def article(article_id=None):
"""
Presents the content of an article.
"""
article = ArticleController(g.user.id).get(id=article_id)
previous_article = article.previous_article()
if previous_article is None:
previous_article = article.source.articles[0]
next_article = article.next_article()
if next_article is None:
next_article = article.source.articles[-1]
return render_template('article.html',
head_titles=[clear_string(article.title)],
article=article,
previous_article=previous_article,
next_article=next_article)
