commit 8666ad8752bd6afb083e163b7a537541bd423d40
Author: Aelita4 <kontakt@mikorosa.pl>
Date:   Wed Jan 4 22:15:07 2023 +0100

    Initial commit

diff --git a/.gitignore b/.gitignore
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--- /dev/null
+++ b/.gitignore
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+### IntelliJ IDEA ###
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+target/
+.idea/
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store
\ No newline at end of file
diff --git a/DzieCoin.iml b/DzieCoin.iml
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index 0000000..b1c395b
--- /dev/null
+++ b/DzieCoin.iml
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+<?xml version="1.0" encoding="UTF-8"?>
+<module org.jetbrains.idea.maven.project.MavenProjectsManager.isMavenModule="true" type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" LANGUAGE_LEVEL="JDK_19">
+    <output url="file://$MODULE_DIR$/target/classes" />
+    <output-test url="file://$MODULE_DIR$/target/test-classes" />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src/main/java" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/src/main/resources" type="java-resource" />
+      <sourceFolder url="file://$MODULE_DIR$/src/test/java" isTestSource="true" />
+      <excludeFolder url="file://$MODULE_DIR$/target" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>
\ No newline at end of file
diff --git a/pom.xml b/pom.xml
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--- /dev/null
+++ b/pom.xml
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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>groupId</groupId>
+    <artifactId>DzieCoin</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <properties>
+        <maven.compiler.source>19</maven.compiler.source>
+        <maven.compiler.target>19</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+</project>
\ No newline at end of file
diff --git a/src/main/java/pl/mikorosa/dziecoin/Block.java b/src/main/java/pl/mikorosa/dziecoin/Block.java
new file mode 100644
index 0000000..d84ffd2
--- /dev/null
+++ b/src/main/java/pl/mikorosa/dziecoin/Block.java
@@ -0,0 +1,118 @@
+package pl.mikorosa.dziecoin;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Block {
+    private String hash;
+    private String prevHash;
+    private int height;
+    private List<Transaction> transactions;
+    private List<NFT> nfts;
+    private int nonce;
+
+    public Block() {
+        this.transactions = new ArrayList<>();
+        this.nfts = new ArrayList<>();
+    }
+
+    public Block(String prevHash, int height, List<Transaction> transactions) {
+        this.prevHash = prevHash;
+        this.height = height;
+        this.transactions = transactions;
+        this.nfts = new ArrayList<>();
+    }
+
+    public Block(String hash, String prevHash, int height, List<Transaction> transactions, List<NFT> nfts, int nonce) {
+        this.hash = hash;
+        this.prevHash = prevHash;
+        this.height = height;
+        this.transactions = transactions;
+        this.nfts = nfts;
+        this.nonce = nonce;
+    }
+
+    public void mineBlock() {
+        String blockStruct = this.prevHash + this.height;
+        for (Transaction transaction : this.transactions) {
+            blockStruct += transaction.toString();
+        }
+
+        for (NFT nft : nfts) {
+            blockStruct += nft.toString();
+        }
+
+        int nonce = 0;
+
+        String hash;
+
+        System.out.println();
+        while(true) {
+            hash = CalculateHash.sha256sum(blockStruct + nonce);
+            if(hash.startsWith("0".repeat(Main.difficulty))) break;
+            nonce++;
+            System.out.print("\rMining block " + height + "... " + nonce);
+        }
+
+        System.out.println("\nSuccessfully mined block " + height + " (nonce: " + nonce + ")");
+
+        this.hash = hash;
+        this.nonce = nonce;
+    }
+
+    public void addTransaction(Transaction transaction) {
+        transactions.add(transaction);
+    }
+
+    public void addNFT(NFT nft) {
+        nfts.add(nft);
+    }
+
+    public enum VerifyCodes {
+        SUCCESS,
+        INVALID_POW_SIGNATURE,
+        HASH_MISMATCH,
+        INVALID_BLOCK_HASH
+    }
+
