invoice number generator

inoice_number_generator.rb

# generate invoice number in a sequential mode
# using redis and redlock gem
# ex:
# Accounting::InvoiceNumberGenerator::Base.new.lock do |next_number|
#.   # create your invoice here
# end
class Accounting::InvoiceNumberGenerator::Base
  LOCK_TIMEOUT = 10000
  FIRST_NUM_SEQUENCE = 100

  # pass the new generated invoice number to block
  def lock(&block)
    Invoice.transaction do
      lock_info = lock_manager.lock(lock_name, LOCK_TIMEOUT)
      if lock_info
        begin
          yield(get_next_number) if block_given?
        ensure
          lock_manager.unlock(lock_info)
        end
      else
        raise "LockTimeout #{lock_name}"
      end
    end
  end

  private

  # Warning: not thread safe
  def get_next_number
    "#{yearly_sequence}#{num_sequence}"
  end

  def yearly_sequence
    "#{year}#{type}"
  end

  def year
    Time.now.utc.strftime("%y")
  end

  def type
    ''
  end

  def lock_name
    "lock_#{self.class.to_s.underscore}_invoice_number"
  end

  def num_sequence
    last_invoice = Invoice.where("number LIKE ?", "%#{yearly_sequence}%").order('number').last
    if last_invoice.nil?
      FIRST_NUM_SEQUENCE
    else
      last_number = last_invoice.number.gsub(yearly_sequence, '').to_i
      last_number + 1
    end
  end

  def lock_manager
    @lock_manager ||= Redlock::Client.new([ENV['REDIS_URL']], {
      retry_count: 3,
      retry_delay: 1000,
      retry_jitter:  50,
      redis_timeout: 0.1
    })
  end
end