add wiki diff

app/helpers/wiki_page_versions_helper.rb

@@ -1,2 +1,51 @@
 module WikiPageVersionsHelper
+  def wiki_page_diff(thispage, otherpage)
+    pattern = Regexp.new('(?:<.+?>)|(?:\w+)|(?:[ \t]+)|(?:\r?\n)|(?:.+?)')
+
+    thisarr = thispage.body.scan(pattern)
+    otharr = otherpage.body.scan(pattern)
+
+    cbo = Diff::LCS::ContextDiffCallbacks.new
+    diffs = thisarr.diff(otharr, cbo)
+
+    escape_html = lambda {|str| str.gsub(/&/,'&amp;').gsub(/</,'&lt;').gsub(/>/,'&gt;')}
+
+    output = thisarr
+    output.each { |q| q.replace(escape_html[q]) }
+
+    diffs.reverse_each do |hunk|
+      newchange = hunk.max{|a,b| a.old_position <=> b.old_position}
+      newstart = newchange.old_position
+      oldstart = hunk.min{|a,b| a.old_position <=> b.old_position}.old_position
+
+      if newchange.action == '+'
+        output.insert(newstart, '</ins>')
+      end
+
+      hunk.reverse_each do |chg|
+        case chg.action
+        when '-'
+          oldstart = chg.old_position
+          output[chg.old_position] = '<br>' if chg.old_element.match(/^\r?\n$/)
+        when '+'
+          if chg.new_element.match(/^\r?\n$/)
+            output.insert(chg.old_position, '<br>')
+          else
+            output.insert(chg.old_position, "#{escape_html[chg.new_element]}")
+          end
+        end
+      end
+
+      if newchange.action == '+'
+        output.insert(newstart, '<ins>')
+      end
+
+      if hunk[0].action == '-'
+        output.insert((newstart == oldstart || newchange.action != '+') ? newstart+1 : newstart, '</del>')
+        output.insert(oldstart, '<del>')
+      end
+    end
+
+    output.join.gsub(/\r?\n/, '<br>').html_safe
+  end
 end