From 073e8fbe5b573f7cf06a196b90badd28c3724ea3 Mon Sep 17 00:00:00 2001
From: Yorick Peterse <yorickpeterse@gmail.com>
Date: Thu, 16 Oct 2014 00:25:31 +0200
Subject: [PATCH] Basic boilerplate for converting CSS to XPath.

---
 lib/oga.rb                 |  1 +
 lib/oga/css/transformer.rb | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 lib/oga/css/transformer.rb

diff --git a/lib/oga.rb b/lib/oga.rb
index a8e940f..106542c 100644
--- a/lib/oga.rb
+++ b/lib/oga.rb
@@ -50,3 +50,4 @@ require_relative 'oga/xpath/evaluator'
 
 require_relative 'oga/css/lexer'
 require_relative 'oga/css/parser'
+require_relative 'oga/css/transformer'
diff --git a/lib/oga/css/transformer.rb b/lib/oga/css/transformer.rb
new file mode 100644
index 0000000..3675cc6
--- /dev/null
+++ b/lib/oga/css/transformer.rb
@@ -0,0 +1,30 @@
+module Oga
+  module CSS
+    ##
+    # Transforms an CSS AST into a corresponding XPath AST.
+    #
+    class Transformer < AST::Processor
+      def on_class(node)
+        name, test = node.to_a
+
+        unless test
+          test = s(:test, nil, '*')
+        end
+
+        predicate = s(
+          :eq,
+          s(:axis, 'attribute', s(:test, nil, 'class')),
+          s(:string, name)
+        )
+
+        return s(:axis, 'child', test.updated(nil, test.children + [predicate]))
+      end
+
+      private
+
+      def s(type, *children)
+        return AST::Node.new(type, children)
+      end
+    end # Transformer
+  end # CSS
+end # Oga