This is primarly
	// designed to assist with double spend detection without iterating
	// through each value of the txs map.
	previousOutpoints map[btcwire.OutPoint]*txRecord
}

// BlockTxKey is a lookup key for a single mined transaction in the store.
type BlockTxKey struct {
	BlockIndex  int
	BlockHeight int32
}

// BlockOutputKey is a lookup key for a transaction output from a block in the
// store.
type BlockOutputKey struct {
	BlockTxKey
	OutputIndex uint32
}

// txRecord holds all credits and debits created by a transaction's inputs and
// outputs.
type txRecord struct {
	// tx is the transaction that all records in this structure reference.
	tx *btcutil.Tx

	// debit records the debits this transaction creates, or nil if the
	// transaction does not spend any previous credits.
	debits *debits

	// credits holds all records for received transaction outputs from
	// this transaction.
	credits []*credit

	received time.Time
}

// debits records the debits a transaction record makes from previous wallet
// transaction credits.
type debits struct {
	amount btcutil.Amount
	spends []*BlockOutputKey
}

// credit describes a transaction output which was or is spendable by wallet.
type credit struct {
	change  bool
	locked  bool
	spentBy *BlockTxKey // nil if unspent
}

// New allocates and initializes a new transaction store.
func New() *Store {
	return &Store{
		blockIndexes: map[int32]uint32{},
		unspent:      map[int32]struct{}{},
		unconfirmed: unconfirmedStore{
			txs:                    map[btcwire.ShaHash]*txRecord{},
			spentBlockOutPoints:    map[BlockOutputKey]*txRecord{},
			spentBlockOutPointKeys: map[btcwire.OutPoint]BlockOutputKey{},
			spentUnconfirmed:       map[btcwire.OutPoint]*txRecord{},
			previousOutpoints:      map[btcwire.OutPoint]*txRecord{},
		},
	}
}

func (s *Store) lookupBlock(height int32) (*blockTxCollection, error) {
	if i, ok := s.blockIndexes[height]; ok {
		return s.blocks[i], nil
	}
	return nil, MissingBlockError(height)
}

func (s *Store) lookupBlockTx(key BlockTxKey) (*txRecord, error) {
	coll, err := s.lookupBlock(key.BlockHeight)
	if err != nil {
		return nil, err
	}
	if i, ok := coll.txIndexes[key.BlockIndex]; ok {
		return coll.txs[i], nil
	}
	return nil, MissingBlockTxError{key.BlockIndex, key.BlockHeight}
}

func (s *Store) lookupBlockDebits(key BlockTxKey) (*debits, error) {
	r, err := s.lookupBlockTx(key)
	if err != nil {
		return nil, err
	}
	if r.debits == nil {
		return nil, MissingDebitsError(key)
	}
	return r.debits, nil
}

func (r *txRecord) lookupBlockCredit(key BlockOutputKey) (*credit, error) {
	switch {
	case len(r.credits) <= int(key.OutputIndex):
		fallthrough
	case r.credits[key.OutputIndex] == nil:
		return nil, MissingCreditError(key)
	}
	return r.credits[key.OutputIndex], nil
}

func (s *Store) lookupBlockCredit(key BlockOutputKey) (*credit, error) {
	txRecord, err := s.lookupBlockTx(key.BlockTxKey)
	if err != nil {
		return nil, err
	}
	return txRecord.lookupBlockCredit(key)
}

func (s *Store) blockCollectionForInserts(block *Block) *blockTxCollection {
	b, err := s.lookupBlock(block.Height)
	switch e := err.(type) {
	case MissingBlockError:
		b = &blockTxCollection{
			Block:     *block,
			txIndexes: map[int]uint32{},
			unspent:   map[int]uint32{},
		}

		// If this new block cannot be appended to the end of the blocks
		// slice (which would disobey ordering blocks by their height),
		// reslice and update the store's map of block heights to block
		// slice indexes.
		if len(s.blocks) > 0 && s.blocks[len(s.blocks)-1].Height > block.Height {
			i := uint32(len(s.blocks))
			for i != 0 && s.blocks[i-1].Height >= block.Height {
				i--
			}
			detached := s.blocks[i:]
			s.blocks = append(s.blocks[:i], b)
			s.blockIndexes[b.Height] = i
			for i, b := range detached {
				newIndex := uint32(i + len(s.blocks))
				s.blockIndexes[b.Height] = newIndex
			}
			s.blocks = append(s.blocks, detached...)

