Birth date from personal identity number parser

birth_date_from_person_code_parser.rb

# person code format: ddmmyy-cxxxx
# where
# dd - is for birth day
# mm - is for birth month
# yy - is for birth year
# c  - is for birth century (0 - 18xx, 1 - 19xx, 2 - 20xx)
# xxxx - is a checksum generated by some secret algorithm
#
# http://www.lvportals.lv/visi/skaidrojumi/248652-personas-kods-ir-tava-identitate-sarga-to/

class BirthDateFromPersonCodeParser
  attr_reader :person_code, :year, :month, :day, :checksum, :century

  def initialize(person_code)
    @person_code = person_code.gsub '-', ''
    parse
  end

  def birth_date
    @birth_date ||= Date.new @year.to_i, @month.to_i, @day.to_i
  end

private

  def parse
    captured = /^(?<d>\d{2})(?<m>\d{2})(?<y>\d{2})(?<c>[012])(?<checksum>[0-9]{4})$/.match(person_code)
    store captured
  end

  def store(captured)
    @day = captured[:d]
    @month = captured[:m]
    @century = case captured[:c]
      when '0' then "18"
      when '1' then "19"
      when '2' then "20"
      end
    @year = "#{@century}#{captured[:y]}"
    @checksum = captured[:checksum]
  end
end

birth_date_from_person_code_parser_spec.rb

# encoding: utf-8
require 'spec_helper'

describe BirthDateFromPersonCodeParser do
  subject { BirthDateFromPersonCodeParser.new person_code }

  let(:person_code) { '23045617899' }

  context 'when given code is dash-formatted' do
    let(:person_code) { '230456-17899' }

    it 'removes dash' do
      expect( subject.person_code ).to eq '23045617899'
    end
  end

  it 'accepts code without dash' do
    expect( subject.person_code ).to eq '23045617899'
  end

  it 'correctly parses day from given person code' do
    expect( subject.day ).to eq '23'
  end

  it 'correctly parses month from given person code' do
    expect( subject.month ).to eq '04'
  end

  it 'correctly builds birth date object' do
    expect( subject.birth_date ).to eq Date.new(1956, 4, 23)
  end

  context 'when birth date is in 19 century' do
    let(:person_code) { '230415-07899' }

    it 'correctly parses year from given person code' do
      expect( subject.year ).to eq '1815'
    end

    it 'correctly builds birth date object' do
      expect( subject.birth_date ).to eq Date.new(1815, 4, 23)
    end
  end

  context 'when birth date is in 20 century' do
    let(:person_code) { '230415-17899' }

    it 'correctly parses year from given person code' do
      expect( subject.year ).to eq '1915'
    end

    it 'correctly builds birth date object' do
      expect( subject.birth_date ).to eq Date.new(1915, 4, 23)
    end
  end

  context 'when birth date is in 21 century' do
    let(:person_code) { '230415-27899' }

    it 'correctly parses year from given person code' do
      expect( subject.year ).to eq '2015'
    end

    it 'correctly builds birth date object' do
      expect( subject.birth_date ).to eq Date.new(2015, 4, 23)
    end
  end
end