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‎.gitignore

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HELP.md
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target/
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!.mvn/wrapper/maven-wrapper.jar
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!**/src/main/**
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!**/src/test/**
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### IntelliJ IDEA ###
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.idea
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*.iws
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*.iml
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*.ipr
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‎pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.pavlmits</groupId>
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<artifactId>blockchain-chat</artifactId>
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<version>1.0-SNAPSHOT</version>
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<dependencies>
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-lang3</artifactId>
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<version>3.9</version>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-compiler-plugin</artifactId>
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<configuration>
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<source>11</source>
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<target>11</target>
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</configuration>
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</plugin>
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</plugins>
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</build>
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</project>

‎src/main/java/com/pavlmits/blockchain/chat/Block.java

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package com.pavlmits.blockchain.chat;
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import java.util.ArrayList;
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import java.util.Date;
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import java.util.List;
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import java.util.Random;
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public class Block {
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private final int id;
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private final int magicNumber;
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private final int padding;
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private final long timestamp;
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private final String miner;
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private final String currentHash;
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private final String previousHash;
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private final List<String> messages;
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Block(int id, int magicNumber, String previousHash, int padding, long timestamp, String hash, String miner, List<String> messages) {
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this.id = id;
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this.magicNumber = magicNumber;
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this.previousHash = previousHash;
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this.padding = padding;
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this.timestamp = timestamp;
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this.currentHash = hash;
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this.miner = miner;
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this.messages = new ArrayList<>(messages);
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}
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int getId() {
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return id;
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}
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String getCurrentHash() {
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return currentHash;
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}
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String getPreviousHash() {
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return previousHash;
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}
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long getTimestamp() {
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return timestamp;
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}
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int getMagicNumber() {
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return magicNumber;
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}
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public String getMiner() {
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return miner;
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}
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public int getPadding() {
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return padding;
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}
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public List<String> getMessages() {
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return messages;
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}
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}

‎src/main/java/com/pavlmits/blockchain/chat/Blockchain.java

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package com.pavlmits.blockchain.chat;
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import java.util.ArrayList;
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import java.util.List;
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public class Blockchain {
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private volatile int lastIdOfABlock;
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private volatile int padding;
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private volatile List<Block> blocks;
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private volatile long previousTimer;
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private volatile List<String> messages;
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Blockchain() {
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this.lastIdOfABlock = 1;
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this.padding = 1;
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this.previousTimer = 0;
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blocks = new ArrayList<>();
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messages = new ArrayList<>();
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}
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public boolean isValid() {
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for (int i = 0; i < blocks.size() - 1; i++) {
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if (!blocks.get(i + 1).getPreviousHash().equals(blocks.get(i).getCurrentHash()))
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return false;
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}
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return true;
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}
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void printAll() {
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for (Block block : blocks) {
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print(block);
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}
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}
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private void print(Block block) {
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System.out.println("Block: ");
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System.out.println("Created by miner #" + block.getMiner());
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System.out.println(block.getMiner() + "gets 100 VC");
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System.out.println("Id: " + block.getId());
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System.out.println("Timestamp: " + block.getTimestamp());
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System.out.println("Magic number: " + block.getMagicNumber());
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System.out.println("Hash of the previous block: \n" + block.getPreviousHash());
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System.out.println("Hash of the block: \n" + block.getCurrentHash());
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if (block.getMessages().isEmpty())
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System.out.println("Block data: no messages");
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else {
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System.out.println("Block data:");
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for (String message : block.getMessages()) {
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System.out.println(message);
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}
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}
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System.out.println("N was increased to " + block.getPadding());
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System.out.println();
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}
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public synchronized int getIdOfAnewBlock() {
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return lastIdOfABlock++;
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}
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public int getLastIdOfABlock() {
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return lastIdOfABlock;
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}
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public synchronized String getLastBlocksHash() {
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if (blocks.isEmpty())
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return "0";
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return blocks.get(blocks.size() - 1).getCurrentHash();
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}
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public synchronized void addBlock(String hash, int magicNumber, String minerName, long time) {
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Block block = new Block(getIdOfAnewBlock(), magicNumber, getLastBlocksHash(), padding, time, hash, minerName, messages);
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blocks.add(block);
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calculatePadding(time);
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}
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//TODO find effective way to calculate padding
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private synchronized void calculatePadding(long time) {
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if (time <= previousTimer && padding < 5) {
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previousTimer = time;
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padding++;
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messages.clear();
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} else {
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previousTimer = time;
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padding--;
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}
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}
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public int getPadding() {
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return padding;
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}
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public List<String> getMessages() {
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return messages;
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}
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}

