# see http://code.djangoproject.com/ticket/3777

from django import http

class FilterPersistMiddleware(object):
    def process_request(self, request):
        if request.method != 'GET':
            return None
        
        path = request.path
        if path.find('/admin/') != -1: # Dont waste time if we are not in admin
            query_string = request.META['QUERY_STRING']
            key = 'key' + path.replace('/','_')
            if not request.META.has_key('HTTP_REFERER'):
                return None
            if query_string: # Don't modify but save new queries
                request.session[key] = query_string
                return None
            
            session = request.session
            if session.get('redirected', False): # so that we dont loop once redirected
                del session['redirected']
                return None

            referrer = request.META['HTTP_REFERER'].split('?')[0]
            referrer = referrer[referrer.find('/admin'):len(referrer)]

            if path == referrer: # We are in same page as before
                if query_string == '': # Filter is empty, delete it
                    if session.get(key,False):
                        del session[key]
                    return None
                request.session[key] = query_string
            else: # We are are coming from another page, restore filter if available
                if session.get(key, False):
                    query_string=request.session.get(key)
                    redirect_to = path+'?'+query_string
                    request.session['redirected'] = True
                    return http.HttpResponseRedirect(redirect_to)
                else:
                    return None
        else:
            return None