Ensure tweets fit twitter's length limit

app/models/services/twitter.rb

@@ -27,16 +27,30 @@ class Services::Twitter < Service
     end
 
     def prepare_tweet(answer)
-      # TODO: improve this.
       question_content = twitter_markdown answer.question.content.gsub(/\@(\w+)/, '\1')
+      original_question_length = question_content.length
       answer_content = twitter_markdown answer.content
+      original_answer_length = answer_content.length
       answer_url = show_user_answer_url(
         id: answer.id,
         username: answer.user.screen_name,
         host: APP_CONFIG['hostname'],
         protocol: (APP_CONFIG['https'] ? :https : :http)
       )
-      "#{question_content[0..122]}#{'…' if question_content.length > 123}" \
-        " — #{answer_content[0..123]}#{'…' if answer_content.length > 124} #{answer_url}"
+
+      parsed_tweet = { :valid => false }
+      tweet_text = ""
+
+      until parsed_tweet[:valid]
+        tweet_text = "#{question_content[0..122]}#{'…' if original_question_length > question_content.length}" \
+          " — #{answer_content[0..123]}#{'…' if original_answer_length > answer_content.length} #{answer_url}"
+
+        parsed_tweet = Twitter::TwitterText::Validation::parse_tweet(tweet_text)
+
+        question_content = question_content[0..-2]
+        answer_content = answer_content[0..-2]
+      end
+
+      tweet_text
     end
 end