Use Diffy as DiffEngine implementation

lib/diff_engine.rb

@@ -1,21 +1,24 @@
 # This class is used to generate diffs, it will be consumed by the UI on
 # on the client the displays diffs.
 #
-# Ruby has the diff/lcs engine that can do some of the work, the devil
-#  is in the details
+# There are potential performance issues associated with diffing large amounts of completely
+# different text, see answer here for optimization if needed
+# http://meta.stackoverflow.com/questions/127497/suggested-edit-diff-shows-different-results-depending-upon-mode
 
 class DiffEngine
 
-  # generate an html friendly diff similar to the way Stack Exchange generate
-  #  html diffs
+  # generate an html friendly diff similar to the way Stack Exchange generates
+  # html diffs
   #
   #  returns: html containing decorations indicating the changes
   def self.html_diff(html_before, html_after)
+    Diffy::Diff.new(html_before, html_after).to_s(:html)
   end
 
   # same as html diff, except that it operates on markdown
   #
   # returns html containing decorated areas where diff happened
   def self.markdown_diff(markdown_before, markdown_after)
+    Diffy::Diff.new(markdown_before, markdown_after).to_s(:html)
   end
 end