The ability to generate an ULID from a legacy integer ID. Useful for syncing data between systems.

example.rb

require 'time'
class User
  def id
    '507f1f77bcf86cd799439011'
  end

  def created_at
    Time.parse('2017-04-24 12:15:20 +0200')
  end
end

user = User.new

ulid = CustomULID.generate("Legacy::Ea2::#{user.class}", user.id, user.created_at)
puts ulid
ulid2 = CustomULID.generate("Legacy::Ea2::#{user.class}", user.id, user.created_at)
puts ulid2

puts ulid == ulid2


ulid3 = CustomULID.generate("Legacy::Ea2::#{user.class}", '507f191e810c19729de860ea', user.created_at)
puts ulid3
puts ulid == ulid3
puts CustomULID.generate("Legacy::Ea2::Person", '507f191e810c19729de860ea', user.created_at)

generate_ulid.rb

require 'digest/sha1'
class CustomULID
  ENCODING = '0123456789ABCDEFGHJKMNPQRSTVWXYZ' # Crockford's Base32
  RANDOM_BYTES = 10
  ENCODED_LENGTH = 26
  BIT_LENGTH = 128
  BITS_PER_B32_CHAR = 5

  MASK = 0x1f

  def self.generate(class_name, id, created_at)
    time = [(created_at.to_f * 10_000).to_i].pack("Q>")[2..-1]
    word = [id, Digest::SHA1.hexdigest(class_name)].pack("a5a5")
    bytes = (time + word)
    (hi, lo) = bytes.unpack("Q>Q")
    input = (hi << 64) | lo

    (1..ENCODED_LENGTH).to_a.reduce("") do |s, n|
      shift = BIT_LENGTH - BITS_PER_B32_CHAR * n
      s + ENCODING[(input >> shift) & MASK]
    end
  end
end