Merge pull request #654 from YunoHost/trigger-actions-when-changing-settings

[enh] Be able to define hook to trigger when changing a setting

src/yunohost/settings.py

@@ -115,10 +115,18 @@ def settings_set(key, value):
         raise YunohostError('global_settings_unknown_type', setting=key,
                             unknown_type=key_type)
 
+    old_value = settings[key].get("value")
     settings[key]["value"] = value
-
     _save_settings(settings)
 
+    # TODO : whatdo if the old value is the same as
+    # the new value...
+    try:
+        trigger_post_change_hook(key, old_value, value)
+    except Exception as e:
+        logger.error("Post-change hook for setting %s failed : %s" % (key, e))
+        raise
+
 
 def settings_reset(key):
     """
@@ -235,3 +243,45 @@ def _save_settings(settings, location=SETTINGS_PATH):
             settings_fd.write(result)
     except Exception as e:
         raise YunohostError('global_settings_cant_write_settings', reason=e)
+
+
+# Meant to be a dict of setting_name -> function to call
+post_change_hooks = {}
+
+
+def post_change_hook(setting_name):
+    def decorator(func):
+        assert setting_name in DEFAULTS.keys(), "The setting %s does not exists" % setting_name
+        assert setting_name not in post_change_hooks, "You can only register one post change hook per setting (in particular for %s)" % setting_name
+        post_change_hooks[setting_name] = func
+        return func
+    return decorator
+
+
+def trigger_post_change_hook(setting_name, old_value, new_value):
+    if setting_name not in post_change_hooks:
+        logger.debug("Nothing to do after changing setting %s" % setting_name)
+        return
+
+    f = post_change_hooks[setting_name]
+    f(setting_name, old_value, new_value)
+
+
+# ===========================================
+#
+# Actions to trigger when changing a setting
+# You can define such an action with :
+#
+# @post_change_hook("your.setting.name")
+# def some_function_name(setting_name, old_value, new_value):
+#     # Do some stuff
+#
+# ===========================================
+
+
+#@post_change_hook("example.int")
+#def myfunc(setting_name, old_value, new_value):
+#    print("In hook")
+#    print(setting_name)
+#    print(old_value)
+#    print(new_value)