loan: notifications #52

Implements #52 and resolves user story #24.

On after method of a transition we fire a signal with the class that was triggered and the loan that was affected.

invenio_circulation/signals.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2018 CERN.
+# Copyright (C) 2018 RERO.
+#
+# Invenio-Circulation is free software; you can redistribute it and/or modify
+# it under the terms of the MIT License; see LICENSE file for more details.
+
+"""Signals for Invenio-Circulation."""
+
+from blinker import Namespace
+
+_signals = Namespace()
+
+loan_state_changed = _signals.signal('loan-state-changed')
+"""Loan state changed signal.
+
+Its is broadcasted when a loan transitions to a different state.
+"""

invenio_circulation/transitions/base.py

@@ -15,6 +15,7 @@
 from ..api import is_item_available
 from ..errors import InvalidState, ItemNotAvailable, \
     TransitionConditionsFailed, TransitionConstraintsViolation
+from ..signals import loan_state_changed
 from ..utils import parse_date
 
 
@@ -124,4 +125,5 @@ def after(self, loan):
         """Commit record and index."""
         loan['transaction_date'] = loan['transaction_date'].isoformat()
         loan.commit()
-        # TODO: save to db and index loan here???
+        # TODO: save to db and index loan here, then broadcast the changes.
+        loan_state_changed.send(self, loan=loan)