transaction.go

package main

import (
	"bytes"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/sha256"
	"encoding/gob"
	"encoding/hex"
	"errors"
	"fmt"
	"log"
	"math/big"
	"strings"
)

const subsidy = 10

type Transaction struct {
	ID   []byte
	Vin  []TXInput
	Vout []TXOutput
}

func (tx *Transaction) SetID() {
	var encoded bytes.Buffer
	var hash [32]byte

	enc := gob.NewEncoder(&encoded)
	err := enc.Encode(tx)
	if err != nil {
		log.Panic(err)
	}
	hash = sha256.Sum256(encoded.Bytes())
	tx.ID = hash[:]
}

type TXInput struct {
	Txid      []byte
	Vout      int
	Signature []byte
	PubKey    []byte
}

type TXOutput struct {
	Value      int
	PubKeyHash []byte
}

func (tx Transaction) IsCoinbase() bool {
	return len(tx.Vin) == 1 && len(tx.Vin[0].Txid) == 0 && tx.Vin[0].Vout == -1
}

func (tx Transaction) Serialize() []byte {
	var encoded bytes.Buffer

	enc := gob.NewEncoder(&encoded)
	err := enc.Encode(tx)
	if err != nil {
		log.Panic(err)
	}

	return encoded.Bytes()
}

func (tx *Transaction) Hash() []byte {
	var hash [32]byte

	txCopy := *tx
	txCopy.ID = []byte{}

	hash = sha256.Sum256(txCopy.Serialize())

	return hash[:]
}

func (in *TXInput) UsesKey(pubKeyHash []byte) bool {
	lockingHash := HashPubKey(in.PubKey)

	return bytes.Compare(lockingHash, pubKeyHash) == 0
}

func (out *TXOutput) Lock(address []byte) {
	pubKeyHash := Base58Decode(address)
	pubKeyHash = pubKeyHash[1 : len(pubKeyHash)-4]
	out.PubKeyHash = pubKeyHash
}

func (out *TXOutput) IsLockedWithKey(pubKeyHash []byte) bool {
	return bytes.Compare(out.PubKeyHash, pubKeyHash) == 0
}

func NewTXOutput(value int, address string) *TXOutput {
	txo := &TXOutput{value, nil}
	txo.Lock([]byte(address))

	return txo
}

func (tx *Transaction) Sign(privKey ecdsa.PrivateKey, prevTXs map[string]Transaction) {
	if tx.IsCoinbase() {
		return
	}

	txCopy := tx.TrimmedCopy()

	/*
		Code for add signature to TX
	*/
	for inID, vin := range txCopy.Vin {
		prevTx := prevTXs[hex.EncodeToString(vin.Txid)]
		txCopy.Vin[inID].Signature = nil
		txCopy.Vin[inID].PubKey = prevTx.Vout[vin.Vout].PubKeyHash
		txCopy.ID = txCopy.Hash()
		txCopy.Vin[inID].PubKey = nil

		r, s, err := ecdsa.Sign(rand.Reader, &privKey, txCopy.ID)
		if err != nil {
			log.Panic(err)
		}

		signature := append(r.Bytes(), s.Bytes()...)

		tx.Vin[inID].Signature = signature
	}
}

func (tx Transaction) String() string {
	var lines []string

	lines = append(lines, fmt.Sprintf("--- Transaction %x:", tx.ID))

	for i, input := range tx.Vin {

		lines = append(lines, fmt.Sprintf("     Input %d:", i))
		lines = append(lines, fmt.Sprintf("       TXID:      %x", input.Txid))
		lines = append(lines, fmt.Sprintf("       Out:       %d", input.Vout))
		lines = append(lines, fmt.Sprintf("       Signature: %x", input.Signature))
		lines = append(lines, fmt.Sprintf("       PubKey:    %x", input.PubKey))
	}

	for i, output := range tx.Vout {
		lines = append(lines, fmt.Sprintf("     Output %d:", i))
		lines = append(lines, fmt.Sprintf("       Value:  %d", output.Value))
		lines = append(lines, fmt.Sprintf("       Script: %x", output.PubKeyHash))
	}

	return strings.Join(lines, "\n")
}

func (tx *Transaction) TrimmedCopy() Transaction {
	var inputs []TXInput
	var outputs []TXOutput

	for _, vin := range tx.Vin {
		inputs = append(inputs, TXInput{vin.Txid, vin.Vout, nil, nil})
	}

	for _, vout := range tx.Vout {
		outputs = append(outputs, TXOutput{vout.Value, vout.PubKeyHash})
	}

	txCopy := Transaction{tx.ID, inputs, outputs}

	return txCopy
}

func (tx *Transaction) Verify(prevTXs map[string]Transaction) bool {
	txCopy := tx.TrimmedCopy()
	curve := elliptic.P256()

