rougail/docs/concepts.rst

Abstract presentation
=========================

Rougail, a powerful, free/open-source configuration manager and language that combines declaration, data validation, and templating in a single, declarative syntax.

It will be useful to:

- define variables (the structure) easily and their constraintes
- loads those variables
- generate variables documentation
- loads variables' values
- validate the variables and the overall consistency handling system
- generate custom table views
- export to different common format (YAML, Ansible, ...)
- ...

Why another configuration manager?
-------------------------------------

Using Rougail tansform end user consumer defined consistency rules into highly consistent business objects.
It's a configuration language designed to simplify and unify the way you define, validate, and generate configuration data.

In other word, making it easier to manage complex configurations across multiple environments.

Rougail is:

- a commandline
- a `Python <https://www.python.org/>`_ library
- a description language

What kind of configuration manager?
---------------------------------------------

At the time of the design of Rougail, there were structuring choices that defined the functioning of the tool.

The steps in Rougail can be explain as follows:

- loads the variable structured data
- loads the user data
- reads, validates, exports, document, ... the data

Structured data
~~~~~~~~~~~~~~~~~

Structured data is also called Rougail format.

.. glossary::

   structured data

       A configuration-first DSL (domain-specific language) designed for describing variables, consistency
       and describe the relationships between variables in a declarative style.

       The language is a mix of YAML ans Jinja Templating.

       It goes beyond traditional schema languages (like JSON Schema, OpenAPI, Cuelang)
       by combinig type systems, powerful validation, consistency of the configuration and documentation.

Structured data are commonly place in structure file.

User data
~~~~~~~~~~

.. glossary::

    user data

        User datas, as opposed to structured data, are datas that only concern the assignment of values
        and not the consistency of the variables between them.

        The variable's values are also called **user values**.

        The consistency field is outside of the user data scope.
        The consistency is handled in the :term:`structured datas <structured data>`\ 's scope.

Here a some user data examples:

- configuration files
- environment variables
- external sources
- command-line options
- a form

Output
~~~~~~~

Structured and user data form a coherent configuration useful for different purpose.

Output is here to define what kind of data we want.

And some output examples:

- term:`Tiramisu` object
- extract JSON
- extract to Ansible inventory
- documentation
- custom table views

.. list-table::
   :widths: 15 45
   :header-rows: 1

   * - Step

   * - Structured data

   * - User data

   * - Output

What kind of actor?
---------------------

It's clear that Rougail can be used in many contexts.

Here we'll define actor names. Obviously, these aren't the only possible actors.

We're just defining the actors within the Rougail context. Choice your own actor name if you wish to personnalize in your specific context.

.. glossary::

    integrator

        An integrator in the Rougail field is the person who writes the :term:`structure files <structure file>`\ .
        He has the responsibility of the integration process, that is,
        he defines the variables and the relationship between them, the variables that are allowed
        (or not) to be set, and so on. His responsabilites are the **structuration** and the **consistency**
        of the organisation of the variables between them.

.. glossary::

    operator

        An operator in the Rougail field is the person who assigns :term:`value`\ s to the pre-defined variables,
        his responsabilities are to set variable values correctly.

        The user :term:`value`\ s, that is the values that have been set by the operator, are of course type validated.
        The type validation is driven by the definitions in the :term:`structure file <structure file>`.

.. list-table::
   :widths: 15 45
   :header-rows: 1

   * - Step
     - Actor
     - Description

   * - Structured data
     - Integrator
     - The actor who defines the structure

   * - User data
     - Operator
     - The actor who sets the values

   * - Output
     - Operator or integrator
     - The actor who uses the variables with their values

Variable lifetime
----------------------

Rougail's is a configuration language and data validation tool designed to simplify defining, validating, and generating structured configuration and data.

Rougail aims to define variables.

Here we are talking about the variable lifetime.

The variable’s lifetime is the period between its creation and its destruction.

The lifecycle of a variable includes the generic stages (like, in the Python language):

.. list-table::
   :widths: 15 45
   :header-rows: 1

   * - Creation
     - Assignment
     - Reading
     - Destruction

   * - Variables are assigned a name and a type
     - The variable's value is modified
     - The variable's value is used
     - The variable terminates upon the destruction of the object

But other concepts are included in the lifecycle:

.. list-table::
   :widths: 15 45
   :header-rows: 1

   * - Permission
     - Documentation
     - Specialization

   * - Properties describe access constraints
     - Informations for variable documentation like description or help. Those informations are used to build documentation, changelog, ...
     - Define usage, selection,...


.. list-table::
   :widths: 15 45
   :header-rows: 1

   * - Step
     - Actor
     - Lifetime

   * - Structured data
     - Integrator
     - Creation

   * - User data
     - Operator
     - Assignment and permission

   * - Output
     - Operator or integrator
     - Reading, permission, documentation and specialization

Variable mutability
---------------------

Structured data
~~~~~~~~~~~~~~~~

