Compress css in production mode

Assetfile

@@ -72,7 +72,14 @@ output 'public/styles'
 input assets.styles do
   match '**/*.{scss,sass}' do
     sass
-    concat [], 'app.css'
+    concat [], ['app.css', 'min/app.css']
+  end
+
+  if assets.production?
+    match "min/app.css" do
+      yui_css :jar_file => File.expand_path('../vendor/yuicompressor-2.4.7.jar', __FILE__)
+      concat 'app.min.css'
+    end
   end
 end
 

Gemfile

@@ -17,6 +17,7 @@ group :assets do
   gem 'compass'
   gem 'tilt'
   gem 'uglifier'
+  gem 'yui-compressor'
 end
 
 group :development, :test do

Gemfile.lock

@@ -18,6 +18,10 @@ GIT
 GEM
   remote: http://rubygems.org/
   specs:
+    POpen4 (0.1.4)
+      Platform (>= 0.4.0)
+      open4
+    Platform (0.4.0)
     backports (2.6.5)
     chunky_png (1.2.6)
     coderay (1.0.8)
@@ -62,6 +66,7 @@ GEM
     method_source (0.8.1)
     mime-types (1.19)
     multi_json (1.5.0)
+    open4 (1.3.0)
     pry (0.9.10)
       coderay (~> 1.0.5)
       method_source (~> 0.8)
@@ -116,6 +121,8 @@ GEM
       execjs (>= 0.3.0)
       multi_json (~> 1.0, >= 1.0.2)
     ya2yaml (0.31)
+    yui-compressor (0.9.6)
+      POpen4 (>= 0.1.4)
 
 PLATFORMS
   ruby
@@ -144,3 +151,4 @@ DEPENDENCIES
   sinatra-contrib
   tilt
   uglifier
+  yui-compressor