Part six

src/blockchain/Block.java

@@ -0,0 +1,59 @@
+package blockchain;
+
+import blockchain.data.SignedData;
+import java.io.Serializable;
+import java.util.List;
+
+public class Block<T extends SignedData & Serializable> implements Serializable {
+
+  private final Integer id;
+  private final Long minerId;
+  private final String hashPreviousBlock;
+  private final String hash;
+  private final Long timestamp;
+  private final Integer magicNumber;
+  private List<T> data = List.of();
+
+
+  public Block(Integer id, Long minerId, String hashPreviousBlock, String hash,
+      Long timestamp, Integer magicNumber) {
+    this.id = id;
+    this.minerId = minerId;
+    this.hashPreviousBlock = hashPreviousBlock;
+    this.hash = hash;
+    this.timestamp = timestamp;
+    this.magicNumber = magicNumber;
+  }
+
+  public Integer getId() {
+    return id;
+  }
+
+  public String getHashPreviousBlock() {
+    return hashPreviousBlock;
+  }
+
+  public String getHash() {
+    return hash;
+  }
+
+  public Long getTimestamp() {
+    return timestamp;
+  }
+
+  public Integer getMagicNumber() {
+    return magicNumber;
+  }
+
+  public Long getMinerId() {
+    return minerId;
+  }
+
+  public List<T> getData() {
+    return data;
+  }
+
+  public void setData(List<T> data) {
+    this.data = data;
+  }
+}

src/blockchain/BlockBuilder.java

@@ -0,0 +1,48 @@
+package blockchain;
+
+import blockchain.data.SignedData;
+import java.io.Serializable;
+
+public class BlockBuilder<T extends SignedData & Serializable> {
+
+  private Integer id;
+  private Long minerId;
+  private String hashPreviousBlock;
+  private String hash;
+  private Long timestamp;
+  private Integer magicNumber;
+
+  public BlockBuilder<T> withId(Integer id) {
+    this.id = id;
+    return this;
+  }
+
+  public BlockBuilder<T> withMinerId(Long minerId) {
+    this.minerId = minerId;
+    return this;
+  }
+
+  public BlockBuilder<T> withHashPreviousBlock(String hashPreviousBlock) {
+    this.hashPreviousBlock = hashPreviousBlock;
+    return this;
+  }
+
+  public BlockBuilder<T> withHash(String hash) {
+    this.hash = hash;
+    return this;
+  }
+
+  public BlockBuilder<T> withTimestamp(Long timestamp) {
+    this.timestamp = timestamp;
+    return this;
+  }
+
+  public BlockBuilder<T> withMagicNumber(Integer magicNumber) {
+    this.magicNumber = magicNumber;
+    return this;
+  }
+
+  public Block<T> build() {
+    return new Block<>(id, minerId, hashPreviousBlock, hash, timestamp, magicNumber);
+  }
+}

