--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gpp/forums/latest.py	Wed Dec 07 01:08:54 2011 +0000
@@ -0,0 +1,107 @@
+"""
+This module maintains the latest posts datastore. The latest posts are often
+needed by RSS feeds, "latest posts" template tags, etc. This module listens for
+the post_content_update signal, then bundles the post up and stores it by forum
+ID in Redis. We also maintain a combined forums list. This allows quick
+retrieval of the latest posts and avoids some slow SQL queries.
+
+"""
+import datetime
+import time
+
+from django.dispatch import receiver
+from django.utils import simplejson
+
+from forums.signals import post_content_update
+from forums.models import Forum
+from core.services import get_redis_connection
+
+
+# This constant controls how many latest posts per forum we store
+MAX_POSTS = 50
+
+
+@receiver(post_content_update, dispatch_uid='forums.latest_posts')
+def on_post_update(sender, **kwargs):
+    """
+    This function is our signal handler, called when a post has been updated.
+    We only care about newly created posts, and ignore updates.
+
+    We serialize a post to JSON then store in two lists in Redis:
+        1. The list for the post's parent forum
+        2. The combined forum list
+
+    Note that we only store posts from public forums.
+
+    """
+    # ignore non-new posts
+    if not kwargs['created']:
+        return
+
+    # ignore posts from non-public forums
+    public_forums = Forum.objects.public_forum_ids()
+    if sender.topic.forum.id not in public_forums:
+        return
+
+    # serialize post attributes
+    post_content = {
+        'id': sender.id,
+        'title': sender.topic.name,
+        'content': sender.html,
+        'author': sender.user.username,
+        'pubdate': int(time.mktime(sender.creation_date.timetuple())),
+        'forum_name': sender.topic.forum.name,
+        'url': sender.get_absolute_url()
+    }
+
+    s = simplejson.dumps(post_content)
+
+    # store in Redis
+
+    redis = get_redis_connection()
+    pipeline = redis.pipeline()
+
+    key = 'forums:latest:%d' % sender.topic.forum.id
+
+    pipeline.lpush(key, s)
+    pipeline.ltrim(key, 0, MAX_POSTS - 1)
+
+    # store in the combined feed; yes this wastes some memory storing it twice,
+    # but it makes things much easier
+
+    key = 'forums:latest:*'
+
+    pipeline.lpush(key, s)
+    pipeline.ltrim(key, 0, MAX_POSTS - 1)
+
+    pipeline.execute()
+
+
+def get_latest_posts(num_posts=MAX_POSTS, forum_id=None):
+    """
+    This function retrieves num_posts latest posts for the forum with the given
+    forum_id. If forum_id is None, the posts are retrieved from the combined
+    forums datastore. A list of dictionaries is returned. Each dictionary
+    contains information about a post.
+
+    """
+    key = 'forums:latest:%d' % forum_id if forum_id else 'forums:latest:*'
+
+    num_posts = max(0, min(MAX_POSTS, num_posts))
+
+    if num_posts == 0:
+        return []
+
+    redis = get_redis_connection()
+    raw_posts = redis.lrange(key, 0, num_posts - 1)
+
+    posts = []
+    for raw_post in raw_posts:
+        post = simplejson.loads(raw_post)
+
+        # fix up the pubdate; turn it back into a datetime object
+        post['pubdate'] = datetime.datetime.fromtimestamp(post['pubdate'])
+
+        posts.append(post)
+
+    return posts