Integrating XBlocks with edx-platform
=====================================

The edX LMS and Studio have several features that are extensions of the core XBlock
libraries (https://xblock.readthedocs.org). These features are listed below.

* `LMS`_
* `Studio`_
* `Testing`_
* `Deploying your XBlock`_

LMS
---

Runtime Features
~~~~~~~~~~~~~~~~

These are properties and methods available on ``self.runtime`` when a view or handler is executed by the LMS.

* anonymous_student_id: An identifier unique to the student in the particular course
  that the block is being executed in. The same student in two different courses
  will have two different ids.

* publish(event): Emit events to the surrounding system. Events are dictionaries with
  at least the key 'event_type', which identifies the other fields.

  TODO: Link to the authoritive list of event types.

In the future, these are likely to become more formal XBlock services (one related to users,
and the other to event publishing).

Class Features
~~~~~~~~~~~~~~

These are class attributes or functions that can be provided by an XBlock to customize behaviour
in the LMS.

* student_view (XBlock view): This is the view that will be rendered to display
  the XBlock in the LMS.
* has_score (class property): True if this block should appear in the LMS progress page.
* get_progress (method): See documentation in x_module.py:XModuleMixin.get_progress.
* icon_class (class property): This can be one of (``other``, ``video``, or ``problem``), and
  determines which icon appears in edx sequence headers. There is currently no way to provide
  a different icon.

Grading
~~~~~~~

To participate in the course grade, an XBlock should set ``has_score`` to ``True``, and
should ``publish`` a ``grade`` event whenever the grade changes. The ``grade`` event is a
dictionary of the following form::

    {
        'event_type': 'grade',
        'value': <number>,
        'max_value': <number>,
    }

The grade event represents a grade of ``value/max_value`` for the current user.

Restrictions
~~~~~~~~~~~~

* A block can't modify the value of any field with a scope where the ``user`` property
  is ``UserScope.NONE``.

Studio
------

Class Features
~~~~~~~~~~~~~~

* studio_view (XBlock.view): The view used to render an editor in Studio.

* non_editable_metadata_fields (property): A list of :class:`~xblock.fields.Field` objects that
  shouldn't be displayed in the default editing view for Studio.

Restrictions
~~~~~~~~~~~~

* A block can't modify the value of any field with a scope where the ``user`` property
  is not ``UserScope.NONE``.


Testing
-------

These instructions are temporary. Once XBlocks are fully supported by edx-platform
(both the LMS and Studio), installation and testing will be much more straightforward.

To enable an XBlock for testing in your devstack (https://github.com/edx/configuration/wiki/edX-Developer-Stack):

#.  Install your block::

        $ vagrant ssh
        vagrant@precise64:~$ sudo -u edxapp /edx/bin/pip.edxapp install /path/to/your/block

#.  Enable the block

    #.  In ``edx-platform/lms/envs/common.py``, uncomment::

        # from xmodule.x_module import prefer_xmodules
        # XBLOCK_SELECT_FUNCTION = prefer_xmodules

    #.  In ``edx-platform/cms/envs/common.py``, uncomment::

        # from xmodule.x_module import prefer_xmodules
        # XBLOCK_SELECT_FUNCTION = prefer_xmodules

    #.  In ``edx-platform/cms/envs/common.py``, change::

            'ALLOW_ALL_ADVANCED_COMPONENTS': False,

        to::

            'ALLOW_ALL_ADVANCED_COMPONENTS': True,

#.  Add the block to your courses' advanced settings in Studio

    #. Log in to Studio, and open your course
    #. Settings -> Advanced Settings
    #. Change the value for the key ``"advanced_modules"`` to ``["your-block"]``

#.  Add your block into your course

    #. Edit a unit
    #. Advanced -> your-block

Note the name ``your-block`` used in Studio must exactly match the key you used to add your
block to your ``setup.py`` ``entry_points`` list.


Deploying your XBlock
---------------------

To deploy your block to your own hosted version of edx-platform, you need to install it
into the virtualenv that the platform is running out of, and add to the list of ``ADVANCED_COMPONENT_TYPES``
in ``edx-platform/cms/djangoapps/contentstore/views/component.py``.