		} else {
			s.blockIndexes[int32(e)] = uint32(len(s.blocks))
			s.blocks = append(s.blocks, b)
		}
	}
	return b
}

func (c *blockTxCollection) lookupTxRecord(blockIndex int) (*txRecord, uint32, error) {
	if i, ok := c.txIndexes[blockIndex]; ok {
		return c.txs[i], i, nil
	}
	return nil, 0, MissingBlockTxError{blockIndex, c.Block.Height}
}

func (c *blockTxCollection) txRecordForInserts(tx *btcutil.Tx) *txRecord {
	if i, ok := c.txIndexes[tx.Index()]; ok {
		return c.txs[i]
	}
	record := &txRecord{tx: tx}

	// If this new transaction record cannot be appended to the end of the
	// txs slice (which would disobey ordering transactions by their block
	// index), reslice and update the block's map of block indexes to txs
	// slice indexes.
	if len(c.txs) > 0 && c.txs[len(c.txs)-1].Tx().Index() > tx.Index() {
		i := uint32(len(c.txs))
		for i != 0 && c.txs[i-1].Tx().Index() >= tx.Index() {
			i--
		}
		detached := c.txs[i:]
		c.txs = append(c.txs[:i], record)
		c.txIndexes[tx.Index()] = i
		for i, r := range detached {
			newIndex := uint32(i + len(c.txs))
			c.txIndexes[r.Tx().Index()] = newIndex
			if _, ok := c.unspent[r.Tx().Index()]; ok {
				c.unspent[r.Tx().Index()] = newIndex
			}
		}
		c.txs = append(c.txs, detached...)
	} else {
		c.txIndexes[tx.Index()] = uint32(len(c.txs))
		c.txs = append(c.txs, record)
	}
	return record
}

func (s *Store) blockTxRecordForInserts(tx *btcutil.Tx, block *Block) *txRecord {
	return s.blockCollectionForInserts(block).txRecordForInserts(tx)
}

func (u *unconfirmedStore) txRecordForInserts(tx *btcutil.Tx) *txRecord {
	r, ok := u.txs[*tx.Sha()]
	if !ok {
		r = &txRecord{tx: tx}
		u.txs[*tx.Sha()] = r
		for _, input := range r.Tx().MsgTx().TxIn {
			u.previousOutpoints[input.PreviousOutpoint] = r
		}
	}
	return r
}

func (r *txRecord) setDebitsSpends(spends []*BlockOutputKey, tx *btcutil.Tx) error {
	if r.debits.spends != nil {
		if *r.tx.Sha() == *tx.Sha() {
			return ErrDuplicateInsert
		}
		return ErrInconsistentStore
	}
	r.debits.spends = spends
	return nil
}

func (r *txRecord) setCredit(c *credit, index uint32, tx *btcutil.Tx) error {
	if len(r.credits) <= int(index) {
		r.credits = extendCredits(r.credits, index)
	}
	if r.credits[index] != nil {
		if *r.tx.Sha() == *tx.Sha() {
			return ErrDuplicateInsert
		}
		return ErrInconsistentStore
	}

	r.credits[index] = c
	return nil
}

func extendCredits(c []*credit, index uint32) []*credit {
	missing := make([]*credit, int(index+1)-len(c))
	return append(c, missing...)
}

func (s *Store) moveMinedTx(r *txRecord, block *Block) error {
	delete(s.unconfirmed.txs, *r.Tx().Sha())

	// Find collection and insert records.  Error out if there are records
	// saved for this block and index.
	key := BlockTxKey{r.Tx().Index(), block.Height}
	b := s.blockCollectionForInserts(block)
	txIndex := uint32(len(b.txs))
	b.txIndexes[key.BlockIndex] = txIndex
	b.txs = append(b.txs, r)

	for _, input := range r.Tx().MsgTx().TxIn {
		delete(s.unconfirmed.previousOutpoints, input.PreviousOutpoint)

		// For all mined transactions with credits spent by this
		// transaction, remove them from the spentBlockOutPoints map
		// (signifying that there is no longer an unconfirmed
		// transaction which spending that credit), and update the
		// credit's spent by tracking with the block key of the
		// newly-mined transaction.
		prev, ok := s.unconfirmed.spentBlockOutPointKeys[input.PreviousOutpoint]
		if !ok {
			continue
		}
		delete(s.unconfirmed.spentBlockOutPointKeys, input.PreviousOutpoint)
		delete(s.unconfirmed.spentBlockOutPoints, prev)
		rr, err := s.lookupBlockTx(prev.BlockTxKey)
		if err != nil {
			return err
		}
		if len(rr.credits) <= int(prev.OutputIndex) {
			rr.credits = extendCredits(rr.credits, prev.OutputIndex)
		}
		rr.credits[prev.OutputIndex].spentBy = &key
		// debits should already be non-nil
		r.debits.spends = append(r.debits.spends, &prev)
	}

