A blockchain demo

blockchain.js

const tracer = require('tracer').colorConsole()
const console = tracer
const bitcoin = require('bsv')

const maxTried = 100000//Number.MAX_VALUE
class Block {
    constructor(data, previousHash, difficulty) {
        this.data = data.toString()
        this.previousHash = previousHash
        this.timestamp = Date.now().toString()
        this.difficulty = difficulty
        this.mine()
    }

    hash256() {
        const str = this.previousHash + this.data + this.timestamp + this.answer.toString()
        return bitcoin.crypto.Hash.sha256(Buffer.from(str, 'utf8')).toString('hex')
    }

    mine() {
        this.answer = -1
        do {
            this.answer++
            if(this.answer >= maxTried) {
                throw Error('No Answer')
            }
            this.hash = this.hash256()
        } while(this.hash.substr(0, this.difficulty) !== '0'.repeat(this.difficulty))
    }


}

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

    isValid() {
        for(let i=1; i<this.chain.length; i++) {
            const currentBlock = this.chain[i]
            const previoudBlock = this.chain[i-1]
            if(currentBlock.hash != currentBlock.hash256()) {
                console.debug(currentBlock.hash, currentBlock.hash256())
                return false
            }
            if(previoudBlock.hash != currentBlock.previousHash) {
                console.debug(previoudBlock.hash, currentBlock.previousHash)
                return false
            }
            if(currentBlock.hash.substr(0, currentBlock.difficulty) !== '0'.repeat(currentBlock.difficulty)) {
                console.debug(currentBlock.hash.substr(0, currentBlock.difficulty) , '0'.repeat(currentBlock.difficulty))
                return false
            }
        }
        return true
    }

    append(data, difficulty) {
        const newBlock = new Block(data, this.chain[this.chain.length-1].hash, difficulty)
        this.chain.push(newBlock)
    }

}

const genesisBlock = new Block('Born', 0, 0)
const blockchain = new Blockchain(genesisBlock)

blockchain.append('Love', 1)
blockchain.append('Marry', 2)
blockchain.append('Life', 3)
blockchain.append('How to change your wife(life) in 21 days', 5)

console.log(blockchain.chain)
console.log(blockchain.isValid())