Add gh-pages docs publish task

Adapted from
https://github.com/ruby-grape/grape/blob/864568d903e283d91da46fdebceb2605236ab55e/Rakefile

Author: bf4

Rakefile

@@ -12,11 +12,7 @@ Bundler::GemHelper.install_tasks
 
 require 'yard'
 
-namespace :yard do
-  YARD::Rake::YardocTask.new(:doc) do |t|
-    t.stats_options = ['--list-undoc']
-  end
-
+namespace :doc do
   desc 'start a gem server'
   task :server do
     sh 'bundle exec yard server --gems'
@@ -28,6 +24,63 @@ namespace :yard do
     sh "bundle exec yard graph --protected --full --dependencies > #{output_file}"
     puts 'open doc/erd.dot if you have graphviz installed'
   end
+
+  DOC_FILES = ['lib/**/*.rb', 'README.md'].freeze
+  DOC_REF = `git log --pretty=format:'%h' -1`.chomp
+  DOC_REMOTE = "[email protected]:rails-api/active_model_serializers.git"
+  DOC_VERSION = ActiveModel::Serializer::VERSION
+  DOC_PATH = '../ams.doc'
+  DOC_DIR  = File.dirname(__FILE__) + '/../ams.doc'
+
+  YARD::Rake::YardocTask.new(:doc) do |t|
+    t.stats_options = ['--list-undoc']
+    t.files = DOC_FILES
+  end
+
+  YARD::Rake::YardocTask.new(:pages) do |t|
+    t.files   = DOC_FILES
+    t.options = ['-o', DOC_PATH]
+  end
+
+  namespace :pages do
+    task :clean do
+      Dir.chdir(DOC_DIR) do
+        next unless File.directory?('.git')
+        sh 'git rm -rf . || echo $!'
+      end
+    end
+
+    desc 'Check out gh-pages.'
+    task :checkout do
+      unless Dir.exist?(DOC_DIR)
+        Dir.mkdir(DOC_DIR)
+        Dir.chdir(DOC_DIR) do
+          sh 'git init'
+          sh "git remote add origin #{DOC_REMOTE}"
+          sh 'git pull'
+          sh 'git checkout gh-pages' || begin
+            sh 'git checkout --orphan gh-pages'
+            sh 'git rm -rf .'
+            sh 'echo "Page" > index.html'
+            sh 'git add index.html'
+            sh 'git commit -a -m "First pages commit"'
+            sh 'git push origin gh-pages'
+          end
+        end
+      end
+    end
+
+    desc 'Generate and publish YARD docs to GitHub pages.'
+    task publish: ['doc:pages:checkout', 'doc:pages:clean', 'doc:pages'] do
+      Dir.chdir(DOC_DIR) do
+        sh 'git checkout gh-pages'
+        sh 'git add .'
+        sh 'git add -u'
+        sh "git commit -m 'Generating docs for version #{DOC_VERSION} at ref #{DOC_REF}.'"
+        sh 'git push origin gh-pages'
+      end
+    end
+  end
 end
 
 begin