	// For each credit in r, if the credit is spent by another unconfirmed
	// transaction, move the spending transaction from spentUnconfirmed
	// (which signifies a transaction spending another unconfirmed tx) to
	// spentBlockTxs (which signifies an unconfirmed transaction spending a
	// confirmed tx) and modify the mined transaction's record to refer to
	// the credit being spent by an unconfirmed transaction.
	//
	// If the credit is not spent, modify the store's unspent bookkeeping
	// maps to include the credit and increment the amount deltas by the
	// credit's value.
	for i, credit := range r.credits {
		if credit == nil {
			continue
		}
		op := btcwire.NewOutPoint(r.Tx().Sha(), uint32(i))
		outputKey := BlockOutputKey{key, uint32(i)}
		if rr, ok := s.unconfirmed.spentUnconfirmed[*op]; ok {
			delete(s.unconfirmed.spentUnconfirmed, *op)
			s.unconfirmed.spentBlockOutPointKeys[*op] = outputKey
			s.unconfirmed.spentBlockOutPoints[outputKey] = rr
			credit.spentBy = &BlockTxKey{BlockHeight: -1}
		} else if credit.spentBy == nil {
			// Mark entire transaction as containing at least one
			// unspent credit.
			s.unspent[key.BlockHeight] = struct{}{}
			b.unspent[key.BlockIndex] = txIndex

			// Increment spendable amount delta as a result of
			// moving this credit to this block.
			value := r.Tx().MsgTx().TxOut[i].Value
			b.amountDeltas.Spendable += btcutil.Amount(value)
		}
	}

	// If this moved transaction debits from any previous credits, decrement
	// the amount deltas by the total input amount.  Because this
	// transaction was moved from the unconfirmed transaction set, this can
	// never be a coinbase.
	if r.debits != nil {
		b.amountDeltas.Spendable -= r.debits.amount
	}

	return nil
}

// InsertTx records a transaction as belonging to a wallet's transaction
// history.  If block is nil, the transaction is considered unspent, and the
// transaction's index must be unset.  Otherwise, the transaction index must be
// set if a non-nil block is set.
//
// The transaction record is returned.  Credits and debits may be added to the
// transaction by calling methods on the TxRecord.
func (s *Store) InsertTx(tx *btcutil.Tx, block *Block) (*TxRecord, error) {
	// The receive time will be the earlier of now and the block time
	// (if any).
	received := time.Now()

	// Verify that the index of the transaction within the block is
	// set if a block is set, and unset if there is no block.
	index := tx.Index()
	switch {
	case index == btcutil.TxIndexUnknown && block != nil:
		return nil, errors.New("transaction block index unset")
	case index != btcutil.TxIndexUnknown && block == nil:
		return nil, errors.New("transaction block index set")
	}

	// Simply create or return the transaction record if this transaction
	// is unconfirmed.
	if block == nil {
		key := BlockTxKey{BlockHeight: -1}
		r := s.unconfirmed.txRecordForInserts(tx)
		r.received = received
		return &TxRecord{key, r, s}, nil
	}

	// Check if block records already exist for this tx.  If so,
	// we're done.
	key := BlockTxKey{index, block.Height}
	record, err := s.lookupBlockTx(key)
	switch err.(type) {
	case MissingValueError:
		// handle it later
	case nil:
		// Verify that the txs actually match.
		if *record.tx.Sha() != *tx.Sha() {
			return nil, ErrInconsistentStore
		}

		return &TxRecord{key, record, s}, nil
	}

	// If the exact tx (not a double spend) is already included but
	// unconfirmed, move it to a block.
	if r, ok := s.unconfirmed.txs[*tx.Sha()]; ok {
		r.Tx().SetIndex(tx.Index())
		if err := s.moveMinedTx(r, block); err != nil {
			return nil, err
		}
		return &TxRecord{key, r, s}, nil
	}

	// If this transaction is not already saved unconfirmed, remove all
	// unconfirmed transactions that are now invalidated due to being a
	// double spend.  This also handles killing unconfirmed transaction
	// spend chains if any other unconfirmed transactions spend outputs
	// of the removed double spend.
	if err := s.removeDoubleSpends(tx); err != nil {
		return nil, err
	}

	r := s.blockTxRecordForInserts(tx, block)
	if r.received.IsZero() {
		if !block.Time.IsZero() && block.Time.Before(received) {
			received = block.Time
		}
		r.received = received
	}
	return &TxRecord{key, r, s}, nil
}

// Received returns the earliest known time the transaction was received by.
func (t *TxRecord) Received() time.Time {
	return t.received
}

// Block returns the block details for a transaction.  If the transaction is
// unmined, both the block and returned error are nil.
func (t *TxRecord) Block() (*Block, error) {
	coll, err := t.s.lookupBlock(t.BlockHeight)
	if err != nil {
		if err == MissingBlockError(-1) {
			return nil, nil
		}
		return nil, err
	}
	return &coll.Block, nil
}

