From 37172efce084b7371820f04b6ae840fa5cbb8c52 Mon Sep 17 00:00:00 2001
From: Friedrich Lindenberg <friedrich@pudo.org>
Date: Wed, 13 Jul 2011 18:20:23 +0200
Subject: [PATCH] basic event logic layer: create an event in various
 eventstreams, retrieve and render (with a renderer class)

---
 datahub/logic/event.py     | 46 ++++++++++++++++++++++++++++++++++++--
 datahub/logic/renderers.py | 35 +++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+), 2 deletions(-)
 create mode 100644 datahub/logic/renderers.py

diff --git a/datahub/logic/event.py b/datahub/logic/event.py
index 79d73a9..a11fa09 100644
--- a/datahub/logic/event.py
+++ b/datahub/logic/event.py
@@ -1,5 +1,8 @@
-from datahub.exc import NotFound
-from datahub.model import Event
+from datahub.core import db
+from datahub.exc import NotFound, InternalError
+from datahub.model import Event, EventStreamEntry
+
+from datahub.logic.renderers import RENDERERS
 
 def get(id):
     """ Get will try to find an event and return None if no event
@@ -12,3 +15,42 @@ def find(id):
     if event is None:
         raise NotFound('No such event: %s' % id)
     return event
+
+def latest_by_stream(entity_type, entity_id, limit=50):
+    """ Fetch the `limit` latest events that occured on the given
+    event stream. """
+    events = Event.query.join(EventStreamEntry)
+    events = events.filter(EventStreamEntry.entity_type==entity_type)
+    events = events.filter(EventStreamEntry.entity_id==entity_id)
+    events = events.order_by(Event.time.desc())
+    events = events.limit(limit)
+    return events.all()
+
+def latest_by_entity(entity, limit=50):
+    """ Get events for a specific entity. """
+    return latest_by_stream(entity.__tablename__, entity.id, 
+                            limit=limit)
+
+def emit(event, streams=[]):
+    """ Unlike the other logic.*.create methods, this function 
+    expects an instantiated Event object to be passed in. As there
+    are many different event types, this seemed the right thing to
+    do. """
+    streams = set(streams)
+    if not event.account in streams:
+        streams.add(event.account)
+    db.session.add(event)
+    for stream in streams:
+        entry = EventStreamEntry(stream.__tablename__, stream.id, 
+                                 event)
+        db.session.add(entry)
+    db.session.flush()
+
+def renderer(event):
+    """ Retrieve and instantiate an appropriate renderer for this 
+    event. """
+    try:
+        return RENDERERS[type(event)](event)
+    except KeyError:
+        raise InternalError('No renderer for %s' % type(event))
+
diff --git a/datahub/logic/renderers.py b/datahub/logic/renderers.py
new file mode 100644
index 0000000..11da7d8
--- /dev/null
+++ b/datahub/logic/renderers.py
@@ -0,0 +1,35 @@
+#import cgi
+from flask import url_for
+
+from datahub.model.event import ResourceCreatedEvent
+
+class EventRenderer(object): 
+    html_template = ''
+    plain_template = ''
+
+    def __init__(self, event):
+        self.event = event
+
+    def params(self):
+        return self.event.data
+
+    def __html__(self):
+        return self.html_template % self.params()
+
+    def __unicode__(self):
+        return self.plain_template % self.params()
+
+class ResourceCreatedEventRenderer(EventRenderer):
+    html_template = '''has <verb>created</verb> 
+        <a href='%(url)s'>%(owner)s/%(resource)s</a>'''
+
+    def params(self):
+        data = self.event.data.copy()
+        data['url'] = url_for('node', owner=data['owner'], 
+                              node=data['resource'])
+        return data
+
+RENDERERS = {
+    ResourceCreatedEvent: ResourceCreatedEventRenderer
+    }
+