frontend: add rake tasks, improve performance in 'watch' mode

twenty-frontend/Gemfile

@@ -6,3 +6,11 @@ gem "nanoc-live", "~> 1.0"
 gem "nanoc-webpack.rb", "~> 0.5"
 gem "sass", "~> 3.7"
 gem "rainpress", "~> 1.0"
+
+require 'rbconfig'
+case RbConfig::CONFIG['target_os']
+when /(?i-mx:bsd|dragonfly)/
+  gem 'rb-kqueue', '>= 0.2'
+else
+   # Poll
+end

twenty-frontend/Gemfile.lock

@@ -94,6 +94,8 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
+    rb-kqueue (0.2.8)
+      ffi (>= 0.5.0)
     rbtree (0.4.6)
     ryo.rb (0.4.5)
     sass (3.7.4)
@@ -126,6 +128,7 @@ DEPENDENCIES
   nanoc-webpack.rb (~> 0.5)
   rainpress (~> 1.0)
   rake (~> 13.0)
+  rb-kqueue (>= 0.2)
   sass (~> 3.7)
   twenty-frontend!
 

twenty-frontend/Rakefile.rb

@@ -1,4 +1,5 @@
 require "bundler/setup"
+load 'tasks/nanoc.rake'
 namespace :schema do
   desc "Generate src/js/types/schema.ts"
   task :regen do

twenty-frontend/tasks/nanoc.rake

@@ -0,0 +1,17 @@
+namespace :nanoc do
+  desc "Produce the build/ directory"
+  task :build do
+    sh "nanoc co"
+  end
+
+  desc "Produce the build/ directory on-demand"
+  task watch: ['nanoc:build'] do
+    require "listen"
+    path = File.join(Dir.getwd, "src")
+    Listen.to(path) { sh "rake nanoc:build" }.start
+    sleep
+  rescue Interrupt
+    warn "SIGINT: exit"
+    exit
+  end
+end