before_update :crop_photo

has_attached_file :photo,
                  :styles => { :original   => Proc.new { |u| u.crop_photo? ? '' : '100%x100%' },
                               :inbox      => '20x20!' },
                  :convert_options => { :original => Proc.new { |u| u.crop_photo? ? "-crop #{u.photo_crop_width}x#{u.photo_crop_height}+#{u.photo_crop_left}+#{u.photo_crop_top} +repage" : '' } }

[ :photo_crop_width, :photo_crop_height, :photo_crop_top, :photo_crop_left ].each do |attr_name|
  attr_writer attr_name
  attr_accessible attr_name
  define_method(attr_name) do
    instance_variable_get("@#{attr_name}").to_i
  end
end

def crop_photo?
  !(photo.nil? || photo.dirty? || [ photo_crop_width, photo_crop_height, photo_crop_top, photo_crop_left ].all?(&:zero?))
end

def crop_photo
  photo.reprocess! if crop_photo?
end