Contents

class Valvat
  module Checksum
    class GB < Base
      OLD_FORMAT_FORBIDDEN_RANGES = [(100_000..999_999), (9_490_001..9_700_000), (9_990_001..9_999_999)]
      NEW_FORMAT_FORBIDDEN_RANGES = [(1..100_000), (100_001..1_000_000)]
      GOV_NUMBER = /\A(GD[0-4]{1}\d{2})\Z/
      HEALTH_NUMBER = /\A(HA[5-9]{1}\d{2})\Z/

      def validate
        vat_number = vat.to_s_wo_country

        # government departments and health authorities, so no checksum
        return true if gov_or_health?(vat_number)
        return false if all_zero?(vat_number)

        checksum  = vat_number[7..8].to_i
        vat_base = vat_number[0..6]
        vat_base_int = vat_base.to_i
        vat_base_sum = generate_vat_base_sum(vat_base)

        old_format_remainder = (vat_base_sum + checksum).modulo(97)
        new_format_remainder = (vat_base_sum + 55 + checksum).modulo(97)

        return false if old_format_remainder == 0 &&
          OLD_FORMAT_FORBIDDEN_RANGES.any? { |range| range.include? vat_base_int }

        return false if new_format_remainder == 0 &&
          NEW_FORMAT_FORBIDDEN_RANGES.any? { |range| range.include? vat_base_int }

        old_format_remainder == 0 || new_format_remainder == 0
      end

      private

      def gov_or_health?(vat_number)
        vat_number =~ GOV_NUMBER || vat_number =~ HEALTH_NUMBER
      end

      def all_zero?(vat_number)
        vat_number =~ /\A0{9}\Z/ || vat_number =~ /\A0{12}\Z/
      end

      def generate_vat_base_sum(vat_base)
        vat_base.split('').
          map(&:to_i).
          zip([8, 7, 6, 5, 4, 3, 2]).
          map { |vat_number_digit, multiplier| vat_number_digit * multiplier }.
          inject(:+)
      end
    end
  end
end

Version data entries

2 entries across 2 versions & 1 rubygems

Version	Path
valvat-1.0.1	lib/valvat/checksum/gb.rb
valvat-1.0.0	lib/valvat/checksum/gb.rb