Use individual components for setting a date

person.rb

class Person < ActiveRecord::Base

  validates :name, presence: true, length: { maximum: 255 }
  validates :date_of_birth_day, presence: true, format: /\A\d{1,2}\z/
  validates :date_of_birth_month, presence: true, format: /\A\d{1,2}\z/
  validates :date_of_birth_year, presence: true, format: /\A\d{4}\z/
  validates :date_of_birth, presence: true

  validate do
    if building_date_of_birth?
      unless valid_date_of_birth_components?
        errors.add :date_of_birth, :invalid
      end
    end
  end

  before_save do
    if building_date_of_birth?
      self.date_of_birth = build_date_of_birth
    end
  end

  def date_of_birth
    if building_date_of_birth?
      if valid_date_of_birth_components?
        build_date_of_birth
      end
    else
      super
    end
  end

  def date_of_birth=(new_date)
    if building_date_of_birth?
      reset_date_of_birth_components
    end

    super
  end

  def date_of_birth_day
    if @date_of_birth_day
      @date_of_birth_day
    else
      date_of_birth && ('%02d' % date_of_birth.day)
    end
  end

  def date_of_birth_day?
    date_of_birth_day.present?
  end

  def date_of_birth_day=(new_day)
    @date_of_birth_day = new_day
  end

  def date_of_birth_month
    if @date_of_birth_month
      @date_of_birth_month
    else
      date_of_birth && ('%02d' % date_of_birth.month)
    end
  end

  def date_of_birth_month?
    date_of_birth_month.present?
  end

  def date_of_birth_month=(new_month)
    @date_of_birth_month = new_month
  end

  def date_of_birth_year
    if @date_of_birth_year
      @date_of_birth_year
    else
      date_of_birth && ('%02d' % date_of_birth.year)
    end
  end

  def date_of_birth_year?
    date_of_birth_year.present?
  end

  def date_of_birth_year=(new_year)
    @date_of_birth_year = new_year
  end

  private

  def building_date_of_birth?
    @date_of_birth_day || @date_of_birth_month || @date_of_birth_year
  end

  def build_date_of_birth
    Date.new(@date_of_birth_year.to_i, @date_of_birth_month.to_i, @date_of_birth_day.to_i)
  end

  def reset_date_of_birth_components
    @date_of_birth_day, @date_of_birth_month, @date_of_birth_year = nil, nil, nil
  end

  def valid_date_of_birth_components?
    begin
      build_date_of_birth
    rescue ArgumentError => e
      false
    end
  end

end