refactored a bit & tested thumbnails creation

app/models/optimized_image.rb

@@ -1,15 +1,39 @@
+require "digest/sha1"
+
 class OptimizedImage < ActiveRecord::Base
   belongs_to :upload
 
-  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]
-    })
+  def self.create_for(upload, width=nil, height=nil)
+    @image_sorcery_loaded ||= require "image_sorcery"
+
+    original_path = "#{Rails.root}/public#{upload.url}"
+    # create a temp file with the same extension as the original
+    temp_file = Tempfile.new(["discourse", File.extname(original_path)])
+    temp_path = temp_file.path
+
+    # do the resize when there is both dimensions
+    if width && height && ImageSorcery.new(original_path).convert(temp_path, resize: "#{width}x#{height}")
+      image_info = FastImage.new(temp_path)
+      thumbnail = OptimizedImage.new({
+        upload_id: upload.id,
+        sha: Digest::SHA1.file(temp_path).hexdigest,
+        ext: File.extname(temp_path),
+        width: image_info.size[0],
+        height: image_info.size[1]
+      })
+      # make sure the directory exists
+      FileUtils.mkdir_p Pathname.new(thumbnail.path).dirname
+      # move the temp file to the right location
+      File.open(thumbnail.path, "wb") do |f|
+        f.write temp_file.read
+      end
+    end
+
+    # close && remove temp file
+    temp_file.close
+    temp_file.unlink
+
+    thumbnail
   end
 
   def url