Generator of random bank account numbers (Czech, CZ) / Generátor čísla bankovního účtu

random_account_generator.rb

# based on https://k3a.me/mod11.php
# limited to 10 digit account numbers

module RandomAccountGenerator
  WEIGHT = [1, 2, 4, 8, 5, 10, 9, 7, 3, 6].reverse.freeze

  class << self
    def call
      loop do
        account_number = guess_number
        return account_number if account_number
      end
    end

    def guess_number
      random_base   = rand(1_000_000_000..1_999_000_000)
      exploded_base = random_base.to_s.split('').map(&:to_i)
      pairs         = exploded_base.zip WEIGHT
      sum           = pairs.map { |i| i.inject(&:*) }.sum

      return random_base if sum % 11 == 0
    end
  end
end