Danish CPR numbers: strip ssn dashes from numbers when saving, so that they are used consistently throughout the application

strip_cpr_numbers.rb

# Formatting and validation of Danish CPR number
# when saving we will throw away the dash "-" in the SSN and show it when retrieving
#
# Custom retrieval of formatted value: This is done by the method
# `formatted_cpr`. Use that in your views if you need it
#
# or in extreme cases you can override the getter method and call `formatted_cpr`
#
# Strategies for saving of unformatted value:
# 1. use either `base.after_validation` to hook into callbacks. This is a little annoying
#    for unit testing since you have to validate. But ok to use
#
# 2. use custom setter method `cpr=`, which works during typecasting of value.
#
# Both examples are included here
#
module CprFormatting
  def self.included(base)
    base.extend ClassMethods
    base.validates :cpr, format:  /\d{6}-?\d\w\w\d/

    # Strategy #1: (use only one of them)
    # base.after_validation :strip_ssn_dash
  end

  module ClassMethods
  end

  # Strategy #2: (use only one of them)
  def cpr=(val)
    self[:cpr] = val && val.delete('-')
  end

  # def strip_ssn_dash
  #   self.cpr = cpr.delete('-')
  # end

  def formatted_cpr
    if cpr.present?
      "#{cpr[0..5]}-#{cpr[6..9]}"
    else
      ''
    end
  end
end