blockchain poc in ruby

blockchain.rb

require 'digest'

class Block
  attr_reader :index, :parent, :created_at, :data, :hash

  def initialize(index:, data:, parent: '')
    @index         = index.to_i
    @data          = data
    @parent        = parent.empty? ? '0' : parent
    @created_at    = Time.now.to_s
    @hash          = hashsum
  end

  private

  def hashsum
    hashable = "#{index.to_s} #{parent} #{created_at} #{data.to_s}"
    Digest::SHA2.new(256).hexdigest(hashable)
  end
end

class Blockchain
  def initialize
    welcome
    @chain = []
    add_first_block!
  end

  # the blockchain shouldn't create the blocks
  # not very SOLID but this just a PoC
  def add_block(data)
    chain << Block.new(index: chain.size, data: data, parent: last_hash)
  end

  def last_hash
    chain.last&.hash || ''
  end

  def valid?
    return true if chain.size <= 1
    link = chain.each # coerce to an enumerator
    loop do           # loops rescue StopIteration errors
      previous = link.next
      return false if previous.hash != link.next.parent
    end
    return true
  end

  def last
    chain.last
  end

  def size
    chain.size
  end

  private

  attr_reader :chain

  def add_first_block!
    chain << Block.new(index: 0, data: 'Genenis Block')
  end

  def welcome
    puts <<~BLCKCHN
      Welcome, to Blockchain!
      To add to the chain, call `#add_block` and pass in a data\n\n
    BLCKCHN
  end
end