bgneal@509: """
bgneal@509: This module maintains the latest posts datastore. The latest posts are often
bgneal@509: needed by RSS feeds, "latest posts" template tags, etc. This module listens for
bgneal@509: the post_content_update signal, then bundles the post up and stores it by forum
bgneal@509: ID in Redis. We also maintain a combined forums list. This allows quick
bgneal@509: retrieval of the latest posts and avoids some slow SQL queries.
bgneal@509: 
bgneal@509: """
bgneal@509: import datetime
bgneal@509: import time
bgneal@509: 
bgneal@509: from django.dispatch import receiver
bgneal@509: from django.utils import simplejson
bgneal@509: 
bgneal@509: from forums.signals import post_content_update
bgneal@509: from forums.models import Forum
bgneal@509: from core.services import get_redis_connection
bgneal@509: 
bgneal@509: 
bgneal@509: # This constant controls how many latest posts per forum we store
bgneal@509: MAX_POSTS = 50
bgneal@509: 
bgneal@509: 
bgneal@509: @receiver(post_content_update, dispatch_uid='forums.latest_posts')
bgneal@509: def on_post_update(sender, **kwargs):
bgneal@509:     """
bgneal@509:     This function is our signal handler, called when a post has been updated.
bgneal@509:     We only care about newly created posts, and ignore updates.
bgneal@509: 
bgneal@509:     We serialize a post to JSON then store in two lists in Redis:
bgneal@509:         1. The list for the post's parent forum
bgneal@509:         2. The combined forum list
bgneal@509: 
bgneal@509:     Note that we only store posts from public forums.
bgneal@509: 
bgneal@509:     """
bgneal@509:     # ignore non-new posts
bgneal@509:     if not kwargs['created']:
bgneal@509:         return
bgneal@509: 
bgneal@509:     # ignore posts from non-public forums
bgneal@509:     public_forums = Forum.objects.public_forum_ids()
bgneal@509:     if sender.topic.forum.id not in public_forums:
bgneal@509:         return
bgneal@509: 
bgneal@509:     # serialize post attributes
bgneal@509:     post_content = {
bgneal@509:         'id': sender.id,
bgneal@509:         'title': sender.topic.name,
bgneal@509:         'content': sender.html,
bgneal@509:         'author': sender.user.username,
bgneal@509:         'pubdate': int(time.mktime(sender.creation_date.timetuple())),
bgneal@509:         'forum_name': sender.topic.forum.name,
bgneal@509:         'url': sender.get_absolute_url()
bgneal@509:     }
bgneal@509: 
bgneal@509:     s = simplejson.dumps(post_content)
bgneal@509: 
bgneal@509:     # store in Redis
bgneal@509: 
bgneal@509:     redis = get_redis_connection()
bgneal@509:     pipeline = redis.pipeline()
bgneal@509: 
bgneal@509:     key = 'forums:latest:%d' % sender.topic.forum.id
bgneal@509: 
bgneal@509:     pipeline.lpush(key, s)
bgneal@509:     pipeline.ltrim(key, 0, MAX_POSTS - 1)
bgneal@509: 
bgneal@509:     # store in the combined feed; yes this wastes some memory storing it twice,
bgneal@509:     # but it makes things much easier
bgneal@509: 
bgneal@509:     key = 'forums:latest:*'
bgneal@509: 
bgneal@509:     pipeline.lpush(key, s)
bgneal@509:     pipeline.ltrim(key, 0, MAX_POSTS - 1)
bgneal@509: 
bgneal@509:     pipeline.execute()
bgneal@509: 
bgneal@509: 
bgneal@509: def get_latest_posts(num_posts=MAX_POSTS, forum_id=None):
bgneal@509:     """
bgneal@509:     This function retrieves num_posts latest posts for the forum with the given
bgneal@509:     forum_id. If forum_id is None, the posts are retrieved from the combined
bgneal@509:     forums datastore. A list of dictionaries is returned. Each dictionary
bgneal@509:     contains information about a post.
bgneal@509: 
bgneal@509:     """
bgneal@509:     key = 'forums:latest:%d' % forum_id if forum_id else 'forums:latest:*'
bgneal@509: 
bgneal@509:     num_posts = max(0, min(MAX_POSTS, num_posts))
bgneal@509: 
bgneal@509:     if num_posts == 0:
bgneal@509:         return []
bgneal@509: 
bgneal@509:     redis = get_redis_connection()
bgneal@509:     raw_posts = redis.lrange(key, 0, num_posts - 1)
bgneal@509: 
bgneal@509:     posts = []
bgneal@509:     for raw_post in raw_posts:
bgneal@509:         post = simplejson.loads(raw_post)
bgneal@509: 
bgneal@509:         # fix up the pubdate; turn it back into a datetime object
bgneal@509:         post['pubdate'] = datetime.datetime.fromtimestamp(post['pubdate'])
bgneal@509: 
bgneal@509:         posts.append(post)
bgneal@509: 
bgneal@509:     return posts