class NHSNumberValidator

# File app/validators/nhs_number_validator.rb, line 6
def validate_each(record, attribute, value)
  if value.blank?
    record.errors.add(attribute, :blank) unless options[:allow_blank]
  elsif value.nil?
    record.errors.add(attribute, :blank) unless options[:allow_nil]
  elsif value.length != 10
    record.errors.add(
      attribute,
      options[:message] || :wrong_length,
      count: 10
    )
  else
    # https://archive.datadictionary.nhs.uk/DD%20Release%20May%202024/attributes/nhs_number.html
    digits = value.chars.map { DIGITS.include?(it) ? it.to_i : nil }

    if digits.any?(&:nil?)
      record.errors.add(attribute, options[:message] || :invalid)
      return
    end

    digits_multiplied_by_weighting_factor =
      digits
        .slice(0, 9)
        .each_with_index
        .map { |digit, index| (11 - (index + 1)) * digit }

    digits_sum_remainder = digits_multiplied_by_weighting_factor.sum % 11

    check_digit = (digits_sum_remainder.zero? ? 0 : 11 - digits_sum_remainder)

    if check_digit > 9 || digits.last != check_digit
      record.errors.add(attribute, options[:message] || :invalid)
    end
  end
end