blockchain.js

const SHA256  = require('crypto-js/sha256');
const EC = require('elliptic').ec;
const ec = new EC('secp256k1');

class Transaction{
    constructor(fromAddress, toAddress, amount) {
        this.fromAddress = fromAddress;
        this.toAddress = toAddress;
        this.amount = amount;
    }

    calculateHash(){
        return SHA256(this.fromAddress + this.toAddress + this.amount).toString();
    }

    signTransaction(signingKey){
        if(signingKey.getPublic('hex') !== this.fromAddress){
            throw new Error('You cannot sign transactions for other wallets!');
        }
        const hashTx = this.calculateHash();
        const sig = signingKey.sign(hashTx, 'base64');
        this.signature = sig.toDER('hex');
    }

    is_valid(){
        if(this.fromAddress === null) return true;

        //if there is signature extract public key next
        if(!this.signature || this.signature.length == 0){
            throw new Error('No signature in this transaction');
        }
        //Check if hash of the block is signed by the signature
        const publicKey = ec.keyFromPublic(this.fromAddress, 'hex');
        return publicKey.verify(this.calculateHash(), this.signature);
    }
}

class Block{
    constructor(timestamp, transactions, previousHash='') {
    this.timestamp = timestamp;
    this.transactions = transactions;
    this.previousHash = previousHash;
    this.hash = this.calculateHash();
    this.nonce = 0
    }

    calculateHash(){
        return SHA256(this.index + this.previousHash + this.timestamp + JSON.stringify(this.data) + this.nonce).toString();
    }

    mineBlock(difficulty){
        while(this.hash.substring(0, difficulty) !==  Array(difficulty + 1).join("0")){
            this.nonce++;
            this.hash = this.calculateHash();
        }
        console.log("Block mined: "+ this.hash);
    }

    hasValidTransactions(){
        for(const tx of this.transactions){
            if(!tx.is_valid()){
                return false;
            }
        }
        return true;
    }
}

class Blockchain {
    constructor(){
        this.chain = [this.createGenesisBlock()];
        this.difficulty = 2;
        this.pendingTransactions = [];
        this.miningReward = 100;
    }

    createGenesisBlock(){
        return new Block("01/01/2019", "Genesis Block", "0")
    }

    getLatestBlock(){
        return this.chain[this.chain.length-1]
    }

    minePendingTransactions(miningRewardAddress){
        let block = new Block(Date.now(), this.pendingTransactions, this.getLatestBlock().hash);
        block.mineBlock(this.difficulty);

        console.log('Block succesfully mined');
        this.chain.push(block);
        this.pendingTransactions = [
            new Transaction(null, miningRewardAddress, this.miningReward)
        ];
    }

    addTransaction(transaction){
        if(!transaction.fromAddress || !transaction.toAddress){
            throw new Error('Transaction must include from and to address');
        }
        console.log('transaction has theaddress')
        if(!transaction.is_valid()){
            throw new Error('Cannot add invalid transaction to chain');
        }

        this.pendingTransactions.push(transaction)
    }

    getBalanceOfAddress(address){
        let balance = 0;
        for(const block of this.chain){
            for(const trans of block.transactions){

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

            }
        }

        return balance;
    }

    isChainValid(){
        for(let i=1; i<this.chain.length; i++){
            const currentBlock = this.chain[i];
            const previousBlock = this.chain[i-1];

            if(!currentBlock.hasValidTransactions()){
                return false;
            }

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

        return true;
    }
}

module.exports.Blockchain = Blockchain
module.exports.Transaction = Transaction