A a minimal and slightly naïve implementation at the moment, but it works!

.gitignore

@@ -3,3 +3,7 @@
 /doc/
 /pkg/
 /tmp/
+/test/dummy/tmp/
+/test/dummy/log/
+node_modules
+*.log

.travis.yml

@@ -0,0 +1,21 @@
+sudo: false
+language: ruby
+script: 'bundle exec rake'
+
+rvm:
+  - 2.2.5
+
+env:
+  - TRAVIS_NODE_VERSION='6.8.1'
+
+before_install:
+  - gem install bundler -v 1.12.5
+  - rm -rf ~/.nvm && git clone https://github.com/creationix/nvm.git ~/.nvm && (cd ~/.nvm && git checkout `git describe --abbrev=0 --tags`) && source ~/.nvm/nvm.sh && nvm install $TRAVIS_NODE_VERSION
+  - npm install
+
+notifications:
+  email:
+    recipients:
+      - mail@tomascelizna.com
+    on_failure: change
+    on_success: never

Gemfile

@@ -1,4 +1,6 @@
-source "https://rubygems.org"
+source 'https://rubygems.org'
 
 # Specify your gem's dependencies in cssm-rails.gemspec
 gemspec
+
+gem 'rb-readline'

README.md

@@ -1,5 +1,12 @@
 # CSS Modules for Rails
 
+[![Build Status](https://travis-ci.org/tomasc/cssm-rails.svg)](https://travis-ci.org/tomasc/cssm-rails) [![Gem Version](https://badge.fury.io/rb/cssm-rails.svg)](http://badge.fury.io/rb/cssm-rails)
+
+A Rails (Sprockets) wrapper on CSS Modules (respective the [CSS Module Loader Core](https://github.com/css-modules/css-modules-loader-core)).
+It is a minimal and slightly naïve implementation at the moment (for example calling `node` command directly via command-line). Pull requests are more than welcome.
+
+**A current drawback of an implementation of CSS Modules in Rails is, that it makes views dependent on stylesheets. Currently there is no way how to include digests of relevant stylesheet files with Rails partial digests. This in turn renders this solution unusable in connection with so called russian-doll-caching, since changes to stylesheet assets won't bust the view cache. Ideas and solutions welcome.**
+
 ## Installation
 
 Add this line to your application's Gemfile:
@@ -10,27 +17,90 @@ gem 'cssm-rails'
 
 And then execute:
 
-    $ bundle
+```sh
+$ bundle
+```
 
 Or install it yourself as:
 
-    $ gem install cssm-rails
+```sh
+$ gem install cssm-rails
+```
+
+## Requirements
+
+This gem requires Node to be installed.
 
 ## Usage
 
-Put foo.cssm in your app/assets/stylesheets directory with `.bar { color: red; }`. Use `<div class="<%= cssm "foo:bar" %>">` in your views. `//= require cssm` in then `CSSM.foo.bar` to use from javascript.
+Files with `*.cssm`, `*.sassm`, `*.scssm` will be processed for CSS modules.
+Files with `*.css`, `*.sass`, `*.scss` extensions will remain unchanged.
+
+```css
+/* common.cssm */
+.bg { /* this class will be transformed to `.common_bg_HASH` */ };
+```
+
+```css
+/* event.cssm */
+.title {
+  composes: bg from './common.cssm';
+  /* this class will be transformed to `.event_title_HASH`,
+  the outcome of the `cssm` helper will then be `event_title_HASH common_bg_HASH`
+  */
+}
+```
+
+### Helpers
+
+The `cssm` helper outputs css module classes:
+
+```ruby
+cssm(file_name, class_name)
+```
+
+For example:
+
+```ruby
+cssm('event', 'title') # => 'event_title_HASH common_bg_HASH'
+```
+
+The `cssms` outputs class selector:
+
+```ruby
+cssms('event', 'title') # => '.event_title_HASH.common_bg_HASH'
+```
+
+These are helpful to generate module classes in views:
+
+```ruby
+<p class="<%= cssm 'event', 'title' %>"> # => <p class="event_title_HASH common_bg_HASH">
+  event title
+</p>
+```
+
+And selectors in JS:
+
+```js
+$("<%= cssms 'event', 'title' %>"); // => $('.event_title_HASH.common_bg_HASH')
+```
 
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. You can also run `bin/console` for an interactive prompt that will allow you to experiment.
 
