blockchain

blockchain.es6.js

const RushaClass = require('Rusha');
const rusha = new RushaClass();

const CONFIG = { difficulty: 3 }

// from: https://bitcoin.org/bitcoin.pdf
// and: https://www.igvita.com/2014/05/05/minimum-viable-block-chain/
// I do sha1 instead of sha256 here for performance

class Block {
  constructor({ prevHash = 0, timestamp = null, nonce = 0, body = "", hash = "", height = 0 }) {
    this.prevHash = prevHash
    this.nonce = nonce
    this.body = body
    this.hash = hash
    this.height = height
    this.timestamp = (timestamp || new Date().getTime())
  }

  static fromString(blockString){
    return new Block(JSON.parse(blockString))
  }

  difficulty() {
    return this.hash.search(/[1-9a-zA-Z]/) // serch for none 0
  }

  get data() {
    return { 
      prevHash: this.prevHash, 
      nonce: this.nonce, 
      height: this.height, 
      timestamp: this.timestamp, 
      body: this.body 
    }
  }

  generateHash() {
    this.hash = rusha.digestFromString(this.toString())
    return this.hash
  }

  mine() {
    let attempts = 0;
    while(!this.isValid()){
      this.nonce = rusha.digestFromString(Math.random().toString())
      this.generateHash();
      attempts++
    }
    
    // console.log(`Mined "${this.body}" block after ${attempts} tries`)
    return { attempts }
  }

  isValid() {
    return this.difficulty() >= CONFIG.difficulty
  }

  toString() {
    return JSON.stringify({ ...this.data, hash: this.hash })
  }
}


class Blockchain {
  constructor(blocks) {
    this.blocks = blocks
  }

  static fromString(blockchain_dump) {
    return blockchain_dump.split("\n")
                   .map(b => { return Block.fromString(b) })
  }

  length() {
    return this.blocks.length
  }

  toString() {
    return this.blocks.map(b => { return b.toString() })
               .join("\n")
  }
  
  // review the entire blockchain and ensure it's valid
  mine() {
    for (var i = 0; i < this.blocks.length; i++) {
      if (i == 0) continue // genesis
      
      let currentBlock = this.blocks[i]
      let prevBlock = this.blocks[i - 1]

      if (currentBlock.prevHash != prevBlock.hash) {
        console.log(`correcting block sequence to ${prevBlock.body}->${currentBlock.body}`)
        currentBlock.prevHash = prevBlock.hash
      }

      currentBlock.mine()
    }
  }

  // this function might invalidate the blockchain
  append(block) {
    let tailBlock = this.blocks[this.blocks.length - 1]

    block.prevHash = tailBlock.hash
    block.height = this.blocks.length

    if (! block.isValid()) block.mine()

    this.blocks.push(block)

    return this
  }
}

let genesisBlock = new Block({ 
  prevHash: "0", 
  nonce: "919ddb02165d3c490133e479d1955b08ad3ab0cb", 
  hash: "000cc64a0037f5a29d4f18736d201c7cd38c696c",
  height: 0,
  timestamp: 1,
  body: "The Genesis block" 
})

let blockchain = new Blockchain([ genesisBlock ])

blockchain.append(new Block({ body: "An extension block" }))
blockchain.append(new Block({ body: "maybe an action in here?" }))
blockchain.append(new Block({ body: "then a reaction in here" }))
blockchain.append(new Block({ body: "one last block" }))

blockchain.mine()

console.log(
  `Blockchain started`,
  blockchain
);