+    public VerifyCodes verifyBlock() {
+        String blockStruct = this.prevHash + this.height;
+        for (Transaction transaction : this.transactions) {
+            blockStruct += transaction.toString();
+        }
+        for (NFT nft : nfts) {
+            blockStruct += nft.toString();
+        }
+        blockStruct += this.nonce;
+
+        String calculatedHash = CalculateHash.sha256sum(blockStruct);
+
+        if(!calculatedHash.equals(this.hash)) return VerifyCodes.INVALID_BLOCK_HASH;
+        if(!calculatedHash.startsWith("0".repeat(Main.difficulty))) return VerifyCodes.INVALID_POW_SIGNATURE;
+        return VerifyCodes.SUCCESS;
+    }
+
+    public List<Transaction> getTransactions() {
+        return transactions;
+    }
+
+    public int getHeight() {
+        return height;
+    }
+
+    public List<NFT> getNFTs() {
+        return nfts;
+    }
+
+    public String getHash() {
+        return hash;
+    }
+
+    public String getPrevHash() {
+        return prevHash;
+    }
+
+    public int getNonce() {
+        return nonce;
+    }
+}
diff --git a/src/main/java/pl/mikorosa/dziecoin/Blockchain.java b/src/main/java/pl/mikorosa/dziecoin/Blockchain.java
new file mode 100644
index 0000000..ab21fb0
--- /dev/null
+++ b/src/main/java/pl/mikorosa/dziecoin/Blockchain.java
@@ -0,0 +1,86 @@
+package pl.mikorosa.dziecoin;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Blockchain {
+    private List<Block> blocks;
+    private int length;
+
+    public Blockchain(String genesisBlockRecipient) {
+        blocks = new ArrayList<>();
+        length = blocks.size();
+
+        Transaction firstTransaction = new Transaction("0", genesisBlockRecipient, 10);
+        List<Transaction> transactions = new ArrayList<>();
+        transactions.add(firstTransaction);
+
+        Block genesisBlock = new Block("0", 1, transactions);
+
+        genesisBlock.mineBlock();
+        if(genesisBlock.verifyBlock() != Block.VerifyCodes.SUCCESS) throw new IllegalStateException("Genesis block is invalid");
+
+        try {
+            addBlock(genesisBlock);
+        } catch (BlockchainIntegrityException e) {
+            System.out.println("Blockchain Integrity Exception: " + e.getMessage());
+        }
+    }
+
+    public int getLength() {
+        return length;
+    }
+
+    public List<Block> getBlocks() {
+        return blocks;
+    }
+
+    public Block getLatestBlock() {
+        return blocks.get(length - 1);
+    }
+
+    public Block.VerifyCodes validateChain() {
+        for (int i = 1; i < (length - 1); i++) {
+            if(blocks.get(i).verifyBlock() != Block.VerifyCodes.SUCCESS) return blocks.get(i).verifyBlock();
+            if(!blocks.get(i).getHash().equals(blocks.get(i + 1).getPrevHash())) return Block.VerifyCodes.HASH_MISMATCH;
+        }
+
+        for (Block block : blocks) {
+            if(!block.getHash().startsWith("0".repeat(Main.difficulty))) return Block.VerifyCodes.INVALID_POW_SIGNATURE;
+        }
+
+        return Block.VerifyCodes.SUCCESS;
+    }
+
+    public void addBlock(Block block) throws BlockchainIntegrityException {
+        Block.VerifyCodes status = block.verifyBlock();
+
+        if(status == Block.VerifyCodes.HASH_MISMATCH) throw new BlockchainIntegrityException("Block " + block.getHeight() + " calculated hash and actual hash does not match");
+        if(status == Block.VerifyCodes.INVALID_POW_SIGNATURE) throw new BlockchainIntegrityException("Block " + block.getHeight() + " contains invalid proof of work signature");
+        if(status == Block.VerifyCodes.INVALID_BLOCK_HASH) throw new BlockchainIntegrityException("Block " + block.getHeight() + " contains invalid hash");
+
+        if(length != 0) { // don't check for very first block
+            if (!getLatestBlock().getHash().equals(block.getPrevHash())) throw new BlockchainIntegrityException("Block " + block.getHeight() + " previous hash does not match");
+
+            for (Transaction transaction : block.getTransactions()) {
+                if(this.getAddressBalance(transaction.getSender()) < transaction.getAmount())
+                    throw new BlockchainIntegrityException("Wallet " + transaction.getSender() + " at block " + block.getHeight() + " tried to spend too much\nBalance: " + this.getAddressBalance(transaction.getSender()) + "\nTried to spend: " + transaction.getAmount());
