Add a `merge` command to do a simple left-right merge

I'm running this off a RPi at the moment, this is needed to get around the 2GB limit on a 32-bit MongoDB

metrik/merge.py

@@ -0,0 +1,47 @@
+from pymongo import MongoClient
+import logging
+import argparse
+
+
+def open_connection(host, port):
+    return MongoClient(host=host, port=port)
+
+
+def merge(con1, con2, database_name='metrik'):
+    database1 = con1[database_name]
+    database2 = con2[database_name]
+    collections = database1.collection_names()
+    for collection_name in collections:
+        collection1 = database1[collection_name]
+        collection2 = database2[collection_name]
+        for item in collection1.find():
+            if collection2.find({'_id': item['_id']}) is None:
+                collection2.save(item)
+                collection1.delete_one({'_id': item['_id']})
+            else:
+                logging.warning('Not moving item {} as the same ID already'
+                                ' exists in the `right` database.'.format(
+                    item['_id']
+                ))
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('-h', '--host-1', dest='host1',
+                        help='The `left` database to copy from')
+    parser.add_argument('-g', '--host-2', dest='host2',
+                        help='The `right` database to copy into')
+    parser.add_argument('-p', '--port-1', default=27017, dest='port1', type=int,
+                        help='The port number of the `left` database')
+    parser.add_argument('-o', '--port-2', default=27017, dest='port2', type=int,
+                        help='The port number of the `right` database')
+    parser.add_argument('-d', '--database', default='metrik',
+                        help='The database to merge from one host to the other')
+    args = parser.parse_args()
+    con1 = open_connection(args.host1, args.port1)
+    con2 = open_connection(args.host2, args.port2)
+    merge(con1, con2, args.database)
+
+
+if __name__ == '__main__':
+    main()

setup.py

@@ -33,7 +33,8 @@ setup(
     ],
     entry_points={
         'console_scripts': [
-            'metrik = metrik.batch:handle_commandline'
+            'metrik = metrik.batch:handle_commandline',
+            'metrik-merge = metrik.merge:main'
         ]
     }
 )