Support for the XPath substring-after() function.

lib/oga/xpath/evaluator.rb

@@ -857,7 +857,7 @@ module Oga
       #
       #     substring-before("2014-08-25", "-")
       #
-      # This would return "2014" as its the first string that occurs before "-".
+      # This would return "2014" as it occurs before the first "-".
       #
       # @param [Oga::XML::NodeSet] context
       # @param [Oga::XPath::Node] haystack The string to search.
@@ -873,6 +873,30 @@ module Oga
         return sep.empty? ? sep : before
       end
 
+      ##
+      # Processes the `substring-after()` function call.
+      #
+      # This function call returns the substring of the 1st argument that occurs
+      # after the string given in the 2nd argument. For example:
+      #
+      #     substring-before("2014-08-25", "-")
+      #
+      # This would return "08-25" as it occurs after the first "-".
+      #
+      # @param [Oga::XML::NodeSet] context
+      # @param [Oga::XPath::Node] haystack The string to search.
+      # @param [Oga::XPath::Node] needle The string to search for.
+      # @return [String]
+      #
+      def on_call_substring_after(context, haystack, needle)
+        haystack_str = on_call_string(context, haystack)
+        needle_str   = on_call_string(context, needle)
+
+        before, sep, after = haystack_str.partition(needle_str)
+
+        return sep.empty? ? sep : after
+      end
+
       ##
       # Processes an `(int)` node.
       #

spec/oga/xpath/evaluator/calls/substring_after_spec.rb

@@ -0,0 +1,30 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'substring-after() function' do
+    before do
+      @document  = parse('<root><a>-</a><b>a-b-c</b></root>')
+      @evaluator = described_class.new(@document)
+    end
+
+    example 'return the substring of the 1st string after the 2nd string' do
+      @evaluator.evaluate('substring-after("a-b-c", "-")').should == 'b-c'
+    end
+
+    example 'return an empty string if the 2nd string is not present' do
+      @evaluator.evaluate('substring-after("a-b-c", "x")').should == ''
+    end
+
+    example 'return the substring of the 1st node set after the 2nd string' do
+      @evaluator.evaluate('substring-after(root/b, "-")').should == 'b-c'
+    end
+
+    example 'return the substring of the 1st node set after the 2nd node set' do
+      @evaluator.evaluate('substring-after(root/b, root/a)').should == 'b-c'
+    end
+
+    example 'return an empty string when using two empty strings' do
+      @evaluator.evaluate('substring-after("", "")').should == ''
+    end
+  end
+end