add a log rotation worker

Fixes #609.

data/model/log.py

@@ -124,3 +124,38 @@ def get_repository_usage():
           .where(LogEntry.datetime >= one_month_ago)
           .group_by(LogEntry.ip, LogEntry.repository)
           .count())
+
+
+def get_stale_logs_start_id():
+  """ Gets the oldest log entry. """
+  try:
+    return (LogEntry
+            .select(LogEntry.id)
+            .order_by(LogEntry.id)
+            .limit(1)
+            .tuples())[0][0]
+  except IndexError:
+    return None
+
+
+def get_stale_logs_end_id(cutoff_date):
+  """ Gets the most recent ID created before the cutoff_date. """
+  try:
+    return (LogEntry
+            .select(LogEntry.id)
+            .where(LogEntry.datetime <= cutoff_date)
+            .order_by(LogEntry.id.desc())
+            .limit(1)
+            .tuples())[0][0]
+  except IndexError:
+    return None
+
+
+def get_stale_logs(start_id, end_id):
+  """ Returns all the logs with IDs between start_id and end_id inclusively. """
+  return LogEntry.select().where((LogEntry.id >= start_id), (LogEntry.id <= end_id))
+
+
+def delete_stale_logs(start_id, end_id):
+  """ Deletes all the logs with IDs between start_id and end_id. """
+  LogEntry.delete().where((LogEntry.id >= start_id), (LogEntry.id <= end_id)).execute()