// AddDebits marks a transaction record as having debited from all them transaction
// credits in the spent slice.  If spent is nil, the previous debits will be found,
// however this is an expensive lookup and should be avoided if possible.
func (t *TxRecord) AddDebits(spent []*Credit) (*Debits, error) {
	if t.debits == nil {
		// Find now-spent credits if no debits have been previously set
		// and none were passed in by the caller.
		if len(spent) == 0 {
			foundSpent, err := t.s.findPreviousCredits(t.Tx())
			if err != nil {
				return nil, err
			}
			spent = foundSpent
		}

		debitAmount, err := t.s.markOutputsSpent(spent, t)
		if err != nil {
			return nil, err
		}
		t.debits = &debits{amount: debitAmount}
	}

	switch t.BlockHeight {
	case -1: // unconfimred
		for _, c := range spent {
			op := c.OutPoint()
			switch c.BlockHeight {
			case -1: // unconfirmed
				t.s.unconfirmed.spentUnconfirmed[*op] = t.txRecord
			default:
				key := c.outputKey()
				t.s.unconfirmed.spentBlockOutPointKeys[*op] = *key
				t.s.unconfirmed.spentBlockOutPoints[*key] = t.txRecord
			}
		}

	default:
		if t.debits.spends == nil {
			prevOutputKeys := make([]*BlockOutputKey, 0, len(spent))
			for _, c := range spent {
				prevOutputKeys = append(prevOutputKeys, c.outputKey())
			}
			err := t.txRecord.setDebitsSpends(prevOutputKeys, t.tx)
			if err != nil {
				if err == ErrDuplicateInsert {
					return &Debits{t}, nil
				}
				return nil, err
			}
		}
	}
	return &Debits{t}, nil
}

// findPreviousCredits searches for all unspent credits that make up the inputs
// for tx.  This lookup is very expensive and should be avoided at all costs.
func (s *Store) findPreviousCredits(tx *btcutil.Tx) ([]*Credit, error) {
	unfound := make(map[btcwire.OutPoint]struct{}, len(tx.MsgTx().TxIn))
	for _, txIn := range tx.MsgTx().TxIn {
		unfound[txIn.PreviousOutpoint] = struct{}{}
	}

	spent := make([]*Credit, 0, len(unfound))

done:
	for blockHeight := range s.unspent {
		b, err := s.lookupBlock(blockHeight)
		if err != nil {
			return nil, err
		}

		for blockIndex, txIdx := range b.unspent {
			if uint32(len(b.txs)) <= txIdx {
				return nil, MissingBlockTxError{
					BlockIndex:  blockIndex,
					BlockHeight: blockHeight,
				}
			}
			r := b.txs[txIdx]

			op := btcwire.OutPoint{Hash: *r.Tx().Sha()}
			for i, cred := range r.credits {
				if cred == nil || cred.spentBy != nil {
					continue
				}

				op.Index = uint32(i)
				if _, ok := unfound[op]; ok {
					key := BlockTxKey{blockIndex, b.Height}
					t := &TxRecord{key, r, s}
					c := &Credit{t, op.Index}
					spent = append(spent, c)

					delete(unfound, op)
					if len(unfound) == 0 {
						break done
					}
				}
			}
		}
	}

	return spent, nil
}

// markOutputsSpent marks each previous credit spent by t as spent.  The total
// input of all spent previous outputs is returned.
func (s *Store) markOutputsSpent(spent []*Credit, t *TxRecord) (btcutil.Amount, error) {
	var a btcutil.Amount
	for _, prev := range spent {
		switch prev.BlockHeight {
		case -1: // unconfirmed
			op := prev.OutPoint()
			s.unconfirmed.spentUnconfirmed[*op] = t.txRecord

		default:
			b, err := s.lookupBlock(prev.BlockHeight)
			if err != nil {
				return 0, err
			}
			r, _, err := b.lookupTxRecord(prev.BlockIndex)
			if err != nil {
				return 0, err
			}

			// Update spent info.  If this transaction (and possibly
			// block) no longer contains any unspent transactions,
			// remove from bookkeeping maps.
			credit := prev.txRecord.credits[prev.OutputIndex]
			if credit.spentBy != nil {
				if *credit.spentBy == t.BlockTxKey {
					continue
				}
				return 0, ErrInconsistentStore
			}
			credit.spentBy = &t.BlockTxKey
			if !r.hasUnspents() {
				delete(b.unspent, prev.BlockIndex)
				if len(b.unspent) == 0 {
					delete(s.unspent, b.Height)
				}
			}
			if t.BlockHeight == -1 { // unconfirmed
				op := prev.OutPoint()
				key := prev.outputKey()
				s.unconfirmed.spentBlockOutPointKeys[*op] = *key
				s.unconfirmed.spentBlockOutPoints[*key] = t.txRecord
			}

