Add methods to allow generation of critical CSS for a specific route and to allow removal of specific routes from the CSS cache.

Author: taranda

README.md

@@ -8,13 +8,16 @@ This gem assumes that you'll load the rest of the CSS asyncronously. At the mome
 
 This gem uses [PhantomJS](https://github.com/colszowka/phantomjs-gem) and [Penthouse](https://github.com/pocketjoso/penthouse) to generate the critical CSS.
 
+## Update
+
+Version 0.3.0 is not compatible with previous versions.  Please read the Upgrading from Previous Versions section below for more information.
 
 ## Installation
 
 Add `critical-path-css-rails` to your Gemfile:
 
 ```
-gem 'critical-path-css-rails', '~> 0.2.0'
+gem 'critical-path-css-rails', '~> 0.3.0'
 ```
 
 Download and install by running:
@@ -65,20 +68,56 @@ To load the generated critical CSS into your layout, in the head tag, insert:
 </style>
 ```
 
-A simple example using loadcss-rails looks like:
+A simple example using [loadcss-rails](https://github.com/michael-misshore/loadcss-rails) looks like:
 
 ```HTML+ERB
 <style>
-    <%= CriticalPathCss.fetch(request.path) %>
+  <%= CriticalPathCss.fetch(request.path) %>
 </style>
-<script>
-    loadCSS("<%= stylesheet_path('application') %>");
-</script>
+<%= tag :link, as: 'style', href: stylesheet_path('application'), onload: raw("this.rel='stylesheet'"), rel: 'preload' %>
 <noscript>
-    <%= stylesheet_link_tag 'application', media: 'all', 'data-turbolinks-track' => true %>
+  <%= stylesheet_link_tag 'application', media: 'all', 'data-turbolinks-track' => true %>
 </noscript>
 ```
 
+### Route-level Control of CSS Generation and Removal
+
+CriticalPathCss exposes some methods to give the user more control over the generation of Critical CSS and managment of the CSS cache:
+
+``` ruby
+CriticalPathCss.generate route         # Generates the critical path CSS for the given route (relative path)
+
+CriticalPathCss.generate_all           # Generates critical CSS for all routes in critical_path_css.yml
+
+CriticalPathCss.clear route            # Removes the CSS for the given route from the cache
+
+CriticalPathCss.clear_matched routes   # Removes the CSS for the matched routes from the cache
+
+CriticalPathCss.clear_all              # Clears all CSS from the cache
+```
+
+In addition to the `critical_path_css:generate` rake task described above, you also have access to task which clears the CSS cache:
+
+```
+rake critical_path_css:clear_all
+```
+
+Careful use of these methods allows the developer to generate critical path CSS dynamically within the app.  The user should strongly consider using a [background job](http://edgeguides.rubyonrails.org/active_job_basics.html) when generating CSS in order to avoid tying up a rails thread.  The `generate` method will send a GET request to your server which could cause infinite recursion if the developer is not careful.
+
+A user can use these methods to [dynamically generate critical path CSS](https://gist.github.com/taranda/1597e97ccf24c978b59aef9249666c77) without using the `rake critical_path_css:generate` rake task and without hardcoding the application's routes into `config/critical_path_css.yml`.  See [this Gist](https://gist.github.com/taranda/1597e97ccf24c978b59aef9249666c77) for an example of such an implementation.
+
+## Upgrading from Previous Versions
+
+The latest version of Critcal Path CSS Rails changes the functionality of the `generate` method.  In past versions,
+`generate` would produce CSS for all of the routes listed in `config/critical_path_css.yml`.  This functionality has been replaced by the `generate_all` method, and `generate` will only produce CSS for one route.
+
+Developers upgrading from versions prior to 0.3.0 will need to replace `CriticalPathCss:generate` with `CriticalPathCss:generate_all` throughout their codebase.  One file that will need updating is `lib/tasks/critical_path_css.rake`.  Users can upgrade this file automatically by running:
+
+``` prompt
+rails generate critical_path_css:install
+```
+
+Answer 'Y' when prompted to overwrite `critical_path_css.rake`.  However, overwriting `critical_path_css.yml` is not necessary and not recommended.
 
 ## Versions
 

lib/critical-path-css-rails.rb

@@ -3,12 +3,28 @@ module CriticalPathCss
 
   CACHE_NAMESPACE = 'critical-path-css'
 
-  def self.generate
+  def self.generate(route)
+      Rails.cache.write(route, CssFetcher.new.fetch_route(route), namespace: CACHE_NAMESPACE)
+  end
+
+  def self.generate_all
     CssFetcher.new.fetch.each do |route, css|
       Rails.cache.write(route, css, namespace: CACHE_NAMESPACE)
     end
   end
 
+  def self.clear(route)
+    Rails.cache.delete(route, namespace: CACHE_NAMESPACE)
+  end
+
+  def self.clear_matched(routes)
+    Rails.cache.delete_matched(routes,namespace: CACHE_NAMESPACE)
+  end
+
+  def self.clear_all
+    self.clear_matched('*')
+  end
+
   def self.fetch(route)
     Rails.cache.read(route, namespace: CACHE_NAMESPACE) || ''
   end

lib/critical_path_css/css_fetcher.rb

@@ -13,7 +13,11 @@ def fetch
       @config.routes.map { |route| [route, css_for_route(route)] }.to_h
     end
 
-    private
+    def fetch_route(route)
+      css_for_route route
+    end
+
+  protected
 
     def css_for_route(route)
       Phantomjs.run(PENTHOUSE_PATH, @config.base_url + route, @config.css_path)

lib/critical_path_css/rails/version.rb

@@ -1,6 +1,6 @@
 module CriticalPathCSS
   module Rails
-    VERSION = '0.2.3'
+    VERSION = '0.3.0'
     PENTHOUSE_VERSION = '0.3.4'
   end
 end

lib/tasks/critical_path_css.rake

@@ -3,7 +3,11 @@ require 'critical-path-css-rails'
 namespace :critical_path_css do
   desc 'Generate critical CSS for the routes defined'
   task generate: :environment do
-    CriticalPathCss.generate
+    CriticalPathCss.generate_all
+  end
+  desc 'Clear all critical CSS from the cache'
+  task clear_all: :environment do
+  	CriticalPathCss.clear_all
   end
 end