Stripped-down implementation of a blockchain

blocky.rb

require 'date'
require 'digest'

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

  def initialize(data:, parent:, author:)
    raise ArgumentError.new '`data` should respond to `to_s`' unless data.respond_to?(:to_s)
    raise ArgumentError.new '`author` should respond to `to_s`' unless author.respond_to?(:to_s)

    unless parent.nil? || parent.is_a?(Block)
      raise ArgumentError.new '`parent` should be an instance of `Block` or `nil`'
    end

    @data = data
    @parent = parent
    @author = author
    @created_at = DateTime.now
    @hash = [@data.to_s, @author.to_s, @created_at.to_s]
    @hash << @parent.hash if @parent

    @hash = Digest::SHA256.hexdigest(@hash.join)
  end

  def to_s
    s = "#{@hash}\n"
    s += "Created at: #{@created_at.to_s}\n"
    s += "Parent: #{@parent.hash}\n" if @parent
    s += "Author: #{@author}\n" if @author
    s += "\n"

    data_string = @data

    while data_string.length > 76 do
      s += "    #{data_string.slice!(0, 76)}\n"
    end

    s
  end
end

class BlockChain
  attr_reader :head

  def initialize(block = nil)
    unless block.nil? || block.is_a?(Block)
      raise ArgumentError '`block` should be an instance of `Block` or `nil`'
    end

    @head = block if block
  end

  def <<(block)
    unless block.is_a?(Block)
      raise ArgumentError.new '`block` should be an instance of `Block`'
    end

    unless @head == block.parent
      raise ArgumentError.new "`block`'s parent doesn't match the chain's head"
    end

    @head = block
  end
end

chain = BlockChain.new

b = Block.new(
  data: "Lorem ipsum dolor amet vegan stumptown copper mug chicharrones scenester small batch plaid viral flannel. Microdosing meh vice kale chips kitsch. Edison bulb bushwick man braid, farm-to-table aesthetic cornhole whatever everyday carry sustainable four loko brooklyn cred. Yuccie typewriter raw denim leggings. 90's tote bag everyday carry before they sold out. Selvage knausgaard etsy, sartorial gastropub migas vinyl sustainable vegan cornhole seitan cred.",
  parent: chain.head,
  author: "Sergio")

chain << b

b2 = Block.new(
  data: "Synth truffaut palo santo bicycle rights swag plaid pork belly mustache fingerstache selvage banjo asymmetrical brooklyn enamel pin biodiesel. Heirloom vape kale chips sustainable. Health goth polaroid edison bulb, succulents marfa squid you probably haven't heard of them. Crucifix franzen kitsch, lomo pok pok pug bicycle rights shaman. Chillwave letterpress twee, poke thundercats kombucha snackwave gentrify lyft blue bottle cold-pressed celiac offal. Portland messenger bag paleo semiotics art party flannel.",
  parent: chain.head,
  author: "Sergio"
)

chain << b2

b3 = Block.new(
  data: "Synth truffaut palo santo bicycle rights swag plaid pork belly mustache fingerstache selvage banjo asymmetrical brooklyn enamel pin biodiesel. Heirloom vape kale chips sustainable. Health goth polaroid edison bulb, succulents marfa squid you probably haven't heard of them. Crucifix franzen kitsch, lomo pok pok pug bicycle rights shaman. Chillwave letterpress twee, poke thundercats kombucha snackwave gentrify lyft blue bottle cold-pressed celiac offal. Portland messenger bag paleo semiotics art party flannel.",
  parent: chain.head,
  author: "Sergio"
)

chain << b3

block = chain.head

while block do
  puts block
  puts

  block = block.parent
end