account_number.rb

account_number.rb
¶
```
module BankOcr
  class AccountNumber
```
¶

The main interface of the AccountNumber abstraction is the error method. error receives a number_string parameter and returns a 3 characters error code or nil when there are not any errors.
```
    def self.error(number_string)
      return 'ILL' unless readable?(number_string)
      return 'ERR' unless valid_checksum?(number_string)
    end
```

The error method checks if a number_string is readable? or not

    def self.readable?(number_string)
      (number_string =~ /\?/).nil?
    end

The error method also checks if number_string has a valid_checksum? or not

    def self.valid_checksum?(number_string)
      index = 1

      number_string.reverse.chars.reduce(0) do |sum, number|
        sum += number.to_i * index
        index += 1
        sum
      end % 11 == 0
    end
  end
end