			// Increment total debited amount.
			v := r.Tx().MsgTx().TxOut[prev.OutputIndex].Value
			a += btcutil.Amount(v)
		}
	}

	// If t refers to a mined transaction, update its block's amount deltas
	// by the total debited amount.
	if t.BlockHeight != -1 {
		b, err := s.lookupBlock(t.BlockHeight)
		if err != nil {
			return 0, err
		}
		b.amountDeltas.Spendable -= a
	}

	return a, nil
}

func (r *txRecord) hasUnspents() bool {
	for _, credit := range r.credits {
		if credit == nil {
			continue
		}
		if credit.spentBy == nil {
			return true
		}
	}
	return false
}

// AddCredit marks the transaction record as containing a transaction output
// spendable by wallet.  The output is added unspent, and is marked spent
// when a new transaction spending the output is inserted into the store.
func (t *TxRecord) AddCredit(index uint32, change bool) (*Credit, error) {
	if len(t.tx.MsgTx().TxOut) <= int(index) {
		return nil, errors.New("transaction output does not exist")
	}

	c := &credit{change: change}
	if err := t.txRecord.setCredit(c, index, t.tx); err != nil {
		if err == ErrDuplicateInsert {
			return &Credit{t, index}, nil
		}
		return nil, err
	}

	switch t.BlockHeight {
	case -1: // unconfirmed
	default:
		b, err := t.s.lookupBlock(t.BlockHeight)
		if err != nil {
			return nil, err
		}
		_, txsIndex, err := b.lookupTxRecord(t.Tx().Index())
		if err != nil {
			return nil, err
		}

		// New outputs are added unspent.
		t.s.unspent[t.BlockTxKey.BlockHeight] = struct{}{}
		b.unspent[t.Tx().Index()] = txsIndex
		switch a := t.tx.MsgTx().TxOut[index].Value; t.tx.Index() {
		case 0: // Coinbase
			b.amountDeltas.Reward += btcutil.Amount(a)
		default:
			b.amountDeltas.Spendable += btcutil.Amount(a)
		}
	}

	return &Credit{t, index}, nil
}

// Rollback removes all blocks at height onwards, moving any transactions within
// each block to the unconfirmed pool.
func (s *Store) Rollback(height int32) error {
	i := len(s.blocks)
	for i != 0 && s.blocks[i-1].Height >= height {
		i--
	}
	detached := s.blocks[i:]
	s.blocks = s.blocks[:i]
	for _, b := range detached {
		delete(s.blockIndexes, b.Block.Height)
		delete(s.unspent, b.Block.Height)
		for _, r := range b.txs {
			oldTxIndex := r.Tx().Index()

			// If the removed transaction is a coinbase, do not move
			// it to unconfirmed.
			if oldTxIndex == 0 {
				continue
			}

			r.Tx().SetIndex(btcutil.TxIndexUnknown)
			s.unconfirmed.txs[*r.Tx().Sha()] = r
			for _, input := range r.Tx().MsgTx().TxIn {
				op := input.PreviousOutpoint
				s.unconfirmed.previousOutpoints[op] = r
			}

			// For each detached spent credit, lookup the spender
			// and modify its debit record to reference spending an
			// unconfirmed transaction.
			for outIdx, credit := range r.credits {
				if credit == nil {
					continue
				}
				spenderKey := credit.spentBy
				if spenderKey == nil {
					continue
				}

				prev := BlockOutputKey{
					BlockTxKey: BlockTxKey{
						BlockIndex:  oldTxIndex,
						BlockHeight: b.Height,
					},
					OutputIndex: uint32(outIdx),
				}

				// Lookup txRecord of the spending transaction.  Spent
				// tracking differs slightly depending on whether the
				// spender is confirmed or not.
				switch spenderKey.BlockHeight {
				case -1: // unconfirmed
					spender, ok := s.unconfirmed.spentBlockOutPoints[prev]
					if !ok {
						return ErrInconsistentStore
					}

					// Swap the maps the spender is saved in.
					op := btcwire.OutPoint{
						Hash:  *r.Tx().Sha(),
						Index: uint32(outIdx),
					}
					delete(s.unconfirmed.spentBlockOutPointKeys, op)
					delete(s.unconfirmed.spentBlockOutPoints, prev)
					s.unconfirmed.spentUnconfirmed[op] = spender

				default:
					spender, err := s.lookupBlockTx(*spenderKey)
					if err != nil {
						return err
					}

					if spender.debits == nil {
						return MissingDebitsError(*spenderKey)
					}

					current := BlockOutputKey{
						BlockTxKey: BlockTxKey{BlockHeight: -1},
					}
					err = spender.swapDebits(&prev, &current)
					if err != nil {
						return err
					}
				}

