--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gpp/forums/unread.py	Sun Oct 11 19:10:54 2009 +0000
@@ -0,0 +1,99 @@
+"""
+This file contains routines for implementing the "has unread" feature. 
+Forums, topics, and posts are displayed with a visual indication if they have
+been read or not.
+"""
+import datetime
+
+from forums.models import ForumLastVisit, TopicLastVisit, Topic
+
+
+THRESHOLD = datetime.timedelta(days=7)
+
+
+def get_forum_unread_status(qs, user):
+    if not user.is_authenticated():
+        for forum in qs:
+            forum.has_unread = False
+        return
+
+    now = datetime.datetime.now()
+    min_date = now - THRESHOLD
+
+    # retrieve ForumLastVisit records in one SQL query
+    forum_ids = [forum.id for forum in qs]
+    flvs = ForumLastVisit.objects.filter(user=user, 
+            forum__in=forum_ids).select_related()
+    flvs = dict([(flv.forum.id, flv) for flv in flvs])
+
+    for forum in qs:
+        # Edge case: forum has no posts
+        if forum.last_post is None:
+            forum.has_unread = False
+            continue
+
+        # Get the ForumLastVisit record
+        if forum.id in flvs:
+            flv = flvs[forum.id]
+        else:
+            # One doesn't exist, create a default one for next time,
+            # mark it as having no unread topics, and bail.
+            flv = ForumLastVisit(user=user, forum=forum)
+            flv.begin_date = now
+            flv.end_date = now
+            flv.save()
+            forum.has_unread = False
+            continue
+
+        # If the last visit record was too far in the past,
+        # catch that user up and mark as no unreads.
+        if now - flv.end_date > THRESHOLD:
+            forum.catchup(user, flv)
+            forum.has_unread = False
+            continue
+
+        # Check the easy cases first. Check the last_post in the
+        # forum. If created after the end_date in our window, there
+        # are new posts. Likewise, if before the begin_date in our window,
+        # there are no new posts.
+        if forum.last_post.creation_date > flv.end_date:
+            forum.has_unread = True
+        elif forum.last_post.creation_date < flv.begin_date:
+            if not flv.is_caught_up():
+                forum.catchup(user, flv)
+            forum.has_unread = False
+        else:
+            # Going to have to examine the topics in our window.
+            # First adjust our window if it is too old.
+            if now - flv.begin_date > THRESHOLD:
+                flv.begin_date = min_date
+                flv.save()
+                TopicLastVisit.objects.filter(user=user, topic__forum=forum,
+                        last_visit__lt=min_date).delete()
+
+            topics = Topic.objects.filter(creation_date__gt=flv.begin_date)
+            tracked_topics = TopicLastVisit.objects.filter(user=user,
+                    topic__forum=forum, last_visit__gt=flv.begin_date)
+
+            # If the number of topics created since our window was started 
+            # is greater than the tracked topic records, then there are new
+            # posts.
+            if topics.count() > tracked_topics.count():
+                forum.has_unread = True
+                continue
+
+            tracked_dict = dict([(t.id, t) for t in tracked_topics])
+
+            for topic in topics:
+                if topic.id in tracked_dict:
+                    if topic.update_date > tracked_dict[topic.id].last_visit:
+                        forum.has_unread = True
+                        continue
+                else:
+                    forum.has_unread = True
+                    continue
+
+            # If we made it through the above loop without continuing, then
+            # we are all caught up.
+            forum.catchup(user, flv)
+            forum.has_unread = False