import tornado.web, tornado.ioloop, tornado.template
import motor

db = motor.MotorClient().test


class NewMessageHandler(tornado.web.RequestHandler):
    def get(self):
        """Show a 'compose message' form."""
        self.write('''
        <form method="post">
            <input type="text" name="msg">
            <input type="submit">
        </form>''')

        # Method exits before the HTTP request completes, thus "asynchronous"
    @tornado.web.asynchronous
    def post(self):
        """Insert a message."""
        msg = self.get_argument('msg')
        # Async insert; callback is executed when insert completes
        self.settings['db'].messages.insert(
            {'msg': msg},
            callback=self._on_response)

    def _on_response(self, result, error):
        if error:
            raise tornado.web.HTTPError(500, error)
        else:
            self.redirect('/')


class MessagesHandler(tornado.web.RequestHandler):
    @tornado.web.asynchronous
    def get(self):
        """Display all messages"""
        self.write('<a href="/compose">Compose a message</a><br>')
        self.write('<ul>')
        ldb = self.settings['db']
        (ldb.messages.find()
        .sort([('_id', -1)])
        .to_list(self._got_messages, length=10))

    def _got_messages(self, messages, error):
        if error:
            raise tornado.web.HTTPError(500, error)
        elif messages:
            self.write(messages_template.generate(messages=messages))
        self.finish()

application = tornado.web.Application(
    [
        (r'/compose', NewMessageHandler),
        (r'/', MessagesHandler)
    ],
        db=db
    )


messages_template = tornado.template.Template('''<ul>
    {% for message in messages %}
       <li>{{ message['msg'] }}</li>
    {% end %}
    </ul>''')


print('Listening on http://localhost:8888')
application.listen(8888)
tornado.ioloop.IOLoop.instance().start()