paperclip without activerecord

image.rb

class Image
  extend ActiveModel::Naming
  extend ActiveModel::Callbacks

  include ActiveModel::Validations
  include Paperclip::Glue

  define_model_callbacks :save, only: [:after]
  define_model_callbacks :destroy, only: [:before, :after]

  attr_accessor :uuid, :attachment_file_name
  has_attached_file :attachment,
    styles: { three_dot_five_inch: "640x960>", four_inch: "640x1136>" },
    path: ":rails_root/public/system/:attachment/:uuid_partition/:style/:filename",
    url: "/system/:attachment/:uuid_partition/:style/:filename"

  def to_model
    self
  end

  def valid?()      true end
  def new_record?() true end
  def destroyed?()  true end

  def errors
    obj = Object.new
    def obj.[](key)         [] end
    def obj.full_messages() [] end
    def obj.any?()          false end
    obj
  end

  def initialize
    @uuid = UUID.new.generate.gsub('-', '')
  end

  def save
    run_callbacks :save do
    end
  end

  def destroy
    run_callbacks :destroy do
    end
  end
  
  def as_json(options={})
    {
      uuid: uuid,
      url: attachment.url(:four_inch)
    }
  end
end

images_controller.rb

class ImagesController < ApplicationController
  before_action :authenticate_user!

  def create
    image = Image.new
    image.attachment = params[:image]
    image.save
    render json: image
  end

  def show
    image = Image.new
    image.uuid = params[:id]
    image.attachment_file_name = "image_message.png"
    render json: {url: image.attachment.url(params[:style])}
  end
end

paperclip.rb

Paperclip.interpolates :uuid_partition do |attachment, style|
  attachment.instance.uuid.scan(/.{1,8}/m).join("/")
end