full_name_validator.rb

class FullNameValidator < ActiveModel::Validator

  def validate(person)

    error_string = ''
    error_string += blank_name?(person.title, person.first_name, person.last_name)
    error_string += first_name_too_long(person.first_name)
    error_string += first_name_too_short(person.first_name)
    error_string += last_name_too_long(person.last_name)
    return true if error_string == ''
    person.errors.add :full_name, I18n.t(error_string)
  end

  private

  def blank_name?(title, first, last)
    err = ''
    err += 'title_' if title.blank?
    err += 'first_' if first.blank?
    err += 'last_' if last.blank?
    error?(err, 'blank')
  end

  def first_name_too_long(first)
    err = ''
    err += '_first_too_long' if first.length > 50
    err += '_first_too_short' if first.length < 2
    error?(err, 'length')
  end

  def first_name_too_short(first)
    err = ''
    err += '_first_too_short' if first.length < 2
    error?(err, 'length')
  end

  def last_name_too_long(last)
    err = ''
    err = '_last_too_long' if last.length > 100
    error?(err, 'length')
  end

  def error?(error_str, respond_str)
    (error_str == '') ? error_str : error_str += respond_str
  end
end