Configurable Image Preprocessor

app/models/alchemy/picture.rb

@@ -50,12 +50,25 @@ class Picture < BaseRecord
       raise PictureInUseError, Alchemy.t(:cannot_delete_picture_notice) % { name: name }
     end
 
+    # Image preprocessing class
+    def self.preprocessor_class
+      @_preprocessor_class ||= Preprocessor
+    end
+
+    # Set a image preprocessing class
+    #
+    #     # config/initializers/alchemy.rb
+    #     Alchemy::Picture.preprocessor_class = My::ImagePreprocessor
+    #
+    def self.preprocessor_class=(klass)
+      @_preprocessor_class = klass
+    end
+
     # Enables Dragonfly image processing
     dragonfly_accessor :image_file, app: :alchemy_pictures do
       # Preprocess after uploading the picture
-      after_assign do |p|
-        resize = Config.get(:preprocess_image_resize)
-        p.thumb!(resize) if resize.present?
+      after_assign do |image|
+        self.class.preprocessor_class.new(image).call
       end
     end
 

app/models/alchemy/picture/preprocessor.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+module Alchemy
+  class Picture < BaseRecord
+    class Preprocessor
+      def initialize(image_file)
+        @image_file = image_file
+      end
+
+      # Preprocess images after upload
+      #
+      # Define preprocessing options in the Alchemy::Config
+      #
+      #   preprocess_image_resize [String] - Downsizing example: '1000x1000>'
+      #
+      def call
+        max_image_size = Alchemy::Config.get(:preprocess_image_resize)
+        image_file.thumb!(max_image_size) if max_image_size.present?
+      end
+
+      private
+
+      attr_reader :image_file
+    end
+  end
+end