from base64 import urlsafe_b64encode
from urlparse import parse_qs, urlsplit, urlunsplit
from urllib import unquote, urlencode

from django.conf import settings
from django.core.files.storage import Storage
from django.core.files.storage import FileSystemStorage

from secret_hash import SecretHash


class SecretHash(SecretHash):
    SECRET_KEY = settings.SECRET_KEY
    SECRET_LIFESPAN = getattr(settings, 'SECRET_URL_LIFESPAN', 86400) #24h


class SecureStorageMixin(Storage):
    """Append some paramaters to make urls more secure and expire.

    Made to support nginx and its http_secure_link_module:
    http://wiki.nginx.org/HttpSecureLinkModule

    The secure link module is not compiled with nginx by default. If
    you're using Ubuntu like me, apt-get install nginx-extras to get it.

    Here's how NGINX can be set up if your secret is "SECRET$KEY123":
    (NGINX can't natively escape dollar sign literals, so use ${dollar})

    geo $dollar {
        default "$";
    }
    server {
        ...
        location /media {
            secure_link $arg_key,$arg_exp;
            secure_link_md5 SECRET${dollar}KEY123$arg_exp$uri;
            # If the hash is incorrect then $secure_link is a null string.
            if ($secure_link = "") {
                return 403;
            }
            # The current local time is greater than the specified expiration.
            if ($secure_link = "0") {
                return 403;
            }
            ...
        }
    }

    """
    def url(self, name):
        # Take the URL generated by super and break it up
        u = super(SecureStorageMixin, self).url(name)
        scheme, netloc, path, query_string, fragment = urlsplit(u)
        query_params = parse_qs(query_string)

        # Generate the extra parameters and reconstruct the URL.
        hash = SecretHash(unquote(path))
        query_params['key'] = [hash.key]
        query_params['exp'] = [hash.expires]
        new_query_string = urlencode(query_params, doseq=True)
        return urlunsplit((scheme, netloc, path, new_query_string, fragment))


class SecureFileSystemStorage(SecureStorageMixin, FileSystemStorage): pass