const crypto = require('crypto');

const hashGenerator = (...inputs) => {
    const hash = crypto.createHash('sha256');
    hash.update(inputs.map(item => JSON.stringify(item)).join(''));
    return hash.digest('hex');
}

class Block {
    constructor(timestamp, lastHash, hash, data, nonce) {
        this.timestamp = timestamp;
        this.lastHash = lastHash;
        this.hash = hash;
        this.data = data;
        this.nonce = nonce;
    }
    
    static createGenesis() {
        return new this("17/01/2020", "dummy-last-hash", "dummy-hash", "data in genesis block", 0)
    }

static createBlock(previousBlock, data) {
        let hash, timestamp, nonce=0;
        const lastHash = previousBlock.hash;
        do {
            timestamp = Date.now();
            nonce++;
            hash = hashGenerator(timestamp, lastHash, data, nonce);
        } while (hash.substr(0,4) !== '0'.repeat(4));
        
        return new this(timestamp, lastHash, hash, data, nonce);
    }

}

class Blockchain {
    constructor() {
        this.blocks = [Block.createGenesis()];
    }
    
    addBlock(data) {
        const createdBlock = Block.createBlock(this.blocks[this.blocks.length - 1], data);
        this.blocks.push(createdBlock);
    }

}

const webbyChain = new Blockchain();
webbyChain.addBlock('This dummy data is saved in the second block of the webbyChain');
webbyChain.addBlock('This immutable data is saved in the third block');
webbyChain.addBlock('Adding top secret in the fourth block');
console.log(webbyChain.blocks);