 To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).
 
+### Rebuilding CSS Modules JS
+
+```sh
+bundle exec rake vendor_build
+```
+
 ## Contributing
 
 Bug reports and pull requests are welcome on GitHub at https://github.com/css-modules/cssm-rails.
 
 ## License
 
 The gem is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).
-

Rakefile

@@ -1 +1,23 @@
-require "bundler/gem_tasks"
+require 'bundler/gem_tasks'
+require 'rake/testtask'
+
+Rake::TestTask.new(:test) do |t|
+  t.libs << 'test'
+  t.libs << 'lib'
+  t.test_files = FileList['test/**/*_test.rb']
+end
+
+task default: :test
+
+desc 'rebuild the vendored postcss-modules'
+task :vendor_build do
+  `cd vendor/src && npm install`
+  `cd vendor/src && npm run bundle`
+
+  # re-enable the fs module (which would be removed by browserify if uncommented)
+  bundle = File.join(__dir__, 'vendor/bundle.js')
+  content = File.read(bundle).gsub("// var fs = require('fs');", "var fs = require('fs');")
+  File.open(bundle, 'w+') do |output_file|
+    output_file.write(content)
+  end
+end

cssm-rails.gemspec

@@ -4,29 +4,29 @@ $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 require 'cssm/rails/version'
 
 Gem::Specification.new do |spec|
-  spec.name          = "cssm-rails"
+  spec.name          = 'cssm-rails'
   spec.version       = CSSM::Rails::VERSION
-  spec.authors       = ["Samuel Cochran"]
-  spec.email         = ["sj26@sj26.com"]
+  spec.authors       = ['Tomas Celizna']
+  spec.email         = ['mail@tomascelizna.com']
 
-  spec.summary       = %q{CSS Modules for Rails}
-  spec.description   = %q{A CSS Module is a CSS file in which all class names and animation names are scoped locally by default. All URLs (url(...)) and @imports are in module request format (./xxx and ../xxx means relative, xxx and xxx/yyy means in modules folder, i. e. in node_modules).}
-  spec.homepage      = "https://github.com/css-modules/cssm-rails"
-  spec.license       = "MIT"
-
-  # Prevent pushing this gem to RubyGems.org by setting 'allowed_push_host', or
-  # delete this section to allow pushing this gem to any host.
-  if spec.respond_to?(:metadata)
-    spec.metadata['allowed_push_host'] = "TODO: Set to 'http://mygemserver.com'"
-  else
-    raise "RubyGems 2.0 or newer is required to protect against public gem pushes."
-  end
+  spec.summary       = 'CSS Modules for Rails'
+  spec.description   = 'A CSS Module is a CSS file in which class names and animation names are scoped locally.'
+  spec.homepage      = 'https://github.com/css-modules/cssm-rails'
+  spec.license       = 'MIT'
 
   spec.files         = `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
-  spec.bindir        = "exe"
+  spec.bindir        = 'exe'
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
-  spec.require_paths = ["lib"]
+  spec.require_paths = ['lib']
+
+  spec.add_dependency 'rails'
+  spec.add_dependency 'sassc'
+  spec.add_dependency 'sassc-rails'
+  spec.add_dependency 'sprockets'
 
-  spec.add_development_dependency "bundler", "~> 1.10"
-  spec.add_development_dependency "rake", "~> 10.0"
+  spec.add_development_dependency 'bundler', '~> 1.10'
+  spec.add_development_dependency 'minitest', '~> 5.0'
+  spec.add_development_dependency 'minitest-rails'
+  spec.add_development_dependency 'minitest-rails-capybara'
+  spec.add_development_dependency 'rake', '~> 10.0'
 end

lib/cssm.rb

@@ -1,2 +1 @@
-module CSSM
-end
+require_relative 'rails/rails'

lib/cssm/rails.rb

@@ -1,9 +1,34 @@
-require "cssm/rails/version"
-
-require "cssm"
-
 module CSSM
   module Rails
-    # Your code goes here...
+    ROOT_PATH = __dir__
+
+    autoload :Sprockets, 'cssm/rails/sprockets'
+
+    def self.process(css, opts = {})
+      params = {}
+      processor(params).process(css, opts)
+    end
+
+    def self.install(assets, params = {})
+      Sprockets.register_processor(processor(params))
+      Sprockets.install(assets)
+    end
+
+    def self.uninstall(assets)
+      Sprockets.uninstall(assets)
+    end
+
+    def self.processor(params = {})
+      Processor.new(params)
+    end
   end
 end
+
+require_relative 'rails/asset'
+require_relative 'rails/processor'
+require_relative 'rails/result'
+require_relative 'rails/view_helper'
+
+require_relative 'rails/railtie' if defined?(Rails)
+
+require_relative 'rails/version'

