From b9a1f914bd9eb8f128955facff74a0e3e2f9247d Mon Sep 17 00:00:00 2001
From: Yorick Peterse <yorickpeterse@gmail.com>
Date: Thu, 2 Oct 2014 23:31:58 +0200
Subject: [PATCH] Basic CSS parser boilerplate.

This currently only parses single node tests (e.g. just "foo").
---
 .gitignore           |  1 +
 lib/oga.rb           |  1 +
 lib/oga/css/parser.y | 84 ++++++++++++++++++++++++++++++++++++++++++++
 task/parser.rake     |  6 +++-
 4 files changed, 91 insertions(+), 1 deletion(-)
 create mode 100644 lib/oga/css/parser.y

diff --git a/.gitignore b/.gitignore
index d14b3c1..c83d889 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,6 +7,7 @@ lib/oga/xml/parser.rb
 lib/oga/xpath/lexer.rb
 lib/oga/xpath/parser.rb
 lib/oga/css/lexer.rb
+lib/oga/css/parser.rb
 
 lib/liboga.*
 
diff --git a/lib/oga.rb b/lib/oga.rb
index 0549640..a8e940f 100644
--- a/lib/oga.rb
+++ b/lib/oga.rb
@@ -49,3 +49,4 @@ require_relative 'oga/xpath/parser'
 require_relative 'oga/xpath/evaluator'
 
 require_relative 'oga/css/lexer'
+require_relative 'oga/css/parser'
diff --git a/lib/oga/css/parser.y b/lib/oga/css/parser.y
new file mode 100644
index 0000000..a663097
--- /dev/null
+++ b/lib/oga/css/parser.y
@@ -0,0 +1,84 @@
+##
+# AST parser for CSS expressions.
+#
+class Oga::CSS::Parser
+
+options no_result_var
+
+rule
+  css
+    : selectors  { val[0] }
+    | /* none */ { nil }
+    ;
+
+  selectors
+    : selectors selector { val[0] << val[1] }
+    | selector           { val[0] }
+    ;
+
+  selector
+    : node_test
+    ;
+
+  node_test
+    : node_name { s(:test, *val[0]) }
+    ;
+
+  node_name
+    # foo
+    : T_IDENT { [nil, val[0]] }
+
+    # ns|foo
+    | T_IDENT T_PIPE T_IDENT { [val[0], val[2]] }
+
+    # |foo
+    | T_PIPE T_IDENT { [nil, val[1]] }
+    ;
+end
+
+---- inner
+  ##
+  # @param [String] data The input to parse.
+  #
+  def initialize(data)
+    @lexer = Lexer.new(data)
+  end
+
+  ##
+  # @param [Symbol] type
+  # @param [Array] children
+  # @return [AST::Node]
+  #
+  def s(type, *children)
+    return AST::Node.new(type, children)
+  end
+
+  ##
+  # Yields the next token from the lexer.
+  #
+  # @yieldparam [Array]
+  #
+  def yield_next_token
+    @lexer.advance do |*args|
+      yield args
+    end
+
+    yield [false, false]
+  end
+
+  ##
+  # Parses the input and returns the corresponding AST.
+  #
+  # @example
+  #  parser = Oga::CSS::Parser.new('foo.bar')
+  #  ast    = parser.parse
+  #
+  # @return [AST::Node]
+  #
+  def parse
+    ast = yyparse(self, :yield_next_token)
+
+    return ast
+  end
+
+# vim: set ft=racc:
diff --git a/task/parser.rake b/task/parser.rake
index 562a025..553d599 100644
--- a/task/parser.rake
+++ b/task/parser.rake
@@ -3,4 +3,8 @@ rule '.rb' => '.y' do |task|
 end
 
 desc 'Generates the parser'
-task :parser => ['lib/oga/xml/parser.rb', 'lib/oga/xpath/parser.rb']
+task :parser => [
+  'lib/oga/xml/parser.rb',
+  'lib/oga/xpath/parser.rb',
+  'lib/oga/css/parser.rb'
+]