‎src/main/java/com/pavlmits/blockchain/chat/Main.java

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package com.pavlmits.blockchain.chat;
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import java.util.ArrayList;
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import java.util.List;
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public class Main {
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public static void main(String[] args) throws InterruptedException {
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final Blockchain blockchain = new Blockchain();
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Miner miner = new Miner(blockchain);
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List<Thread> threads = new ArrayList<>();
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for (int i = 0; i < 5; i++) {
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Thread thread = new Thread(miner, String.valueOf(i));
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thread.start();
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threads.add(thread);
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}
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//TODO create real chat
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for (int i = 0; i < 10 ; i++) {
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blockchain.getMessages().add("-Message" + i);
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Thread.sleep(10);
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}
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boolean allDead=false;
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while(! allDead){
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allDead=true;
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for (Thread thread : threads)
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if (thread.isAlive()) allDead = false;
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Thread.sleep(2000);
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}
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blockchain.printAll();
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System.out.println(blockchain.isValid());
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//TODO add stage 5
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}
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}

‎src/main/java/com/pavlmits/blockchain/chat/Miner.java

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package com.pavlmits.blockchain.chat;
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import com.pavlmits.blockchain.chat.util.StringUtil;
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import org.apache.commons.lang3.tuple.ImmutablePair;
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import org.apache.commons.lang3.tuple.Pair;
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import java.util.Date;
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import java.util.Random;
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public class Miner implements Runnable {
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private Blockchain blockchain;
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public Miner(Blockchain blockchain) {
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this.blockchain = blockchain;
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}
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@Override
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public void run() {
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long startTime = System.nanoTime();
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Pair<Integer, String> pair = mine();
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long endTime = System.nanoTime();
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blockchain.addBlock(pair.getRight(), pair.getLeft(), Thread.currentThread().getName(),(endTime - startTime) / 1_000_000_000);
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}
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private synchronized Pair<Integer,String> mine() {
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return calculateHash(blockchain.getLastBlocksHash());
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}
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private Pair<Integer,String> calculateHash(String previousHash){
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int magicNumber = new Random().nextInt(Integer.MAX_VALUE);
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String hash = calculateSHA(blockchain.getLastIdOfABlock() + 1, previousHash, magicNumber);
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while (!hash.startsWith("0".repeat(blockchain.getPadding()))) {
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magicNumber = new Random().nextInt(Integer.MAX_VALUE);
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hash = calculateSHA(blockchain.getLastIdOfABlock() + 1, previousHash, magicNumber);
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}
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return ImmutablePair.of(magicNumber, hash);
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}
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private String calculateSHA(int id, String previousHash,int magicNumber) {
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String input = id + previousHash + new Date().getTime() + magicNumber;
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return StringUtil.applySha256(input);
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}
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}

‎src/main/java/com/pavlmits/blockchain/chat/util/BlockchainUtil.java

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package com.pavlmits.blockchain.chat.util;
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public class BlockchainUtil {
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//TODO
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public void importBlockchain(){ }
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public void exportBlockchain(){}
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}

‎src/main/java/com/pavlmits/blockchain/chat/util/StringUtil.java

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package com.pavlmits.blockchain.chat.util;
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import java.nio.charset.StandardCharsets;
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import java.security.MessageDigest;
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public class StringUtil {
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public static String applySha256(String input){
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try {
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MessageDigest digest = MessageDigest.getInstance("SHA-256");
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/* Applies sha256 to our input */
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byte[] hash = digest.digest(input.getBytes(StandardCharsets.UTF_8));
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StringBuilder hexString = new StringBuilder();
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for (byte elem: hash) {
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String hex = Integer.toHexString(0xff & elem);
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if(hex.length() == 1) hexString.append('0');
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hexString.append(hex);
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}
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return hexString.toString();
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}
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catch(Exception e) {
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throw new RuntimeException(e);
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}
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}
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}

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