create thumbnails when needed

app/models/optimized_image.rb

@@ -1,7 +1,35 @@
 class OptimizedImage < ActiveRecord::Base
   belongs_to :upload
 
-  def filename
-    "#{sha[0..2]}/#{sha[3..5]}/#{sha[6..16]}_#{width}x#{height}#{ext}"
+  def self.create_for(upload_id, path)
+    image_info = FastImage.new(path)
+    OptimizedImage.new({
+      upload_id: upload_id,
+      sha: Digest::SHA1.file(path).hexdigest,
+      ext: File.extname(path),
+      width: image_info.size[0],
+      height: image_info.size[1]
+    })
   end
+
+  def url
+    "#{Upload.base_url}/#{optimized_path}/#{filename}"
+  end
+
+  def path
+    "#{path_root}/#{optimized_path}/#{filename}"
+  end
+
+  def path_root
+    @path_root ||= "#{Rails.root}/public"
+  end
+
+  def optimized_path
+    "uploads/#{RailsMultisite::ConnectionManagement.current_db}/_optimized/#{sha[0..2]}/#{sha[3..5]}"
+  end
+
+  def filename
+    "#{sha[6..16]}_#{width}x#{height}#{ext}"
+  end
+
 end