added a new Markdown renderer (TwitteredMarkdown) which will be used for sharing to Twitter

app/helpers/markdown_helper.rb

@@ -9,4 +9,9 @@ module MarkdownHelper
     md = Redcarpet::Markdown.new(Redcarpet::Render::StripDown, MARKDOWN_OPTS)
     CGI.unescape_html(Sanitize.fragment(md.render(content), EVIL_TAGS)).strip
   end
+
+  def twitter_markdown(content)
+    md = Redcarpet::Markdown.new(TwitteredMarkdown, MARKDOWN_OPTS)
+    CGI.unescape_html(Sanitize.fragment(md.render(content), EVIL_TAGS)).strip
+  end
 end

app/models/services/twitter.rb

@@ -28,8 +28,8 @@ class Services::Twitter < Service
 
     def prepare_tweet(answer)
       # TODO: improve this.
-      question_content = strip_markdown answer.question.content
-      answer_content = strip_markdown answer.content
+      question_content = twitter_markdown answer.question.content
+      answer_content = twitter_markdown answer.content
       answer_url = show_user_answer_url(
         id: answer.id,
         username: answer.user.screen_name,

app/services/twittered_markdown.rb

@@ -0,0 +1,23 @@
+class TwitteredMarkdown < Redcarpet::Render::StripDown
+
+  def preprocess(text)
+    wrap_mentions(text)
+  end
+
+  def wrap_mentions(text)
+    text.gsub! /(^|\s)@([a-zA-Z0-9_]{1,16})/ do
+      local_user = User.find_by_screen_name($2)
+      if local_user.nil?
+        "#{$1}#{$2}"
+      else
+        service = local_user.services.where(type: "Services::Twitter").first
+        if service.nil?
+          "#{$1}#{$2}"
+        else
+          "#{$1}@#{service.nickname}"
+        end
+      end
+    end
+    text
+  end
+end