lib/cssm/rails/asset.rb

@@ -0,0 +1,33 @@
+module CSSM
+  module Rails
+    class Asset < Struct.new(:name, :options)
+      def initialize(name, options = {})
+        super(name, options)
+      end
+
+      def path
+        @path ||= paths.flat_map do |path|
+          Dir.glob("#{path}/**/#{name}.{#{extensions.join(',')}}")
+        end.first
+      end
+
+      def css
+        @css ||= File.read(path)
+      end
+
+      def digest
+        @digest ||= Digest::MD5.hexdigest(css)
+      end
+
+      private
+
+      def extensions
+        options.fetch :extensions, %w(cssm sassm scssm)
+      end
+
+      def paths
+        @paths ||= ::Rails.application.config.assets.paths
+      end
+    end
+  end
+end

lib/cssm/rails/processor.rb

@@ -0,0 +1,23 @@
+module CSSM
+  module Rails
+    class Processor < Struct.new(:params)
+      BUNDLE_JS_PATH = File.join(ROOT_PATH, '../..', 'vendor/bundle.js')
+
+      def initialize(params = {})
+        super(params)
+      end
+
+      def process(css, opts = {})
+        filename = opts.fetch(:from, nil)
+
+        bundle_js_args = Shellwords.escape(BUNDLE_JS_PATH)
+        css_arg = Shellwords.escape(css)
+        filename_arg = Shellwords.escape(filename.to_s)
+
+        result = JSON.parse `node #{bundle_js_args} #{css_arg} #{filename_arg}`
+
+        Result.new(result['injectableSource'], result['exportTokens'])
+      end
+    end
+  end
+end

lib/cssm/rails/railtie.rb

@@ -0,0 +1,52 @@
+require 'sassc-rails'
+require 'sprockets/railtie'
+
+begin
+  module CSSM
+    module Rails
+      class Railtie < ::Rails::Railtie
+        config.cssm = ActiveSupport::OrderedOptions.new
+
+        if config.respond_to?(:annotations)
+          config.annotations.register_extensions("scssm", "sassm") { |annotation| /\/\/\s*(#{annotation}):?\s*(.*)$/ }
+        end
+
+        initializer :setup_sass, group: :all do |app|
+          config.assets.configure do |env|
+            if env.respond_to?(:register_transformer)
+              env.register_transformer 'text/sass-modules', 'text/css', SassC::Rails::SassTemplate.new
+              env.register_transformer 'text/scss-modules', 'text/css', SassC::Rails::ScssTemplate.new
+            end
+
+            if env.respond_to?(:register_engine)
+              [
+                ['.sassm', SassC::Rails::SassTemplate],
+                ['.scssm', SassC::Rails::ScssTemplate]
+              ].each do |engine|
+                engine << { silence_deprecation: true } if ::Sprockets::VERSION.start_with?("3")
+                env.register_engine(*engine)
+              end
+            end
+          end
+        end
+
+        initializer :cssm_rails_view_helpers do
+          ActionView::Base.send :include, CSSM::Rails::ViewHelper
+        end
+
+        if config.respond_to?(:assets) && !config.assets.nil?
+          config.assets.configure do |env|
+            CSSM::Rails.install(env, {})
+          end
+        else
+          initializer :setup_cssm_rails, group: :all do |app|
+            if defined? app.assets && !app.assets.nil?
+              CSSM::Rails.install(app.assets, {})
+            end
+          end
+        end
+      end
+    end
+  rescue LoadError
+  end
+end

lib/cssm/rails/result.rb

@@ -0,0 +1,13 @@
+module CSSM
+  module Rails
+    class Result < Struct.new(:injectable_source, :export_tokens)
+      def initialize(injectable_source, export_tokens)
+        super(injectable_source, export_tokens)
+      end
+
+      def to_s
+        injectable_source
+      end
+    end
+  end
+end