Rails active storage: Add the ability to rename uploaded file (supports for amazon and local)

photo.rb

# == Schema Information
#
# Table name: photos
#
#  id            :integer          not null, primary key
#  position      :integer
#  created_at    :datetime         not null
#  updated_at    :datetime         not null

class Photo < ApplicationRecord
  has_one_attached :file
  after_save_commit :set_filename, if: ->(o) { o.file.blob }
  after_update_commit :rename_remote_file, if: :position_previously_changed?

  private

  def set_filename
    file.blob.update!(key: filename, filename: filename)
  end

  def filename
    ext = self.file.filename.extension
    "#{id}-pos#{position}.#{ext}"
  end

  def rename_remote_file
    return if !file.blob

    if file.service.name == :amazon
      obj = file.service.send(:object_for, file.blob.key)
      obj.move_to(bucket: obj.bucket.name, key: filename)
    else # local
      old_path = file.service.path_for(file.blob.key)
      new_path = file.service.path_for(filename)
      FileUtils.mv(old_path, new_path)
    end
  end
end

# Samples:
# p = Photo.create!(file: { io: File.open('/my_photo.png') }, position: 1)
# puts p.file.url # ==> /1-pos1.png
# p.update!(position: 2)
# puts p.file.url # ==> /1-pos2.png

photo_spec.rb

require 'rails_helper'
RSpec.describe Photo, type: :model do
  describe 'when defining the photo name' do
    let!(:photo) { create(:photo, position: 1) }

    it 'sets the photo name when file has been added' do
      expect(photo.url).to include('_1.jpg')
    end

    it 'updates photo name when position has changed' do
      photo.update!(position: 5)
      expect(photo.url).to include('_5.jpg')
    end

    it 'updates uploaded photo name when position has changed' do
      photo.update!(position: 5)
      new_path = photo.file.service.path_for(photo.file.blob.key)
      expect(File.exist?(new_path)).to be_truthy
    end
  end
end