Blockchain.sm

#!/usr/bin/ruby

# Code translated from:
#   https://github.com/Savjee/SavjeeCoin

include SigningKey
import SigningKey::SigningKey

class Transaction(fromAddress, String toAddress, Number amount) {

    has timestamp = Date()
    has signature = nil

    # Creates a SHA256 hash of the transaction
    -> calculateHash() -> String {
        [fromAddress, toAddress, amount, timestamp].dump.sha256
    }

    /*
     * Signs a transaction with the given signingKey (which is an Elliptic keypair
     * object that contains a private key). The signature is then stored inside the
     * transaction object and later stored on the blockchain.
    */
    -> signTransaction(SigningKey signingKey) {

        # You can only send a transaction from the wallet that is linked to your
        # key. So here we check if the fromAddress matches your publicKey
        if (signingKey.getPublic != fromAddress) {
            die('You cannot sign transactions for other wallets!')
        }

        # Calculate the hash of this transaction, sign it with the key
        # and store it inside the transaction obect
        const hashTx = self.calculateHash
        const sig = signingKey.sign(hashTx)

        signature = sig
    }

    /**
    * Checks if the signature is valid (transaction has not been tampered with).
    * It uses the fromAddress as the public key.
    */
    -> isValid() -> Bool {
        # If the transaction doesn't have a from address we assume it's a
        # mining reward and that it's valid. You could verify this in a
        # different way (special field for instance)
        if (fromAddress == nil) {
            return true
        }

        if (signature == nil) {
            die ('No signature in this transaction');
        }

        SigningKey().keyFromPublic(fromAddress).verify(signature, self.calculateHash)
    }
}

class Blockchain::Block (Date timestamp, Array transactions, String previousHash = '') {

    has nonce = 0
    has hash = nil

    method init {
        hash = self.calculateHash
    }

    /**
    * Returns the SHA256 of this block (by processing all the data stored
    * inside this block)
    */
    -> calculateHash() -> String {
        [previousHash, timestamp, transactions, nonce].dump.sha256
    }

    /**
    * Starts the mining process on the block. It changes the 'nonce' until the hash
    * of the block starts with enough zeros (= difficulty)
    */
    -> mineBlock(Number difficulty) {
        var target_prefix = "0"*difficulty

        while (hash.first(difficulty) != target_prefix) {
            ++nonce
            hash = self.calculateHash
        }

        STDERR.say("Block mined: #{hash}")
    }

    /**
    * Validates all the transactions inside this block (signature + hash) and
    * returns true if everything checks out. False if the block is invalid.
    */
    -> hasValidTransactions() -> Bool {
        transactions.all { .isValid }
    }
}

class Blockchain (Number difficulty = 2, Array pendingTransactions = [], Number miningReward = 100) {

    has chain = []

    method init {
        chain = [self.createGenesisBlock]
    }

    -> createGenesisBlock() -> Blockchain::Block {
        Blockchain::Block(Date.parse('2021-10-07', '%Y-%m-%d'), [], '0')
    }

    /**
    * Returns the latest block on our chain. Useful when you want to create a
    * new Block and you need the hash of the previous Block.
    */
    -> getLatestBlock() -> Blockchain::Block {
        chain.last
    }

    /**
    * Takes all the pending transactions, puts them in a Block and starts the
    * mining process. It also adds a transaction to send the mining reward to
    * the given address.
    */
    -> minePendingTransactions(String miningRewardAddress) {
        const rewardTx = Transaction(nil, miningRewardAddress, miningReward)
        pendingTransactions.push(rewardTx)

        const block = Blockchain::Block(Date.now, pendingTransactions, self.getLatestBlock.hash)
        block.mineBlock(difficulty)

        STDERR.say('Block successfully mined!')
        chain.push(block)
        pendingTransactions = []
    }

    /**
    * Add a new transaction to the list of pending transactions (to be added
    * next time the mining process starts). This verifies that the given
    * transaction is properly signed.
    */
    -> addTransaction(Transaction transaction) {
        if (!transaction.fromAddress || !transaction.toAddress) {
            die('Transaction must include from and to address')
        }

        # Verify the transaction
        if (!transaction.isValid()) {
            die('Cannot add invalid transaction to chain')
        }

        if (transaction.amount <= 0) {
            die('Transaction amount should be higher than 0')
        }

        # Making sure that the amount sent is not greater than existing balance
        if (self.getBalanceOfAddress(transaction.fromAddress) < transaction.amount) {
            die('Not enough balance')
        }

        pendingTransactions.push(transaction)
        self
    }

    /**
    * Returns the balance of a given wallet address.
    */
    -> getBalanceOfAddress(String address) -> Number {
        var balance = 0;

        chain.each {|block|
            block.transactions.each {|trans|
                if (trans.fromAddress == address) {
                    balance -= trans.amount
                }

                if (trans.toAddress == address) {
                    balance += trans.amount
                }
            }
        }

        return balance
    }

    /**
    * Returns a list of all transactions that happened
    * to and from the given wallet address.
    */
    -> getAllTransactionsForWallet(String address) -> Array {
        var txs = []

        chain.each {|block|
            block.transactions.each {|tx|
                if ((tx.fromAddress == address) || (tx.toAddress == address)) {
                    txs.push(tx)
                }
            }
        }

        STDERR.printf("get transactions for wallet count: %s\n", txs.length)
        return txs
    }

    /**
    * Loops over all the blocks in the chain and verify if they are properly
    * linked together and nobody has tampered with the hashes. By checking
    * the blocks it also verifies the (signed) transactions inside of them.
    */
    -> isChainValid() -> Bool {

        # Check if the Genesis block hasn't been tampered with by comparing
        # the output of createGenesisBlock with the first block on our chain
        if (self.createGenesisBlock.dump != chain.first.dump) {
            return false
        }

        # Check the remaining blocks on the chain to see if there hashes and
        # signatures are correct
        chain.each_cons(2, {|previousBlock, currentBlock|

            if (previousBlock.hash != currentBlock.previousHash) {
                return false
            }

            if (!currentBlock.hasValidTransactions) {
                return false
            }

            if (currentBlock.hash != currentBlock.calculateHash) {
                return false
            }
        })

        return true
    }
}