Introducing endpoint for stats

This endpoint can be queried on a daily basis to retrieve cloud usage  stats. For assets and comments we take into considerations only those who belong to public projects.

cloud/stats/__init__.py

@@ -0,0 +1,47 @@
+"""Interesting usage metrics"""
+
+from flask import current_app
+
+pipeline = [
+    {'$match': {'_deleted': {'$ne': 'true'}}},
+    {
+        '$lookup':
+            {
+                'from': "projects",
+                'localField': "project",
+                'foreignField': "_id",
+                'as': "project",
+            }
+    },
+    {
+        '$unwind':
+            {
+                'path': '$project',
+            }
+    },
+    {
+        '$project':
+            {
+                'p.is_private': 1,
+            }
+    },
+    {'$match': {'p.is_private': {'$ne': True}}},
+    {'$count': 'tot'}
+]
+
+
+def count_nodes(query=None) -> int:
+    c = current_app.db()['nodes']
+    # If we provide a query, we extend the first $match step in the aggregation pipeline with
+    # with the extra parameters (for example node_type)
+    if query:
+        pipeline[0]['$match'].update(query)
+    # Return either a list with one item or an empty list
+    r = list(c.aggregate(pipeline=pipeline))
+    count = 0 if not r else r[0]['tot']
+    return count
+
+
+def count_users() -> int:
+    u = current_app.db()['users']
+    return u.count()