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import math
import random
import logging
from django.contrib.sites.models import Site
from django.core.urlresolvers import reverse
import brevisurl.settings
from brevisurl import Error
from brevisurl.backends.base import BaseBrevisUrlBackend
from brevisurl.models import ShortUrl
from brevisurl.utils import absurl
log = logging.getLogger(__name__)
class TokensExhaustedError(Error):
"""Exception is raised when tokens are exhausted."""
class BrevisUrlBackend(BaseBrevisUrlBackend):
def shorten_url(self, original_url):
"""
:raises: ImproperlyConfigured, django.core.exceptions.ValidationError
:raises: brevisurl.backends.local.TokensExhaustedError
"""
try:
short_url = ShortUrl.objects.get(backend=self.class_path, original_url=original_url)
log.info('Url "%s" already shortened to "%s"', original_url, short_url.shortened_url)
return short_url
except ShortUrl.DoesNotExist:
pass
try:
short_url = ShortUrl()
if self.kwargs.get('domain') is not None:
# Domain is present in keyword arguments supplied by constructor.
domain = self.kwargs.get('domain')
elif brevisurl.settings.LOCAL_BACKEND_DOMAIN is not None:
# Domain is defined in settings.
domain = brevisurl.settings.LOCAL_BACKEND_DOMAIN
else:
# Domain is taken from django site framework.
domain = Site.objects.get_current().domain
# Saving newly generated shortened url.
short_url.original_url = original_url
short_url.shortened_url = absurl(domain=domain, path=reverse('brevisurl_redirect',
kwargs={'token': self.__generate_token()}))
short_url.backend = self.class_path
short_url.save()
log.info('Url "%s" shortened to "%s"', original_url, short_url.shortened_url)
return short_url
except Exception:
if self.fail_silently:
return None
else:
log.exception('Unknown exception raised while shortening url "%s"', original_url)
raise
def __generate_token(self):
chars = brevisurl.settings.LOCAL_BACKEND_TOKEN_CHARS
size = brevisurl.settings.LOCAL_BACKEND_TOKEN_LENGTH
if ShortUrl.objects.count() >= math.pow(len(chars), size):
raise TokensExhaustedError('Consider incrementing the token length or change the char list')
random.shuffle(chars)
while True:
token = ''.join([random.choice(chars) for x in range(size)])
if not ShortUrl.objects.filter(backend=self.class_path, shortened_url__endswith=token).count():
break
return token
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