+            }
+        }
+        blocks.add(block);
+        length++;
+    }
+
+    public int getAddressBalance(String walletAddress) {
+        int amount = 0;
+
+        for (Block block : blocks) {
+            for (Transaction transaction : block.getTransactions()) {
+                if(transaction.getSender().equals(walletAddress)) amount -= transaction.getAmount();
+                if(transaction.getRecipient().equals(walletAddress)) amount += transaction.getAmount();
+            }
+        }
+
+        return amount;
+    }
+}
diff --git a/src/main/java/pl/mikorosa/dziecoin/BlockchainIntegrityException.java b/src/main/java/pl/mikorosa/dziecoin/BlockchainIntegrityException.java
new file mode 100644
index 0000000..466dba1
--- /dev/null
+++ b/src/main/java/pl/mikorosa/dziecoin/BlockchainIntegrityException.java
@@ -0,0 +1,8 @@
+package pl.mikorosa.dziecoin;
+
+public class BlockchainIntegrityException extends Exception {
+    public BlockchainIntegrityException(String message) {
+        super(message);
+    }
+}
+
diff --git a/src/main/java/pl/mikorosa/dziecoin/CalculateHash.java b/src/main/java/pl/mikorosa/dziecoin/CalculateHash.java
new file mode 100644
index 0000000..4f2be3a
--- /dev/null
+++ b/src/main/java/pl/mikorosa/dziecoin/CalculateHash.java
@@ -0,0 +1,45 @@
+package pl.mikorosa.dziecoin;
+
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+
+public abstract class CalculateHash {
+    public static String sha256sum(String input) {
+        MessageDigest md;
+
+        try {
+            md = MessageDigest.getInstance("SHA-256");
+        } catch(NoSuchAlgorithmException e) {
+            throw new IllegalArgumentException(e);
+        }
+
+        byte[] sha256sum = md.digest(input.getBytes(StandardCharsets.UTF_8));
+        StringBuilder sb = new StringBuilder();
+
+        for(byte b : sha256sum) {
+            sb.append(String.format("%02x", b));
+        }
+
+        return sb.toString();
+    }
+
+    public static String md5sum(String input) {
+        MessageDigest md;
+
+        try {
+            md = MessageDigest.getInstance("MD5");
+        } catch(NoSuchAlgorithmException e) {
+            throw new IllegalArgumentException(e);
+        }
+
+        byte[] md5sum = md.digest(input.getBytes(StandardCharsets.UTF_8));
+        StringBuilder sb = new StringBuilder();
+
+        for(byte b : md5sum) {
+            sb.append(String.format("%02x", b));
+        }
+
+        return sb.toString();
+    }
+}
diff --git a/src/main/java/pl/mikorosa/dziecoin/Main.java b/src/main/java/pl/mikorosa/dziecoin/Main.java
new file mode 100644
index 0000000..7b59f35
--- /dev/null
+++ b/src/main/java/pl/mikorosa/dziecoin/Main.java
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+package pl.mikorosa.dziecoin;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Main {
+    public static int difficulty;
+    public static Blockchain blockchain;
+
+    public static void main(String[] args) {
+        Wallet w1 = new Wallet();
+        Wallet w2 = new Wallet();
+        Wallet w3 = new Wallet();
+
+        difficulty = 4;
+        blockchain = new Blockchain(w1.getAddress());
+
+        NFT n1 = new NFT(w1.getAddress(), "licencja na wozek widlowy");
+
+        List<Transaction> t1 = new ArrayList<>();
+        t1.add(new Transaction(w1.getAddress(), w2.getAddress(), 5));
+
+        Block b1 = new Block(blockchain.getLatestBlock().getHash(), blockchain.getLength() + 1, t1);
+
+        b1.addNFT(n1);
+
+        b1.mineBlock();
+
+        try {
+            blockchain.addBlock(b1);
+        } catch (BlockchainIntegrityException e) {
+            System.out.println("Blockchain Integrity Exception: " + e.getMessage());
+        }
+
+        List<Transaction> t2 = new ArrayList<>();
+        t2.add(new Transaction(w1.getAddress(), w3.getAddress(), 2));
+        t2.add(new Transaction(w2.getAddress(), w3.getAddress(), 3));
+
+        Block b2 = new Block(blockchain.getLatestBlock().getHash(), blockchain.getLength() + 1, t2);
+        b2.mineBlock();
+
+        try {
+            blockchain.addBlock(b2);
+        } catch (BlockchainIntegrityException e) {
+            System.out.println("Blockchain Integrity Exception: " + e.getMessage());
