add service to rotate jpg attachment automatically

app/models/concerns/attachment_auto_rotate_concern.rb

@@ -0,0 +1,22 @@
+module AttachmentAutoRotateConcern
+  extend ActiveSupport::Concern
+
+  included do
+    after_create_commit :auto_rotate
+  end
+
+  private
+
+  def auto_rotate
+    return if blob.nil?
+    return if ["image/jpeg", "image/jpg"].exclude?(blob.content_type)
+
+    blob.open do |file|
+      Tempfile.create(["rotated", File.extname(file)]) do |output|
+        processed = AutoRotateService.new.process(file, output)
+        blob.upload(processed) # also update checksum & byte_size accordingly
+        blob.save!
+      end
+    end
+  end
+end

app/services/auto_rotate_service.rb

@@ -0,0 +1,30 @@
+class AutoRotateService
+  def process(file, output)
+    auto_rotate_image(file, output)
+    output
+  end
+
+  private
+
+  def auto_rotate_image(file, output)
+    image = MiniMagick::Image.new(file.to_path)
+
+    case image["%[orientation]"]
+    when 'LeftBottom'
+      rotate_image(file, output, 90)
+    when 'BottomRight'
+      rotate_image(file, output, 180)
+    when 'RightTop'
+      rotate_image(file, output, 270)
+    end
+  end
+
+  def rotate_image(file, output, degree)
+    MiniMagick::Tool::Convert.new do |convert|
+      convert << file.to_path
+      convert.rotate(degree)
+      convert.auto_orient
+      convert << output.to_path
+    end
+  end
+end

config/initializers/active_storage.rb

@@ -17,6 +17,7 @@ end
 ActiveSupport.on_load(:active_storage_attachment) do
   include AttachmentTitreIdentiteWatermarkConcern
   include AttachmentVirusScannerConcern
+  include AttachmentAutoRotateConcern
 end
 
 Rails.application.reloader.to_prepare do

spec/services/auto_rotate_service_spec.rb

@@ -0,0 +1,15 @@
+RSpec.describe AutoRotateService do
+  let(:image) { file_fixture("image-rotated.jpg") }
+  let(:auto_rotate_service) { AutoRotateService.new }
+
+  describe '#process' do
+    it 'returns a tempfile if auto_rotate succeeds' do
+      Tempfile.create do |output|
+        auto_rotate_service.process(image, output)
+        expect(MiniMagick::Image.new(image.to_path)["%[orientation]"]).to eq('LeftBottom')
+        expect(MiniMagick::Image.new(output.to_path)["%[orientation]"]).to eq('TopLeft')
+        expect(output.size).to be_between(image.size / 1.2, image.size)
+      end
+    end
+  end
+end