main.js

const SHA256 = require('crypto-js/sha256');

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

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.transactions) + 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);
    }

}

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

    createGenesisBlock() {
        return new Block("04/03/2022", "Initiate", "0");
    }

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

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

        console.log('Block successfully mined!');
        this.chain.push(block);

        this.pendingTransactions = [
            new transaction(null, miningRewardAddress, this.miningReward)
        ];
    }

    createTransaction(transaction) {
        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.hash !== currentBlock.calculateHash()) {
                return false;
            }

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


}

let skyCoin = new Blockchain();

skyCoin.createTransaction(new transaction('address1', 'address2', 100));
skyCoin.createTransaction(new transaction('address2', 'address1', 50));


console.log('\n Starting the miner...');
skyCoin.minePendingTransactions('address1');

console.log('\n Balance of skycoin-address is', skyCoin.getBalanceOfAddress('address1'));

//console.log('Is blockchain valid? ' + skyCoin.isChainValid());

//console.log(JSON.stringify(skyCoin, null, 4));