import md5

import re

from django.conf import settings

from django import http

from django.core.mail import mail_managers

from django.utils.http import urlquote

from django.core import urlresolvers

class CommonMiddleware(object):

    """

    "Common" middleware for taking care of some basic operations:

        - Forbids access to User-Agents in settings.DISALLOWED_USER_AGENTS

        - URL rewriting: Based on the APPEND_SLASH and PREPEND_WWW settings,

          this middleware appends missing slashes and/or prepends missing

          "www."s.

            - If APPEND_SLASH is set and the initial URL doesn't end with a

              slash, and it is not found in urlpatterns, a new URL is formed by

              appending a slash at the end. If this new URL is found in

              urlpatterns, then an HTTP-redirect is returned to this new URL;

              otherwise the initial URL is processed as usual. 

        - ETags: If the USE_ETAGS setting is set, ETags will be calculated from

          the entire page content and Not Modified responses will be returned

          appropriately.

    """

    def process_request(self, request):

        """

        Check for denied User-Agents and rewrite the URL based on

        settings.APPEND_SLASH and settings.PREPEND_WWW

        """

        # Check for denied User-Agents

        if 'HTTP_USER_AGENT' in request.META:

            for user_agent_regex in settings.DISALLOWED_USER_AGENTS:

                if user_agent_regex.search(request.META['HTTP_USER_AGENT']):

                    return http.HttpResponseForbidden('<h1>Forbidden</h1>')

        # Check for a redirect based on settings.APPEND_SLASH

        # and settings.PREPEND_WWW

        host = request.get_host()

        old_url = [host, request.path]

        new_url = old_url[:]

        if (settings.PREPEND_WWW and old_url[0] and

                not old_url[0].startswith('www.')):

            new_url[0] = 'www.' + old_url[0]

        # Append a slash if APPEND_SLASH is set and the URL doesn't have a

        # trailing slash and there is no pattern for the current path

        if settings.APPEND_SLASH and (not old_url[1].endswith('/')):

            try:

                urlresolvers.resolve(request.path)

            except urlresolvers.Resolver404:

                new_url[1] = new_url[1] + '/'

                if settings.DEBUG and request.method == 'POST':

                    raise RuntimeError, (""

                    "You called this URL via POST, but the URL doesn't end "

                    "in a slash and you have APPEND_SLASH set. Django can't "

                    "redirect to the slash URL while maintaining POST data. "

                    "Change your form to point to %s%s (note the trailing "

                    "slash), or set APPEND_SLASH=False in your Django "

                    "settings.") % (new_url[0], new_url[1])

        if new_url != old_url:

            # Redirect if the target url exists

            try:

                urlresolvers.resolve(new_url[1])

            except urlresolvers.Resolver404:

                pass

            else:

                if new_url[0]:

                    newurl = "%s://%s%s" % (

                        request.is_secure() and 'https' or 'http',

                        new_url[0], urlquote(new_url[1]))

                else:

                    newurl = urlquote(new_url[1])

                if request.GET:

                    newurl += '?' + request.GET.urlencode()

                return http.HttpResponsePermanentRedirect(newurl)

        return None

    def process_response(self, request, response):

        "Check for a flat page (for 404s) and calculate the Etag, if needed."

        if response.status_code == 404:

            if settings.SEND_BROKEN_LINK_EMAILS:

                # If the referrer was from an internal link or a non-search-engine site,

                # send a note to the managers.

                domain = request.get_host()

                referer = request.META.get('HTTP_REFERER', None)

                is_internal = _is_internal_request(domain, referer)

                path = request.get_full_path()

                if referer and not _is_ignorable_404(path) and (is_internal or '?' not in referer):

                    ua = request.META.get('HTTP_USER_AGENT', '<none>')

                    ip = request.META.get('REMOTE_ADDR', '<none>')

                    mail_managers("Broken %slink on %s" % ((is_internal and 'INTERNAL ' or ''), domain),

                        "Referrer: %s\nRequested URL: %s\nUser agent: %s\nIP address: %s\n" \

                                  % (referer, request.get_full_path(), ua, ip))

                return response

        # Use ETags, if requested.

        if settings.USE_ETAGS:

            if response.has_header('ETag'):

                etag = response['ETag']

            else:

                etag = md5.new(response.content).hexdigest()

            if response.status_code >= 200 and response.status_code < 300 and request.META.get('HTTP_IF_NONE_MATCH') == etag:

                cookies = response.cookies

                response = http.HttpResponseNotModified()

                response.cookies = cookies

            else:

                response['ETag'] = etag

        return response

def _is_ignorable_404(uri):

    "Returns True if a 404 at the given URL *shouldn't* notify the site managers"

    for start in settings.IGNORABLE_404_STARTS:

        if uri.startswith(start):

            return True

    for end in settings.IGNORABLE_404_ENDS:

        if uri.endswith(end):

            return True

    return False

def _is_internal_request(domain, referer):

    "Return true if the referring URL is the same domain as the current request"

    # Different subdomains are treated as different domains.

    return referer is not None and re.match("^https?://%s/" % re.escape(domain), referer)