			}

			// If this transaction debits any previous credits,
			// modify each previous credit to mark it as spent
			// by an unconfirmed tx.
			if r.debits != nil {
				for _, prev := range r.debits.spends {
					rr, err := s.lookupBlockTx(prev.BlockTxKey)
					if err != nil {
						return err
					}
					c, err := rr.lookupBlockCredit(*prev)
					if err != nil {
						return err
					}
					op := btcwire.OutPoint{
						Hash:  *rr.Tx().Sha(),
						Index: uint32(prev.OutputIndex),
					}
					s.unconfirmed.spentBlockOutPointKeys[op] = *prev
					s.unconfirmed.spentBlockOutPoints[*prev] = r
					c.spentBy = &BlockTxKey{BlockHeight: -1}
				}

				// Debit tracking for unconfirmed transactions is
				// done by the unconfirmed store's maps, and not
				// in the txRecord itself.
				r.debits.spends = nil
			}
		}
	}
	return nil
}

func (r *txRecord) swapDebits(previous, current *BlockOutputKey) error {
	for i, outputKey := range r.debits.spends {
		if outputKey == nil {
			continue
		}
		if *outputKey == *previous {
			r.debits.spends[i] = current
			return nil
		}
	}

	return MissingCreditError(*previous)
}

// UnminedDebitTxs returns the underlying transactions for all wallet
// transactions which debit from previous outputs and are not known to have
// been mined in a block.
func (s *Store) UnminedDebitTxs() []*btcutil.Tx {
	unmined := make([]*btcutil.Tx, 0, len(s.unconfirmed.txs))
	for _, r := range s.unconfirmed.spentBlockOutPoints {
		unmined = append(unmined, r.Tx())
	}
	for _, r := range s.unconfirmed.spentUnconfirmed {
		unmined = append(unmined, r.Tx())
	}
	return unmined
}

// removeDoubleSpends checks for any unconfirmed transactions which would
// introduce a double spend if tx was added to the store (either as a confirmed
// or unconfirmed transaction).  If one is found, it and all transactions which
// spends its outputs (if any) are removed, and all previous inputs for any
// removed transactions are set to unspent.
func (s *Store) removeDoubleSpends(tx *btcutil.Tx) error {
	if ds := s.unconfirmed.findDoubleSpend(tx); ds != nil {
		return s.removeConflict(ds)
	}
	return nil
}

func (u *unconfirmedStore) findDoubleSpend(tx *btcutil.Tx) *txRecord {
	for _, input := range tx.MsgTx().TxIn {
		if r, ok := u.previousOutpoints[input.PreviousOutpoint]; ok {
			return r
		}
	}
	return nil
}

// removeConflict removes an unconfirmed transaction record and all spend chains
// deriving from it from the store.  This is designed to remove transactions
// that would otherwise result in double spend conflicts if left in the store.
// All not-removed credits spent by removed transactions are set unspent.
func (s *Store) removeConflict(r *txRecord) error {
	u := &s.unconfirmed

	// If this transaction contains any spent credits (which must be spent by
	// other unconfirmed transactions), recursively remove each spender.
	for i, credit := range r.credits {
		if credit == nil || credit.spentBy == nil {
			continue
		}
		op := btcwire.NewOutPoint(r.Tx().Sha(), uint32(i))
		nextSpender, ok := u.spentUnconfirmed[*op]
		if !ok {
			return ErrInconsistentStore
		}
		if err := s.removeConflict(nextSpender); err != nil {
			return err
		}
	}

	// If this tx spends any previous credits, set each unspent.
	for _, input := range r.Tx().MsgTx().TxIn {
		delete(u.previousOutpoints, input.PreviousOutpoint)

		// For all mined transactions with credits spent by this
		// conflicting transaction, remove from the bookkeeping maps
		// and set each previous record's credit as unspent.
		prevKey, ok := u.spentBlockOutPointKeys[input.PreviousOutpoint]
		if ok {
			delete(u.spentBlockOutPointKeys, input.PreviousOutpoint)
			delete(u.spentBlockOutPoints, prevKey)
			prev, err := s.lookupBlockTx(prevKey.BlockTxKey)
			if err != nil {
				return err
			}
			prev.credits[prevKey.OutputIndex].spentBy = nil
			continue
		}

		// For all unmined transactions with credits spent by this
		// conflicting transaction, remove from the unspent store's
		// spent tracking.
		//
		// Spend tracking is only handled by these maps, so there is
		// no need to modify the record and unset a spent-by pointer.
		if _, ok := u.spentUnconfirmed[input.PreviousOutpoint]; ok {
			delete(u.spentUnconfirmed, input.PreviousOutpoint)
		}
	}

	delete(u.txs, *r.Tx().Sha())
	for _, input := range r.Tx().MsgTx().TxIn {
		delete(u.previousOutpoints, input.PreviousOutpoint)
	}
	return nil
}

