philCoin

main.js

// import of library for hash functions
const SHA256 = require('crypto-js/sha256');

// class to determine what the blockchain will look like
class Block {/*  */
    // data would store terms of currency would store sender and receiver information
    // previoushash ensure integrity of data
    constructor(index, timestamp, data, previoushash = '') {
        this.index = index;
        this.timestamp = timestamp;
        this.data = data;
        this.previoushash = previoushash;
        // hash of our block calculation
        this.hash = this.calculateHash();
    }
a
    // method to identify block on chain
    // using .toString otherwise it returns an object, more readable
    calculateHash() {
        return SHA256(this.index + this.previoushash + this.timestamp + JSON.stringify(this.data)).toString();
    }
}


class Blockchain {
    // responsible for initializing the blockchain
    constructor() {
        // area of blocks
        this.chain = [this.createGenesisBlock()];
    }

    // first block should be added manually
    createGenesisBlock() {
        return new Block(0, "01/01/2017", "Gensis block", "0");
    }

    // returns latest block in the chain, returning the last element
    getLatestBlock() {
        return this.chain[this.chain.length - 1];
    }

    // pushes block onto the array, 'chain'
    addBlock(newBlock) {
            // must set the hash first
            newBlock.previoushash = this.getLatestBlock().hash;
            // must recalculate for new chain with a new hash function
            newBlock.hash = newBlock.calculateHash();
            this.chain.push(newBlock);
        }
        // check validity of the chain by looping through it comparing hashes
    isChainValid() {
        for (let i = 1; i < this.chain.length; i++) {
            const currentBlock = this.chain[i];
            const previousBlock = this.chain[i - 1];

            //check if hash of currentBlock is still valid
            if (currentBlock.hash !== currentBlock.calculateHash()) {
                return false;
            }

            //check if block points to correct previousBlock            
            if (currentBlock.previoushash !== previousBlock.hash) {
                return false;
            }
        }

        return true;
    }
}

// instance of the block, to test
let philCoin = new Blockchain();
philCoin.addBlock(new Block, (1, "10/07/2017", { amount: 4 }));
philCoin.addBlock(new Block, (2, "11/07/2017", { amount: 10 }));


// data tampering example, adding tokens to override data
philCoin.chain[1].data = { amount: 100 };
// attempt tamper by recalcualting the hash
philCoin.chain[1].hash = philCoin.chain[1].calculateHash();

console.log(JSON.stringify(philCoin, null, 4));

// data tampering makes false
console.log(' Is chain valid? ' + philCoin.isChainValid());