Support for the XPath translate() function.

lib/oga/xpath/evaluator.rb

@@ -1002,6 +1002,35 @@ module Oga
         return str.strip.gsub(/\s+/, ' ')
       end
 
+      ##
+      # Processes the `translate()` function call.
+      #
+      # This function takes the string of the 1st argument and replaces all
+      # characters of the 2nd argument with those specified in the 3rd argument.
+      #
+      # @example
+      #  translate("bar", "abc", "ABC") # => "BAr"
+      #
+      # @param [Oga::XML::NodeSet] context
+      # @param [Oga::XPath::Node] input
+      # @param [Oga::XPath::Node] find
+      # @param [Oga::XPath::Node] replace
+      # @return [String]
+      #
+      def on_call_translate(context, input, find, replace)
+        input_str     = on_call_string(context, input)
+        find_chars    = on_call_string(context, find).chars
+        replace_chars = on_call_string(context, replace).chars
+        replaced      = input_str
+
+        find_chars.each_with_index do |char, index|
+          replace_with = replace_chars[index] ? replace_chars[index] : ''
+          replaced     = replaced.gsub(char, replace_with)
+        end
+
+        return replaced
+      end
+
       ##
       # Processes an `(int)` node.
       #

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

@@ -0,0 +1,34 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'translate() function' do
+    before do
+      @document  = parse('<root><a>bar</a><b>abc</b><c>ABC</c></root>')
+      @evaluator = described_class.new(@document)
+    end
+
+    example 'translate a string using all string literals' do
+      @evaluator.evaluate('translate("bar", "abc", "ABC")').should == 'BAr'
+    end
+
+    example "remove characters that don't occur in the replacement string" do
+      @evaluator.evaluate('translate("-aaa-", "abc-", "ABC")').should == 'AAA'
+    end
+
+    example 'use the first character occurence in the search string' do
+      @evaluator.evaluate('translate("ab", "aba", "123")').should == '12'
+    end
+
+    example 'ignore excess characters in the replacement string' do
+      @evaluator.evaluate('translate("abc", "abc", "123456")').should == '123'
+    end
+
+    example 'translate a node set string using string literals' do
+      @evaluator.evaluate('translate(root/a, "abc", "ABC")').should == 'BAr'
+    end
+
+    example 'translate a node set string using other node set strings' do
+      @evaluator.evaluate('translate(root/a, root/b, root/c)').should == 'BAr'
+    end
+  end
+end