Rating versioning and auditing

This blueprint describes a new functionnality for CK:
- add the ability to version a set of rating rules
- store version along rating computation
- add applicabilities

CK Rating versioning and auditing
#################################

Today, CK store only a rating value with no possibility to recover how this value was computed.
This blueprint proposes to add versioning and auditing capabilities to CK for the hashmap
module.

Ruleset
=======

Description
-----------

A ruleset is used to identify a set of rating rules in time.

Only one ruleset can be active and used for computation at a time.

A ruleset is active until another one replace it.

Ruleset model
-------------

A *ruleset* is defined as:

* id: a unique id
* descr [optional]: a description
* Rating rules: some rating rules
* Activation date: date when the ruleset should be effective and used for computation
* states: append-only state list. last back-inserted item is the current state

Ruleset state model
-------------------

A *state_item* is defined as:

* state: an enum based state indicator
* created-at: state creation date
* created-by: user id (can be the CK service user)

Ruleset state has the following life-cycle:

    draft <--> commited --> active --> archived.

In *draft* state, a ruleset can be modify.

In *commited* state, a ruleset is made available to the CK engine to be used. For modification,
ruleset state should be reverted to *draft*

In *active* state, the ruleset is activily used for rating computation. It cannot be modified and
can only evolve to *archived* state

In *archived* state, the ruleset is no more used and is archived for auditing purposes.

Ruleset actions
---------------

Create a ruleset
^^^^^^^^^^^^^^^^

A user can create a new ruleset (state: *draft*) from scratch, by copy or by import.

Commit a ruleset
^^^^^^^^^^^^^^^^

A user can commit a ruleset.

Revert a ruleset
^^^^^^^^^^^^^^^^

A user can revert a commited ruleset to draft.

Activate a ruleset
^^^^^^^^^^^^^^^^^^

A user can activate a particular ruleset.
This action automatically archived the current active ruleset.

Ruleset collection actions
--------------------------

List rulesets
^^^^^^^^^^^^^

A user can query for a list of ruleset.
A set of filters can be provided to restrict outputs

Get ruleset
^^^^^^^^^^^

A user can query for a ruleset details (values + state history)

Storage modification
====================

any rating record should embed the current active ruleset id

Orchestrator behavior modification
==================================

At each period, the orchestrator should evaluate the list of commited rulesets in order to
check if a new ruleset should be actived (according to the activation date).

The check is done regarding the collected data date.