// UnspentOutputs returns all unspent received transaction outputs.
// The order is undefined.
func (s *Store) UnspentOutputs() ([]*Credit, error) {
	unspent := make([]*Credit, 0, len(s.unspent))
	for height := range s.unspent {
		b, err := s.lookupBlock(height)
		if err != nil {
			return nil, err
		}
		for blockIndex, index := range b.unspent {
			r := b.txs[index]
			for outputIndex, credit := range r.credits {
				if credit == nil || credit.spentBy != nil {
					continue
				}
				key := BlockTxKey{blockIndex, b.Height}
				txRecord := &TxRecord{key, r, s}
				c := &Credit{txRecord, uint32(outputIndex)}
				unspent = append(unspent, c)
			}
		}
	}
	for _, r := range s.unconfirmed.txs {
		for outputIndex, credit := range r.credits {
			if credit == nil || credit.spentBy != nil {
				continue
			}
			key := BlockTxKey{BlockHeight: -1}
			txRecord := &TxRecord{key, r, s}
			c := &Credit{txRecord, uint32(outputIndex)}
			unspent = append(unspent, c)
		}
	}
	return unspent, nil
}

// confirmed checks whether a transaction at height txHeight has met
// minconf confirmations for a blockchain at height curHeight.
func confirmed(minconf int, txHeight, curHeight int32) bool {
	return confirms(txHeight, curHeight) >= int32(minconf)
}

// confirms returns the number of confirmations for a transaction in a
// block at height txHeight (or -1 for an unconfirmed tx) given the chain
// height curHeight.
func confirms(txHeight, curHeight int32) int32 {
	switch {
	case txHeight == -1, txHeight > curHeight:
		return 0
	default:
		return curHeight - txHeight + 1
	}
}

// Balance returns the spendable wallet balance (total value of all unspent
// transaction outputs) given a minimum of minConf confirmations, calculated
// at a current chain height of curHeight.  Coinbase outputs are only included
// in the balance if maturity has been reached.
func (s *Store) Balance(minConf int, chainHeight int32) (btcutil.Amount, error) {
	var bal btcutil.Amount

	// Shadow these functions to avoid repeating arguments unnecesarily.
	confirms := func(height int32) int32 {
		return confirms(height, chainHeight)
	}
	confirmed := func(height int32) bool {
		return confirmed(minConf, height, chainHeight)
	}

	for _, b := range s.blocks {
		if confirmed(b.Height) {
			bal += b.amountDeltas.Spendable
			if confirms(b.Height) >= btcchain.CoinbaseMaturity {
				bal += b.amountDeltas.Reward
			}
			continue
		}
		// If there are still blocks that contain debiting transactions,
		// decrement the balance if they spend credits meeting minConf
		// confirmations.
		for _, r := range b.txs {
			if r.debits == nil {
				continue
			}
			for _, prev := range r.debits.spends {
				if !confirmed(prev.BlockHeight) {
					continue
				}
				r, err := s.lookupBlockTx(prev.BlockTxKey)
				if err != nil {
					return 0, err
				}
				v := r.Tx().MsgTx().TxOut[prev.OutputIndex].Value
				bal -= btcutil.Amount(v)
			}
		}
	}

	// Unconfirmed transactions which spend previous credits debit from
	// the returned balance, even with minConf > 0.
	for prev := range s.unconfirmed.spentBlockOutPoints {
		if confirmed(prev.BlockHeight) {
			r, err := s.lookupBlockTx(prev.BlockTxKey)
			if err != nil {
				return 0, err
			}
			v := r.Tx().MsgTx().TxOut[prev.OutputIndex].Value
			bal -= btcutil.Amount(v)
		}
	}

	// If unconfirmed credits are included, tally them as well.
	if minConf == 0 {
		for _, r := range s.unconfirmed.txs {
			for i, c := range r.credits {
				if c == nil {
					continue
				}
				if c.spentBy == nil {
					v := r.Tx().MsgTx().TxOut[i].Value
					bal += btcutil.Amount(v)
				}
			}
		}
	}

	return bal, nil
}

// Records returns a chronologically-ordered slice of all transaction records
// saved by the store.  This is sorted first by block height in increasing
// order, and then by transaction index for each tx in a block.
func (s *Store) Records() (records []*TxRecord) {
	for _, b := range s.blocks {
		for _, r := range b.txs {
			key := BlockTxKey{r.tx.Index(), b.Block.Height}
			records = append(records, &TxRecord{key, r, s})
		}
	}

