# config/initializers/shrine.rb
require "shrine"
require "shrine/storage/file_system"

Shrine.storages = {
  cache: Shrine::Storage::FileSystem.new("public", prefix: "uploads/cache"), # temporary
  store: Shrine::Storage::FileSystem.new("public", prefix: "uploads"),       # permanent
}

Shrine.plugin :activerecord
Shrine.plugin :backgrounding
Shrine.plugin :pretty_location

Shrine::Attacher.promote_block do
  PromoteFileJob.perform_later(self.class.name, record.class.name, record.id, name, file_data)
end

# app/jobs/promote_file_job.rb
class PromoteFileJob < ApplicationJob
  def perform(attacher_klass_name, record_klass, record_id, name, file)
    attacher_klass = Object.const_get(attacher_klass_name)
    model = Object.const_get(record_klass).find(record_id)

    attacher = attacher_klass.retrieve(model:, name:, file:)
    attacher.atomic_promote
  rescue Shrine::AttachmentChanged, ActiveRecord::RecordNotFound
    # attachment has changed or record has been deleted, nothing to do
  end
end

# app/uploaders/uploader.rb
class Uploader < Shrine
end

# db/migrate/20250204162317_create_posts.rb
class CreatePosts < ActiveRecord::Migration[8.0]
  def change
    create_table :posts do |t|
      t.text :image_data

      t.timestamps
    end
  end
end

# app/models/post.rb
class Post < ApplicationRecord
  include Uploader[:image]
end

# spec/factories/posts.rb
FactoryBot.define do
  factory :post do
    image { File.open("spec/fixtures/test.png") }
  end
end

# spec/models/post_spec.rb
require 'rails_helper'

RSpec.describe Post, type: :model do
  specify do
    post = FactoryBot.create(:post)
    expect(post.image.url).to include("post/#{post.id}/image")
  end
end