From c358fc754d0548b96892987a32739c4f76157662 Mon Sep 17 00:00:00 2001
From: Minh Doan <minh@simple-rules.com>
Date: Fri, 15 Jun 2018 22:53:14 -0700
Subject: [PATCH] add data structure for UTXOPool and update verify_new_block

---
 blockchain/blockchain.go      | 30 +++++++++++++++++++++++++-----
 blockchain/blockchain_test.go |  2 +-
 blockchain/transaction.go     |  2 +-
 blockchain/utxopool.go        |  8 ++++++++
 4 files changed, 35 insertions(+), 7 deletions(-)
 create mode 100644 blockchain/utxopool.go

diff --git a/blockchain/blockchain.go b/blockchain/blockchain.go
index edcab3389..00b247f46 100644
--- a/blockchain/blockchain.go
+++ b/blockchain/blockchain.go
@@ -3,7 +3,6 @@ package blockchain
 import (
 	"bytes"
 	"encoding/hex"
-	"fmt"
 )
 
 // Blockchain keeps a sequence of Blocks
@@ -144,17 +143,38 @@ func (bc *Blockchain) AddNewTransferAmount(from, to string, amount int) *Blockch
 }
 
 // VerifyNewBlock verifies if the new coming block is valid for the current blockchain.
-func (bc *Blockchain) VerifyNewBlock(block *Block) bool {
+func (bc *Blockchain) VerifyNewBlock(utxopool *UTXOPool, block *Block) bool {
 	length := len(bc.blocks)
 	if bytes.Compare(block.PrevBlockHash, bc.blocks[length-1].Hash) != 0 {
-		fmt.Println("MINh1")
 		return false
 	}
 	if block.Timestamp < bc.blocks[length-1].Timestamp {
-		fmt.Println("MINh2")
 		return false
 	}
-	// TODO(minhdoan): Check Transactions parts
+
+	if utxopool != nil {
+		for _, tx := range block.Transactions {
+			inTotal := 0
+			// Calculate the sum of TxInput
+			for _, in := range tx.TxInput {
+				inTxID := hex.EncodeToString(in.TxID)
+				if val, ok := utxopool.utxo[in.Address][inTxID]; ok {
+					inTotal += val
+				} else {
+					return false
+				}
+			}
+
+			outTotal := 0
+			// Calculate the sum of TxOutput
+			for _, out := range tx.TxOutput {
+				outTotal += out.Value
+			}
+			if inTotal != outTotal {
+				return false
+			}
+		}
+	}
 	return true
 }
 
diff --git a/blockchain/blockchain_test.go b/blockchain/blockchain_test.go
index 0fb2003c9..f10d4fba3 100644
--- a/blockchain/blockchain_test.go
+++ b/blockchain/blockchain_test.go
@@ -73,7 +73,7 @@ func TestVerifyNewBlock(t *testing.T) {
 	}
 	newBlock := NewBlock([]*Transaction{tx}, bc.blocks[len(bc.blocks)-1].Hash)
 
-	if !bc.VerifyNewBlock(newBlock) {
+	if !bc.VerifyNewBlock(nil, newBlock) {
 		t.Error("failed to add a new valid block.")
 	}
 }
diff --git a/blockchain/transaction.go b/blockchain/transaction.go
index ea96d595e..2ccf34a63 100644
--- a/blockchain/transaction.go
+++ b/blockchain/transaction.go
@@ -11,7 +11,7 @@ import (
 
 // Transaction represents a Bitcoin transaction
 type Transaction struct {
-	ID       []byte         // 32 byte hash
+	ID       []byte // 32 byte hash
 	TxInput  []TXInput
 	TxOutput []TXOutput
 }
diff --git a/blockchain/utxopool.go b/blockchain/utxopool.go
new file mode 100644
index 000000000..0a7a13558
--- /dev/null
+++ b/blockchain/utxopool.go
@@ -0,0 +1,8 @@
+package blockchain
+
+// UTXOPool stores transactions and balance associated with each address.
+type UTXOPool struct {
+	// Mapping from address to a map of transaction id to that balance.
+	// The assumption here is that one address only appears once output array in a transaction.
+	utxo map[string]map[string]int
+}