From 603f3c70db3d83943ccdef4aac63200c26e4daa5 Mon Sep 17 00:00:00 2001
From: Chi Thanh NGUYEN <chithanhnguyen.math@gmail.com>
Date: Mon, 25 Jan 2021 14:50:41 +0000
Subject: [PATCH] add method allowing a transaction to add inputs knowing the
 previous utxos owner

---
 tx.go      | 24 ++++++++++++++++++++++++
 tx_test.go | 22 ++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/tx.go b/tx.go
index 0e254dca..98936476 100644
--- a/tx.go
+++ b/tx.go
@@ -1,6 +1,7 @@
 package bt
 
 import (
+	"bytes"
 	"encoding/binary"
 	"encoding/hex"
 	"errors"
@@ -132,6 +133,29 @@ func (tx *Tx) AddInput(input *Input) {
 	tx.Inputs = append(tx.Inputs, input)
 }
 
+// AddInputFromTx take all outputs from previous transaction
+// that match a specific public key, add it as input to this new transaction.
+func (tx *Tx) AddInputFromTx(pvsTx *Tx, matchPK []byte) error {
+	matchPKHASH160 := crypto.Hash160(matchPK)
+	for i, utxo := range pvsTx.Outputs {
+		utxoPkHASH160, errPK := utxo.LockingScript.GetPublicKeyHash()
+		if errPK != nil {
+			return errPK
+		}
+		if !bytes.Equal(utxoPkHASH160, matchPKHASH160) {
+			continue
+		}
+		tx.AddInput(&Input{
+			PreviousTxID:       pvsTx.GetTxID(),
+			PreviousTxOutIndex: uint32(i),
+			PreviousTxSatoshis: utxo.Satoshis,
+			PreviousTxScript:   utxo.LockingScript,
+			SequenceNumber:     0xffffffff,
+		})
+	}
+	return nil
+}
+
 // From adds a new input to the transaction from the specified UTXO fields.
 func (tx *Tx) From(txID string, vout uint32, prevTxLockingScript string, satoshis uint64) error {
 	pts, err := bscript.NewFromHexString(prevTxLockingScript)
diff --git a/tx_test.go b/tx_test.go
index f7c86cbd..3809ac47 100644
--- a/tx_test.go
+++ b/tx_test.go
@@ -113,6 +113,28 @@ func TestNewTxFromBytes(t *testing.T) {
 	})
 }
 
+func TestAddInputFromTx(t *testing.T) {
+	pubkey1 := []byte{1, 2, 3} // utxo test owner
+	pubkey2 := []byte{1, 2, 4}
+
+	output1, err1 := bt.NewP2PKHOutputFromPubKeyBytes(pubkey1, uint64(100000))
+	assert.NoError(t, err1)
+	output2, err2 := bt.NewP2PKHOutputFromPubKeyBytes(pubkey1, uint64(100000))
+	assert.NoError(t, err2)
+	output3, err3 := bt.NewP2PKHOutputFromPubKeyBytes(pubkey2, uint64(5000000))
+	assert.NoError(t, err3)
+
+	prvTx := bt.NewTx()
+	prvTx.AddOutput(output1)
+	prvTx.AddOutput(output2)
+	prvTx.AddOutput(output3)
+	newTx := bt.NewTx()
+	err := newTx.AddInputFromTx(prvTx, pubkey1)
+	assert.NoError(t, err)
+	assert.Equal(t, newTx.InputCount(), 2) // only 2 utxos has been added
+	assert.Equal(t, newTx.GetTotalInputSatoshis(), uint64(200000))
+}
+
 func TestTx_GetTxID(t *testing.T) {
 	t.Parallel()