When the integrator define the structure, variable are mutable.

Even if the default behavior is to conflict when multiple declarations for the same variable.

It's possible to explicitly allow to unifying (combined) multiple variables declarations.

User data
~~~~~~~~~~

It's no more possible to modifying variable definition.

Output
~~~~~~~

Variable definition settings are immutable.

.. list-table::
   :widths: 15 45
   :header-rows: 1

   * - Step
     - Actor
     - Lifetime
     - Variable mutability

   * - Structured data
     - Integrator
     - Creation + initialization
     - Mutable

   * - User data
     - Operator
     - Assignment and permission
     - Immutable

   * - Output
     - Operator or integrator
     - Reading, permission, documentation and specialization
     - Immutable

Value access
-------------

In the `structured data` step, there is no value, strictly speaking. It's a default value.
As other parameters, the default value is explicitly mutable.

In the `user data` step, we can modify the values. That's precisely the purpose of this step.
The configuration is said to be in `read write` mode.

But at the `output` step, it is obviously no longer possible to modify the value.
The configuration is said to be in `read only` mode.

.. attention::
   It is important not to confuse `value` and `calculated value`.
   The result of a calculation can change over time.
   In this case, the value does indeed correspond to the result of the calculation.

.. list-table::
   :widths: 15 45
   :header-rows: 1

   * - Step
     - Actor
     - Lifetime
     - Variable mutability
     - Value

   * - Structured data
     - Integrator
     - Creation + initialization
     - Mutable
     - Mutable default value

   * - User data
     - Operator
     - Assignment and permission
     - Immutable
     - Read write

   * - Output
     - Operator or integrator
     - Reading, permission, documentation and specialization
     - Immutable
     - Read only

Access control
-----------------

.. FIXME: duplicate from tutorial/properties.rst

Access control is achieved through `properties`.


.. glossary::

   property

       A property is a state (`disabled`, `mandatory`, `frozen`, `hidden`...)
       of a family or a variable.
       These properties change the usual behavior of a variable or family.

The properties can be defined permanently or according to the result of a calculation.

There is two main properties.

Hidden variable
~~~~~~~~~~~~~~~

A `hidden` variable is a variable whose value cannot be modified by the operator.

This could be an internal variable used by the integrator that is not supposed to change.

Or a variable that only makes sense in a particular context. Therefore, this variable can be hidden and then unhidden depending on the context.

Disabled variable
~~~~~~~~~~~~~~~~~

A `disabled` variable is a variable that will not be accessible to any of the actors (integrator and operator).

This property is generally used dynamically to remove access to the variable depending on the context.

.. list-table::
   :widths: 15 45
   :header-rows: 1

   * - Step
     - Actor
     - Lifetime
     - Variable mutability
     - Value
     - Access control

   * - Structured data
     - Integrator
     - Creation + initialization
     - Mutable
     - Mutable default value
     - N/A

   * - User data
     - Operator
     - Assignment and permission
     - Immutable
     - Read write
     - hidden + disabled

   * - Output
     - Operator or integrator
     - Reading, permission, documentation and specialization
     - Immutable
     - Read only
     - disabled + mandatory