taxid_validator.rb

# frozen_string_literal: true

class TaxidValidator < ActiveModel::EachValidator
  VALID_FORMATS = {
    nif: /^(\d{8})([A-Z])$/,
    nie: /^[XYZ]\d{7,8}[A-Z]$/,
  }.freeze

  CONTROL_DIGIT_TABLE = %w[T R W A G M Y F P D X B N J Z S Q V H L C K E].freeze
  CONTROL_DIGIT_NIE_MAPPING = {
    X: 0, Y: 1, Z: 2,
  }.freeze

  def validate_each(record, attribute, value)
    provided_taxid = value.dup
    record.errors.add(attribute, :invalid_taxid_format) unless valid_format(provided_taxid)
    record.errors.add(attribute, :invalid_taxid_control_digit) unless valid_control_digit(provided_taxid)
  end

  private def valid_format(taxid)
    VALID_FORMATS[:nif] =~ taxid || VALID_FORMATS[:nie] =~ taxid
  end

  private def valid_control_digit(taxid)
    provided_control_digit = taxid.slice!(-1)
    if VALID_FORMATS[:nie] =~ taxid
      replacement = CONTROL_DIGIT_NIE_MAPPING[taxid[0].to_sym]
      taxid = "#{replacement}#{taxid[1..-1]}"
    end
    provided_control_digit == CONTROL_DIGIT_TABLE[taxid.to_i % 23]
  end
end