--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gpp/forums/middleware.py	Tue Dec 22 02:08:05 2009 +0000
@@ -0,0 +1,51 @@
+"""
+Middleware for the forums application.
+"""
+import datetime
+
+from django.core.cache import cache
+from django.conf import settings
+
+
+USER_ONLINE_TIMEOUT = datetime.timedelta(minutes=15)
+USERS_ONLINE_KEY = 'users_online'
+GUESTS_ONLINE_KEY = 'guests_online'
+USERS_CACHE_TIMEOUT = 60 * 60 * 24      # units are seconds
+
+
+class WhosOnline(object):
+    """
+    This middleware class keeps track of which registered users have
+    been seen recently, and the number of unique unregistered users.
+    We use the Django cache system to store this information.
+    This middleware should come after the authentication middleware,
+    as we count on the user attribute being attached to the request.
+    """
+
+    def process_request(self, request):
+        """
+        Keep track of who is online.
+        """
+        now = datetime.datetime.now()
+        cutoff = now - USER_ONLINE_TIMEOUT
+        users_online = cache.get(USERS_ONLINE_KEY, {})
+        guests_online = cache.get(GUESTS_ONLINE_KEY, {})
+
+        # update timestamp for user
+        if request.user.is_authenticated():
+            users_online[request.user.username] = now
+        else:
+            sid = request.COOKIES.get(settings.SESSION_COOKIE_NAME, '')
+            guests_online[sid] = now
+
+        # expire old records
+        for username, timestamp in users_online.items():
+            if timestamp < cutoff:
+                del users_online[username]
+
+        for sid, timestamp in guests_online.items():
+            if timestamp < cutoff:
+                del guests_online[sid]
+
+        cache.set(USERS_ONLINE_KEY, users_online, USERS_CACHE_TIMEOUT)
+        cache.set(GUESTS_ONLINE_KEY, guests_online, USERS_CACHE_TIMEOUT)