	for inID, vin := range tx.Vin {
		prevTx := prevTXs[hex.EncodeToString(vin.Txid)]
		txCopy.Vin[inID].Signature = nil
		txCopy.Vin[inID].PubKey = prevTx.Vout[vin.Vout].PubKeyHash
		txCopy.ID = txCopy.Hash()
		txCopy.Vin[inID].PubKey = nil

		r := big.Int{}
		s := big.Int{}
		sigLen := len(vin.Signature)
		r.SetBytes(vin.Signature[:(sigLen / 2)])
		s.SetBytes(vin.Signature[(sigLen / 2):])

		x := big.Int{}
		y := big.Int{}
		keyLen := len(vin.PubKey)
		x.SetBytes(vin.PubKey[:(keyLen / 2)])
		y.SetBytes(vin.PubKey[(keyLen / 2):])

		rawPubKey := ecdsa.PublicKey{curve, &x, &y}
		if ecdsa.Verify(&rawPubKey, txCopy.ID, &r, &s) == false {
			return false
		}
	}

	return true
}

func (bc *Blockchain) FindTransaction(ID []byte) (Transaction, error) {
	bci := bc.Iterator()

	for {
		block := bci.Next()

		for _, tx := range block.Transactions {
			if bytes.Compare(tx.ID, ID) == 0 {
				return *tx, nil
			}
		}

		if len(block.PrevBlockHash) == 0 {
			break
		}
	}

	return Transaction{}, errors.New("Transaction is not found")
}

func (bc *Blockchain) SignTransaction(tx *Transaction, privKey ecdsa.PrivateKey) {
	prevTXs := make(map[string]Transaction)

	for _, vin := range tx.Vin {
		prevTX, _ := bc.FindTransaction(vin.Txid)
		prevTXs[hex.EncodeToString(prevTX.ID)] = prevTX
	}

	tx.Sign(privKey, prevTXs)
}

func (bc *Blockchain) VerifyTransaction(tx *Transaction) bool {
	prevTXs := make(map[string]Transaction)

	for _, vin := range tx.Vin {
		prevTX, _ := bc.FindTransaction(vin.Txid)
		prevTXs[hex.EncodeToString(prevTX.ID)] = prevTX
	}

	return tx.Verify(prevTXs)
}

//func (in *TXInput) CanUnlockOutputWith(unlockingData string) bool {
//	return in.ScriptSig == unlockingData
//}
//
//func (out *TXOutput) CanBeUnlockedWith(unlockingData string) bool {
//	return out.ScriptPubKey == unlockingData
//}

func NewCoinbaseTX(to, data string) *Transaction {
	if data == "" {
		data = fmt.Sprintf("Reward to '%s'", to)
	}

	txin := TXInput{[]byte{}, -1, nil, []byte(data)}
	txout := NewTXOutput(subsidy, to)
	tx := Transaction{nil, []TXInput{txin}, []TXOutput{*txout}}
	tx.ID = tx.Hash()

	return &tx
}

//func NewUTXOTransaction(from, to string, amount int, bc *Blockchain) *Transaction {
//	var inputs []TXInput
//	var outputs []TXOutput
//
//	acc, validOutputs := bc.FindSpendableOutputs(from, amount)
//
//	if acc < amount {
//		log.Panic("ERROR: Not enough funds")
//	}
//
//	for txid, outs := range validOutputs {
//		txID, err := hex.DecodeString(txid)
//		if err != nil {
//			log.Panic(err)
//		}
//
//		for _, out := range outs {
//			input := TXInput{txID, out, from}
//			inputs = append(inputs, input)
//		}
//	}
//
//	outputs = append(outputs, TXOutput{amount, to})
//	if acc > amount {
//		outputs = append(outputs, TXOutput{acc - amount, from}) // a change
//	}
//
//	tx := Transaction{nil, inputs, outputs}
//	tx.SetID()
//
//	return &tx
//}

func NewUTXOTransaction(from, to string, amount int, bc *Blockchain) *Transaction {
	var inputs []TXInput
	var outputs []TXOutput

	wallets, err := NewWallets()
	if err != nil {
		log.Panic(err)
	}
	wallet := wallets.GetWallet(from)
	pubKeyHash := HashPubKey(wallet.PublicKey)
	acc, validOutputs := bc.FindSpendableOutputs(pubKeyHash, amount)

	if acc < amount {
		log.Panic("ERROR: Not enough funds")
	}

	// Build a list of inputs
	for txid, outs := range validOutputs {
		txID, err := hex.DecodeString(txid)
		if err != nil {
			log.Panic(err)
		}

		for _, out := range outs {
			input := TXInput{txID, out, nil, wallet.PublicKey}
			inputs = append(inputs, input)
		}
	}

	// Build a list of outputs
	outputs = append(outputs, *NewTXOutput(amount, to))
	if acc > amount {
		outputs = append(outputs, *NewTXOutput(acc-amount, from)) // a change
	}

	tx := Transaction{nil, inputs, outputs}
	tx.ID = tx.Hash()
	bc.SignTransaction(&tx, wallet.PrivateKey)

	return &tx
}