class ThingsResource:
    def on_get(self, req, resp):
        """Handles GET requests"""
        resp.status = falcon.HTTP_200
        resp.body = 'Hello world!'

# falcon.API instances are callable WSGI apps
wsgi_app = api = falcon.API()

# Resources are represented by long-lived class instances
things = ThingsResource()

# things will handle all requests to the '/things' URL path
api.add_route('/things', things)

import json
import logging

import falcon


class StorageEngine:
    pass


class StorageError(Exception):
    pass


def token_is_valid(token, user_id):
    return True  # Suuuuuure it's valid...


def auth(req, resp, params):
    # Alternatively, do this in middleware
    token = req.get_header('X-Auth-Token')

    if token is None:
        raise falcon.HTTPUnauthorized('Auth token required',
                                      'Please provide an auth token '
                                      'as part of the request',
                                      'http://docs.example.com/auth')

    if not token_is_valid(token, params['user_id']):
        raise falcon.HTTPUnauthorized('Authentication required',
                                      'The provided auth token is '
                                      'not valid. Please request a '
                                      'new token and try again.',
                                      'http://docs.example.com/auth')


def check_media_type(req, resp, params):
    if not req.client_accepts_json():
        raise falcon.HTTPUnsupportedMediaType(
            'Media Type not Supported',
            'This API only supports the JSON media type.',
            'http://docs.examples.com/api/json')


class ThingsResource:

    def __init__(self, db):
        self.db = db
        self.logger = logging.getLogger('thingsapi.' + __name__)

    def on_get(self, req, resp, user_id):
        marker = req.get_param('marker', default='')
        limit = req.get_param('limit', default=50)

        try:
            result = self.db.get_things(marker, limit)
        except Exception as ex:
            self.logger.error(ex)

            description = ('Aliens have attacked our base! We will '
                           'be back as soon as we fight them off. '
                           'We appreciate your patience.')

            raise falcon.HTTPServiceUnavailable('Service Outage', description)

        resp.set_header('X-Powered-By', 'Donuts')
        resp.status = falcon.HTTP_200
        resp.body = json.dumps(result)

    def on_post(self, req, resp, user_id):
        try:
            raw_json = req.stream.read()
        except Exception:
            raise falcon.HTTPError(falcon.HTTP_748,
                                   'Read Error',
                                   'Could not read the request body. Must be '
                                   'them ponies again.')

        try:
            thing = json.loads(raw_json, 'utf-8')
        except ValueError:
            raise falcon.HTTPError(falcon.HTTP_753,
                                   'Malformed JSON',
                                   'Could not decode the request body. The '
                                   'JSON was incorrect.')

        try:
            proper_thing = self.db.add_thing(thing)

        except StorageError:
            raise falcon.HTTPError(falcon.HTTP_725,
                                   'Database Error',
                                   "Sorry, couldn't write your thing to the "
                                   'database. It worked on my machine.')

        resp.status = falcon.HTTP_201
        resp.location = '/%s/things/%s' % (user_id, proper_thing.id)

wsgi_app = api = falcon.API(before=[auth, check_media_type])

db = StorageEngine()
things = ThingsResource(db)
api.add_route('/{user_id}/things', things)