Initial, half-assed attempt at an XPath evaluator.

lib/oga.rb

@@ -31,3 +31,4 @@ require_relative 'oga/html/parser'
 require_relative 'oga/xpath/node'
 require_relative 'oga/xpath/lexer'
 require_relative 'oga/xpath/parser'
+require_relative 'oga/xpath/evaluator'

lib/oga/xpath/evaluator.rb

@@ -0,0 +1,51 @@
+module Oga
+  module XPath
+    ##
+    # The Evaluator class is used to evaluate an XPath expression in the
+    # context of a given document.
+    #
+    class Evaluator < AST::Processor
+      ##
+      # @param [Oga::XML::Document|Oga::XML::Node] document
+      #
+      def initialize(document)
+        @document = document
+        @cursor   = @document
+      end
+
+      def on_absolute(node)
+        if @cursor.is_a?(XML::Node)
+          @cursor = @cursor.root_node
+        end
+
+        return process_all(node.children)
+      end
+
+      def on_path(node)
+        test, children = *node
+
+        current = process(test)
+
+        if current
+          @cursor = current
+          current = process(children)
+        end
+
+        return current
+      end
+
+      def on_test(node)
+        nodes    = []
+        ns, name = *node
+
+        @cursor.children.each do |child|
+          if child.is_a?(XML::Element) and child.name == name and child.namespace == ns
+            nodes << child
+          end
+        end
+
+        return nodes
+      end
+    end # Evaluator
+  end # XPath
+end # Oga