14. Change event producer config settings
#########################################

Status
******

**Accepted**

Context
*******

In a previous ADR, we set the structure for the event bus producing configuration to a dictionary like the following:

.. code-block:: python

    { 'org.openedx.content_authoring.xblock.published.v1': [
           {'topic': 'content-authoring-xblock-lifecycle', 'event_key_field': 'xblock_info.usage_key', 'enabled': True},
           {'topic': 'content-authoring-xblock-published', 'event_key_field': 'xblock_info.usage_key', 'enabled': False},
       ],
       'org.openedx.content_authoring.xblock.deleted.v1': [
           {'topic': 'content-authoring-xblock-lifecycle', 'event_key_field': 'xblock_info.usage_key', 'enabled': True},
       ],
   }

While attempting to implement this for edx-platform, we came across some problems with using this structure. In particular, it results in ambiguity
because maintainers can accidentally add something like
``{'topic': 'content-authoring-xblock-lifecycle', 'event_key_field': 'xblock_info.usage_key', 'enabled': True}`` and
``{'topic': 'content-authoring-xblock-lifecycle', 'event_key_field': 'xblock_info.usage_key', 'enabled': False}`` to the same event_type.
Moreover, enabling/disabling an existing event/topic pair requires reaching into the structure, searching for the dictionary with the correct topic, and modifying
the existing object, which is awkward.

This ADR aims to propose a new structure that will provide greater flexibility in using this configuration.

Decision
********

The new EVENT_BUS_PRODUCER_CONFIG will have the following configuration format:

.. code-block:: python

   # .. setting_name: EVENT_BUS_PRODUCER_CONFIG
   # .. setting_default: {}
   # .. setting_description: Dictionary of event_types to dictionaries for topic related configuration.
   #    Each topic configuration dictionary uses the topic as a key and contains a flag called `enabled`
   #    denoting whether the event will be and `event_key_field` which is a period-delimited string path
   #    to event data field to use as event key.
   #    Note: The topic names should not include environment prefix as it will be dynamically added based on
   #    EVENT_BUS_TOPIC_PREFIX setting.
   EVENT_BUS_PRODUCER_CONFIG = {
       'org.openedx.content_authoring.xblock.published.v1': {
           'content-authoring-xblock-lifecycle': {'event_key_field': 'xblock_info.usage_key', 'enabled': False},
           'content-authoring-xblock-published': {'event_key_field': 'xblock_info.usage_key', 'enabled': True}
       },
       'org.openedx.content_authoring.xblock.deleted.v1': {
           'content-authoring-xblock-lifecycle': {'event_key_field': 'xblock_info.usage_key', 'enabled': True},
       },
   }

A new ``merge_producer_configs`` method will be added to openedx-events.event_bus to make it easier to correctly determine the config map from multiple sources.

Consequences
************

* As long as the implementing IDA calls ``merge_producer_configs``, maintainers can add existing topics to new event_types without having to recreate the whole dictionary
* There is no ambiguity about whether an event/topic pair is enabled or disabled