	// Unconfirmed records are saved unsorted, and must be sorted by
	// received date on the fly.
	unconfirmed := make([]*TxRecord, len(s.unconfirmed.txs))
	for _, r := range s.unconfirmed.txs {
		key := BlockTxKey{BlockHeight: -1}
		unconfirmed = append(records, &TxRecord{key, r, s})
	}
	sort.Sort(byReceiveDate(unconfirmed))
	records = append(records, unconfirmed...)

	return
}

// Implementation of sort.Interface to sort transaction records by their
// receive date.
type byReceiveDate []*TxRecord

func (r byReceiveDate) Len() int           { return len(r) }
func (r byReceiveDate) Less(i, j int) bool { return r[i].received.Before(r[j].received) }
func (r byReceiveDate) Swap(i, j int)      { r[i], r[j] = r[j], r[i] }

// Debits returns the debit record for the transaction, or nil if the
// transaction does not debit from any previous transaction credits.
func (t *TxRecord) Debits() *Debits {
	if t.debits == nil {
		return nil
	}
	return &Debits{t}
}

// Credits returns all credit records for this transaction's outputs that are or
// were spendable by wallet.
func (t *TxRecord) Credits() []*Credit {
	credits := make([]*Credit, 0, len(t.credits))
	for i, c := range t.credits {
		if c != nil {
			credits = append(credits, &Credit{t, uint32(i)})
		}
	}
	return credits
}

// InputAmount returns the total amount debited from previous credits.
func (d *Debits) InputAmount() btcutil.Amount {
	return d.txRecord.debits.amount
}

// OutputAmount returns the total amount of all outputs for a transaction.
func (t *TxRecord) OutputAmount(ignoreChange bool) btcutil.Amount {
	a := btcutil.Amount(0)
	for i, txOut := range t.Tx().MsgTx().TxOut {
		if ignoreChange {
			switch cs := t.credits; {
			case i < len(cs) && cs[i] != nil && cs[i].change:
				continue
			}
		}
		a += btcutil.Amount(txOut.Value)
	}
	return a
}

// Fee returns the difference between the debited amount and the total
// transaction output.
func (d *Debits) Fee() btcutil.Amount {
	return d.InputAmount() - d.OutputAmount(false)
}

// Addresses parses the pubkey script, extracting all addresses for a
// standard script.
func (c *Credit) Addresses(net *btcnet.Params) (btcscript.ScriptClass,
	[]btcutil.Address, int, error) {

	msgTx := c.Tx().MsgTx()
	pkScript := msgTx.TxOut[c.OutputIndex].PkScript
	return btcscript.ExtractPkScriptAddrs(pkScript, net.Net)
}

// Change returns whether the credit is the result of a change output.
func (c *Credit) Change() bool {
	return c.txRecord.credits[c.OutputIndex].change
}

// Confirmed returns whether a transaction has reached some target number of
// confirmations, given the current best chain height.
func (t *TxRecord) Confirmed(target int, chainHeight int32) bool {
	return confirmed(target, t.BlockHeight, chainHeight)
}

// Confirmations returns the total number of confirmations a transaction has
// reached, given the current best chain height.
func (t *TxRecord) Confirmations(chainHeight int32) int32 {
	return confirms(t.BlockHeight, chainHeight)
}

// IsCoinbase returns whether the transaction is a coinbase.
func (t *TxRecord) IsCoinbase() bool {
	return t.BlockHeight != -1 && t.BlockIndex == 0
}

// Amount returns the amount credited to the account from a transaction output.
func (c *Credit) Amount() btcutil.Amount {
	msgTx := c.Tx().MsgTx()
	return btcutil.Amount(msgTx.TxOut[c.OutputIndex].Value)
}

// OutPoint returns the outpoint needed to include in a transaction input
// to spend this output.
func (c *Credit) OutPoint() *btcwire.OutPoint {
	return btcwire.NewOutPoint(c.Tx().Sha(), c.OutputIndex)
}

// outputKey creates and returns the block lookup key for this credit.
func (c *Credit) outputKey() *BlockOutputKey {
	return &BlockOutputKey{
		BlockTxKey:  c.BlockTxKey,
		OutputIndex: c.OutputIndex,
	}
}

// Spent returns whether the transaction output is currently spent or not.
func (c *Credit) Spent() bool {
	return c.txRecord.credits[c.OutputIndex].spentBy != nil
}

// TxOut returns the transaction output which this credit references.
func (c *Credit) TxOut() *btcwire.TxOut {
	return c.Tx().MsgTx().TxOut[c.OutputIndex]
}

// Tx returns the underlying transaction.
func (r *txRecord) Tx() *btcutil.Tx {
	return r.tx
}