+        }
+
+        for (Block block : blockchain.getBlocks()) {
+            System.out.println("Block " + block.getHeight() + ": " + block.getHash());
+            for (Transaction transaction : block.getTransactions()) {
+                System.out.println("    " + transaction.getSender() + " => " + transaction.getRecipient() + " - " + transaction.getAmount());
+            }
+        }
+
+        System.out.println("Balances:");
+        System.out.println("Wallet 1: " + blockchain.getAddressBalance(w1.getAddress()));
+        System.out.println("Wallet 2: " + blockchain.getAddressBalance(w2.getAddress()));
+        System.out.println("Wallet 3: " + blockchain.getAddressBalance(w3.getAddress()));
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/pl/mikorosa/dziecoin/NFT.java b/src/main/java/pl/mikorosa/dziecoin/NFT.java
new file mode 100644
index 0000000..83cfaf6
--- /dev/null
+++ b/src/main/java/pl/mikorosa/dziecoin/NFT.java
@@ -0,0 +1,42 @@
+package pl.mikorosa.dziecoin;
+
+public class NFT {
+    private String contract;
+    private String owner;
+    private String data;
+
+    public NFT(String owner, String data) {
+        this.owner = owner;
+        this.data = data;
+        this.contract = CalculateHash.md5sum(owner + data);
+    }
+
+    public NFT(String contract, String owner, String data) {
+        String testHash = CalculateHash.md5sum(owner + data);
+        if(!testHash.equals(contract)) throw new IllegalStateException("NFT contract and data does not match");
+        this.owner = owner;
+        this.data = data;
+        this.contract = contract;
+    };
+
+    public String getContract() {
+        return contract;
+    }
+
+    public String getOwner() {
+        return owner;
+    }
+
+    public String getData() {
+        return data;
+    }
+
+    @Override
+    public String toString() {
+        return "NFT{" +
+                "contract='" + contract + '\'' +
+                ", owner='" + owner + '\'' +
+                ", data='" + data + '\'' +
+                '}';
+    }
+}
diff --git a/src/main/java/pl/mikorosa/dziecoin/Transaction.java b/src/main/java/pl/mikorosa/dziecoin/Transaction.java
new file mode 100644
index 0000000..19ac6ea
--- /dev/null
+++ b/src/main/java/pl/mikorosa/dziecoin/Transaction.java
@@ -0,0 +1,34 @@
+package pl.mikorosa.dziecoin;
+
+public class Transaction {
+    private String sender;
+    private String recipient;
+    private int amount;
+
+    public Transaction(String sender, String recipient, int amount) {
+        this.sender = sender;
+        this.recipient = recipient;
+        this.amount = amount;
+    }
+
+    public String getSender() {
+        return sender;
+    }
+
+    public String getRecipient() {
+        return recipient;
+    }
+
+    public int getAmount() {
+        return amount;
+    }
+
+    @Override
+    public String toString() {
+        return "Transaction{" +
+                "sender='" + sender + '\'' +
+                ", recipient='" + recipient + '\'' +
+                ", amount=" + amount +
+                '}';
+    }
+}
diff --git a/src/main/java/pl/mikorosa/dziecoin/Wallet.java b/src/main/java/pl/mikorosa/dziecoin/Wallet.java
new file mode 100644
index 0000000..3c8286a
--- /dev/null
+++ b/src/main/java/pl/mikorosa/dziecoin/Wallet.java
@@ -0,0 +1,30 @@
+package pl.mikorosa.dziecoin;
+
+import java.security.*;
+
+public class Wallet {
+    private String address;
+    private PublicKey publicKey;
+    private PrivateKey privateKey;
+
+    Wallet() {
+        try {
+            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
+            keyGen.initialize(1024);
+            KeyPair keyPair = keyGen.genKeyPair();
+            privateKey = keyPair.getPrivate();
+            publicKey = keyPair.getPublic();
+            address = CalculateHash.md5sum(publicKey.getEncoded().toString());
+        } catch (NoSuchAlgorithmException e) {
+            System.out.println("No such algo: " + e);
+        } catch (ProviderException e) {
+            System.out.println("Provider exception: " + e);
+        } catch (Exception e) {
+            System.out.println("General exception: " + e);
+        }
+    }
+
+    public String getAddress() {
+        return address;
+    }
+}