src/blockchain/Blockchain.java

@@ -0,0 +1,239 @@
+package blockchain;
+
+import blockchain.crypto.SignValidator;
+import blockchain.data.SignedData;
+import blockchain.data.format.DataFormatter;
+import blockchain.io.Persister;
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.Date;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;
+import java.util.function.BiFunction;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class Blockchain<T extends SignedData & Serializable> {
+
+  private static final Long ACCEPTABLE_TIME = TimeUnit.SECONDS.toMillis(5);
+
+  private final ReentrantReadWriteLock readWritelock;
+
+  private final List<Block<T>> blocks;
+  private final List<T> pendingMessages;
+  private final Persister persister;
+
+  private int prefixLength;
+  private DataFormatter<T> dataFormatter;
+
+  private AtomicInteger idGenerator;
+  private BiFunction<Integer, String, Optional<T>> systemFeedback;
+
+  public Blockchain(Persister<T> persister, DataFormatter<T> dataFormatter,
+      SystemFeedback<T> systemFeedback) {
+    this.systemFeedback = systemFeedback;
+    this.readWritelock = new ReentrantReadWriteLock();
+    this.persister = persister;
+    this.dataFormatter = dataFormatter;
+    this.prefixLength = 0;
+    List<Block<T>> fileBlocks = persister.load();
+    if (!fileBlocks.isEmpty() && validateAllChain(fileBlocks)) {
+      this.blocks = fileBlocks;
+    } else {
+      this.blocks = new LinkedList<>(Collections.singleton(
+          new BlockBuilder<T>()
+              .withId(1)
+              .withMinerId(0L)
+              .withHashPreviousBlock("")
+              .withHash("0")
+              .withMagicNumber(0)
+              .withTimestamp(new Date().getTime()).build()));
+      persister.save(fileBlocks);
+    }
+    pendingMessages = new LinkedList<>();
+    this.idGenerator = new AtomicInteger(blocks.get(blocks.size() - 1).getId() + 1);
+  }
+
+  public void accept(Block<T> newBlock) {
+    WriteLock writeLock = readWritelock.writeLock();
+    try {
+      writeLock.lock();
+      if (isValid(newBlock)) {
+        applyFeedback(String.format("miner%d", newBlock.getMinerId()));
+        newBlock.setData(new ArrayList<>(pendingMessages));
+        outputAndAdjust(newBlock);
+        blocks.add(newBlock);
+        pendingMessages.clear();
+        persister.save(blocks);
+      }
+    } finally {
+      writeLock.unlock();
+    }
+  }
+
+  public boolean appendData(T data) {
+    WriteLock writeLock = readWritelock.writeLock();
+    try {
+      writeLock.lock();
+      if (isSigned(data) && dataIdentityValid(data)) {
+        return pendingMessages.add(data);
+      }
+    } finally {
+      writeLock.unlock();
+    }
+    return false;
+  }
+
+  public String getPrefix() {
+    ReadLock readLock = readWritelock.readLock();
+    try {
+      readLock.lock();
+      return Stream.iterate("0", x -> "0")
+          .limit(prefixLength)
+          .reduce("", (x, y) -> x + y);
+    } finally {
+      readLock.unlock();
+    }
+  }
+
+  public Block<T> tail() {
+    ReadLock readLock = readWritelock.readLock();
+    try {
+      readLock.lock();
+      return blocks.get(blocks.size() - 1);
+    } finally {
+      readLock.unlock();
+    }
+  }
+
+  public Integer uniqueIdentity() {
+    return idGenerator.incrementAndGet();
+  }
+
+  public Stream<T> data() {
+      return new ArrayList<>(blocks).stream()
+          .map(Block::getData)
+          .filter(List::isEmpty)
+          .flatMap(Collection::stream);
+  }
+
+  private boolean isSigned(T data) {
+    try {
+      SignValidator signValidator = new SignValidator(data.publicKey());
+      return signValidator.verifySignature(data.raw(), data.dataSignature());
+    } catch (Exception e) {
+      return false;
+    }
+  }
+
+  private boolean isValid(Block newBlock) {
+    Block tailBlock = blocks.get(blocks.size() - 1);
+    if (!newBlock.getHash().startsWith(getPrefix()) || !Objects
+        .equals(newBlock.getHashPreviousBlock(), tailBlock.getHash())) {
+      return false;
+    }
+    return true;
+  }
+
+  private void outputAndAdjust(Block<T> newBlock) {
+    outputStats(newBlock);
+    adjustComplexity(newBlock);
+  }
+
+  private void outputStats(Block<T> newBlock) {
+    System.out.printf("Block:\n");
+    System.out.printf("Id: %s\n", newBlock.getId());
+    System.out.printf("Created by miner # %s\n", newBlock.getMinerId());
+    System.out.printf("Timestamp: %s\n", newBlock.getTimestamp());
+    System.out.printf("Magic number: %s\n", newBlock.getMagicNumber());
+    System.out.printf("Hash of the previous block:\n%s\n", newBlock.getHashPreviousBlock());
+    System.out.printf("Block data: \n%s\n", newBlock.getData().stream().map(
+        x -> dataFormatter.format(x)
+    ).collect(Collectors.joining("\n")));
+    System.out.printf("Magic number: %s\n", newBlock.getMagicNumber());
+    System.out
+        .printf("Block was generating for: %s seconds\n", getGenerationTime(newBlock) / 1000);
+  }
+
+  private void adjustComplexity(Block<T> newBlock) {
+    if (!withinAcceptable(newBlock)) {
+      if (ACCEPTABLE_TIME < getGenerationTime(newBlock)) {
+        if (prefixLength > 0) {
+          prefixLength--;
+        }
+        System.out.printf("N was decreased to %s\n\n", prefixLength);
+      } else {
+        prefixLength++;
+        System.out.printf("N was increased to %s\n\n", prefixLength);
+      }
+    } else {
+      System.out.printf("N stays the same\n\n");
+    }
+  }
+
+  private Long getGenerationTime(Block<?> newBlock) {
+    return tail() == null ? 0 : (newBlock.getTimestamp() - tail().getTimestamp());
+  }
+
+  private boolean withinAcceptable(Block<?> newBlock) {
+    return Math.abs(getGenerationTime(newBlock) - ACCEPTABLE_TIME) <= 1000;
+  }
+
+  private boolean validateAllChain(List<Block<T>> blocks) {
+    for (int i = 1; i < blocks.size(); i++) {
+      Block<T> prev = blocks.get(i - 1);
+      Block<T> cur = blocks.get(i);
+      Stream<T> concatData = Stream.concat(
+          Objects.requireNonNullElse(prev.getData(), new ArrayList<T>()).stream(),
+          Objects.requireNonNullElse(cur.getData(), new ArrayList<T>()).stream());
+      if (!Objects.equals(prev.getHash(), cur.getHashPreviousBlock())
+          && dataIdentityValid(concatData.collect(Collectors.toList()))) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  private boolean dataIdentityValid(List<T> jointBlocks) {
+    for (int i = 1; i < jointBlocks.size(); i++) {
+      if (Objects.compare(jointBlocks.get(i - 1), jointBlocks.get(i),
+          Comparator.comparing(T::id)) > 0) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  private boolean dataIdentityValid(T data) {
+    Optional<T> lastEntry = getLastEntry();
+    return lastEntry
+        .map(t -> t.id() < data.id())
+        .orElse(true);
+  }
+
+  private Optional<T> getLastEntry() {
+    return blocks.stream()
+        .map(Block::getData)
+        .filter(List::isEmpty)
+        .flatMap(Collection::stream)
+        .limit(1)
+        .findFirst();
+  }
+
+  private void applyFeedback(String miner) {
+    Optional<T> feedback = systemFeedback.apply(uniqueIdentity(), miner);
+    feedback.ifPresent(
+        this::appendData
+    );
+  }
+}