Simple blockchain in crystal

crystal_blockchain.cr

require "secure_random"
require "openssl"

module Blockchain
  extend self

  @@blocks = Array(String).new

  def init_blockchain
    data = SecureRandom.hex(8)
    timestamp = Time.new
    previous_hash = "0"
    index = 0
    hash_block(data, timestamp, previous_hash, index)
  end

  def add_new_block(data : String)
    index = @@blocks.size
    previous_hash = get_last_hash
    hash_block(data, Time.new, previous_hash, index)
  end

  def get_all_blocks
    @@blocks
  end

  private def hash_block(data : String, timestamp : Time, previous_hash : String, index : Int32 | Int64)
    hash = ""
    noonce = 0

    loop do
      break if is_hash_valid?(hash)
      digest = OpenSSL::Digest.new("SHA256")
      digest << "#{data}#{timestamp}#{previous_hash}#{index}#{noonce}"
      hash = digest.hexdigest
      noonce = noonce + 1
    end

    @@blocks.push(hash)
  end

  private def is_hash_valid?(hash)
    # difficulty
    hash.starts_with?("0000")
  end

  private def get_last_hash
    @@blocks[-1]
  end
end

Blockchain.init_blockchain

10.times do
  Blockchain.add_new_block(SecureRandom.hex(8))
end

puts Blockchain.get_all_blocks