blockchain.js

const Block = require('./block');
const cryptoHash = require('./crypto-hash');

class Blockchain {
    constructor() {
        this.chain = [Block.genesis()];
    }

    addBlock({ data }) {
        const lastBlock = this.getLastBlock();
        const newBlock = Block.mineBlock({
            lastBlock,
            data
        });
        this.chain.push(newBlock);
    }

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

    replaceChain(chain) {
        if(chain.length <= this.chain.length) {
            console.error('The incoming chain must be longer');
            return;
        }

        if(!Blockchain.isValidChain(chain)) {
            console.error('The incoming chain must be valid');
            return;
        }
        console.log('replacing chain with', chain);
        this.chain = chain;
    }

    static isValidChain(chain) {
        if(JSON.stringify(chain[0]) !== JSON.stringify(Block.genesis()))
        {
            return false;
        }

        for(let i=1; i<chain.length; i++) {
            const { timestamp, lastHash, hash, nonce, difficulty, data } = chain[i];           
            const actualLastHash = chain[i-1].hash;
            const lastDifficulty = chain[i-1].difficulty;

            if(lastHash !== actualLastHash) {
                return false;
            }

            const validatedHash = cryptoHash(timestamp, lastHash, data, nonce, difficulty);

            if(hash !== validatedHash) {
                return false;
            }

            if(Math.abs(lastDifficulty - difficulty) > 1) {
                return false;
            }
        }
        return true;
    }
}

module.exports = Blockchain;