From 31472956d5bc80508bfd5ebecc2fa552bb69104d Mon Sep 17 00:00:00 2001
From: Minh Doan <minh@simple-rules.com>
Date: Mon, 18 Jun 2018 21:22:53 -0700
Subject: [PATCH] add verification/selection a set of valid transactions

---
 blockchain/utxopool.go | 90 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)

diff --git a/blockchain/utxopool.go b/blockchain/utxopool.go
index cb198c054..e79e88f62 100644
--- a/blockchain/utxopool.go
+++ b/blockchain/utxopool.go
@@ -4,6 +4,10 @@ import (
 	"encoding/hex"
 )
 
+const (
+	MaxNumberOfTransactions = 100
+)
+
 // UTXOPool stores transactions and balance associated with each address.
 type UTXOPool struct {
 	// Mapping from address to a map of transaction id to a map of the index of output
@@ -57,6 +61,80 @@ func (utxopool *UTXOPool) VerifyTransactions(transactions []*Transaction) bool {
 	return true
 }
 
+// VerifyOneTransactionAndUpdate verifies if a list of transactions valid.
+func (utxopool *UTXOPool) VerifyOneTransaction(tx *Transaction) bool {
+    spentTXOs := make(map[string]map[string]map[int]bool)
+    txID := hex.EncodeToString(tx.ID)
+    inTotal := 0
+    // Calculate the sum of TxInput
+    for _, in := range tx.TxInput {
+        inTxID := hex.EncodeToString(in.TxID)
+        index := in.TxOutputIndex
+        // Check if the transaction with the addres is spent or not.
+        if val, ok := utxopool.utxo[in.Address][inTxID][index]; ok {
+            if spentTXOs[in.Address][inTxID][index] {
+                return false
+            }
+            inTotal += val
+        } else {
+            return false
+        }
+        // Mark the transactions with the address and index spent.
+        if _, ok := spentTXOs[in.Address]; !ok {
+            spentTXOs[in.Address] = make(map[string]map[int]bool)
+        }
+        if _, ok := spentTXOs[in.Address][inTxID]; !ok {
+            spentTXOs[in.Address][inTxID] = make(map[int]bool)
+        }
+        spentTXOs[in.Address][inTxID][index] = true
+    }
+
+    outTotal := 0
+    // Calculate the sum of TxOutput
+    for index, out := range tx.TxOutput {
+        if val, ok := spentTXOs[out.Address][txID][index]; ok {
+            return false
+        }
+        outTotal += out.Value
+    }
+    if inTotal != outTotal {
+        return false
+    }
+	return true
+}
+
+func (utxopool *UTXOPool) Update(tx* Transaction) {
+	if utxopool != nil {
+        txID := hex.EncodeToString(tx.ID)
+
+        // Remove
+        for _, in := range tx.TxInput {
+            inTxID := hex.EncodeToString(in.TxID)
+            delete(utxopool.utxo[in.Address][inTxID], in.TxOutputIndex)
+        }
+
+        // Update
+        for index, out := range tx.TxOutput {
+            if _, ok := utxopool.utxo[out.Address]; !ok {
+                utxopool.utxo[out.Address] = make(map[string]map[int]int)
+                utxopool.utxo[out.Address][txID] = make(map[int]int)
+            }
+            if _, ok := utxopool.utxo[out.Address][txID]; !ok {
+                utxopool.utxo[out.Address][txID] = make(map[int]int)
+            }
+            utxopool.utxo[out.Address][txID][index] = out.Value
+        }
+    }
+}
+
+func (utxopool *UTXOPool) VerifyOneTransactionAndUpdate(tx *Transaction) bool {
+    if utxopool.VerifyOneTransaction(tx) {
+        utxopool.Update(tx)
+        return true
+    }
+    retur false
+}
+
 // VerifyAndUpdate verifies a list of transactions and update utxoPool.
 func (utxopool *UTXOPool) VerifyAndUpdate(transactions []*Transaction) bool {
 	if utxopool.VerifyTransactions(transactions) {
@@ -111,3 +189,15 @@ func CreateUTXOPoolFromGenesisBlockChain(bc *Blockchain) *UTXOPool {
 	tx := bc.blocks[0].Transactions[0]
 	return CreateUTXOPoolFromTransaction(tx)
 }
+
+// SelectTransactionsForNewBlock returns a list of index of valid transactions for the new block.
+func (utxoPool *UTXOPool) SelectTransactionsForNewBlock(transactions []*Transaction) (selected, unselected []*Transaction) {
+	selected, unselected = []*Transaction{}, []*Transaction{}
+	for id, tx := range transactions {
+        if len(selected) < MaxNumberOfTransactions && utxoPool.VerifyOneTransactionAndUpdate(tx) {
+            append(selected, tx)
+        } else {
+            append(unselected, tx)
+        }
+	}
+}