.. _sec-plugins-gettingstarted:

Getting Started
===============

Over the course of this little tutorial we'll build a full fledged, installable OctoPrint plugin that displays "Hello World!"
at various places throughout OctoPrint.

We'll start at the most basic form a plugin can take - just a couple of simple lines of Python code:

.. code-block:: python

   # coding=utf-8
   from __future__ import absolute_import

   __plugin_name__ = "Hello World"
   __plugin_version__ = "1.0"
   __plugin_description__ = "A quick \"Hello World\" example plugin for OctoPrint"

Saving this as ``helloworld.py`` in ``~/.octoprint/plugins`` yields you something resembling these log entries upon server startup::

   2015-01-27 11:14:35,124 - octoprint.server - INFO - Starting OctoPrint 1.2.0-dev-448-gd96e56e (devel branch)
   2015-01-27 11:14:35,124 - octoprint.plugin.core - INFO - Loading plugins from /home/pi/.octoprint/plugins, /home/pi/OctoPrint/src/octoprint/plugins and installed plugin packages...
   2015-01-27 11:14:36,135 - octoprint.plugin.core - INFO - Found 3 plugin(s): Hello World (1.0), CuraEngine (0.1), Discovery (0.1)

OctoPrint found that plugin in the folder and took a look into it. The name and the version it displays in that log
entry it got from the ``__plugin_name__`` and ``__plugin_version__`` lines. It also read the description from
``__plugin_description__`` and stored it in an internal data structure, but we'll just ignore this for now.

.. _sec-plugins-gettingstarted-sayinghello:

Saying hello: How to make the plugin actually do something
----------------------------------------------------------

Apart from being discovered by OctoPrint, our plugin does nothing yet. We want to change that. Let's make it print
"Hello World!" to the log upon server startup. Modify our ``helloworld.py`` like this:

.. code-block:: python
   :emphasize-lines: 4-8,13

   # coding=utf-8
   from __future__ import absolute_import

   import octoprint.plugin

   class HelloWorldPlugin(octoprint.plugin.StartupPlugin):
       def on_after_startup(self):
           self._logger.info("Hello World!")

   __plugin_name__ = "Hello World"
   __plugin_version__ = "1.0"
   __plugin_description__ = "A quick \"Hello World\" example plugin for OctoPrint"
   __plugin_implementations__ = [HelloWorldPlugin()]

and restart OctoPrint. You now get this output in the log::

   2015-01-27 11:17:10,792 - octoprint.plugins.helloworld - INFO - Hello World!

Neat, isn't it? We added a custom class that subclasses one of OctoPrint's :ref:`plugin mixins <sec-plugins-mixins>`
with :class:`~octoprint.plugin.StartupPlugin` and another control property, ``__plugin_implementations__``, that instantiates
our plugin class and tells OctoPrint about it. Taking a look at the documentation of :class:`~octoprint.plugin.StartupPlugin` we see that
this mixin offers two methods that get called by OctoPrint during startup of the server, :func:`~octoprint.plugin.StartupPlugin.on_startup` and
:func:`~octoprint.plugin.StartupPlugin.on_after_startup`. We decided to add our logging output by overriding :func:`~octoprint.plugin.StartupPlugin.on_after_startup`, but we could also have
used :func:`~octoprint.plugin.StartupPlugin.on_startup` instead, in which case our logging statement would be executed before the server was done starting
up and ready to serve requests.

You'll also note that we are using ``self._logger`` for logging. Where did that one come from? OctoPrint's plugin system
injects :ref:`a couple of useful objects <sec-plugins-infrastructure-injections>` into our plugin implementation classes,
one of those being a fully instantiated `python logger <https://docs.python.org/2/library/logging.html>`_ ready to be
used by your plugin. As you can see in the log output above, that logger uses the namespace ``octoprint.plugins.helloworld``
for our little plugin here, or more generally ``octoprint.plugins.<plugin identifier>``.

.. _sec-plugins-gettingstarted-growingup:

Growing up: How to make it distributable
----------------------------------------

If you now want to distribute this plugin to other OctoPrint users (since it is so awesome to be greeted upon server
startup), let's take a look at how you'd go about that now before our plugin gets more complicated.

You basically have two options to distribute your plugin. One would be about the exact same way we are using it now,
as a simple python file following the naming convention ``<plugin identifier>.py`` that your users add to their
``~/.octoprint/plugins`` folder. You already know how that works. But let's say you have more than just a simple plugin
that can be done in one file. Distributing multiple files and getting your users to install them in the right way
so that OctoPrint will be able to actually find and load them is certainly not impossible (see :ref:`the plugin distribution
documentation <sec-plugins-distribution>` if you want to take a closer look at that option), but we want to do it in the
best way possible, meaning we want to make our plugin a fully installable python module that your users will be able to
install directly via Python's standard package manager ``pip`` or alternatively via `OctoPrint's own plugin manager <https://github.com/OctoPrint/OctoPrint-PluginManager>`_.

So let's begin. First checkout the `Plugin Skeleton <https://github.com/OctoPrint/OctoPrint-PluginSkeleton>`_ and rename
the ``octoprint_skeleton`` folder to something better suited to our "Hello World" plugin::

   $ git clone https://github.com/OctoPrint/OctoPrint-PluginSkeleton.git OctoPrint-HelloWorld
   Cloning into 'OctoPrint-HelloWorld'...
   [...]
   $ cd OctoPrint-HelloWorld
   $ mv octoprint_skeleton octoprint_helloworld

Then edit the configuration in the ``setup.py`` file to mirror our own "Hello World" plugin. The configuration should
look something like this:

.. code-block:: python

   plugin_identifier = "helloworld"
   plugin_name = "OctoPrint-HelloWorld"
   plugin_version = "1.0"
   plugin_description = "A quick \"Hello World\" example plugin for OctoPrint"
   plugin_author = "You"
   plugin_author_email = "you@somewhere.net"
   plugin_url = "https://github.com/you/OctoPrint-HelloWorld"

Now all that's left to do is to move our ``helloworld.py`` into the ``octoprint_helloworld`` folder and renaming it to
``__init__.py``. Make sure to delete the copy under ``~/.octoprint/plugins`` in the process, including the `.pyc` file!

The plugin is now ready to be installed via ``python setup.py install``. However, since we are still
working on our plugin, it makes more sense to use ``python setup.py develop`` for now -- this way the plugin becomes
discoverable by OctoPrint, however we don't have to reinstall it after any changes we will still do::

   $ python setup.py develop
   running develop
   running egg_info
   creating OctoPrint_HelloWorld.egg-info
   [...]
   Finished processing dependencies for OctoPrint-HelloWorld==1.0

Restart OctoPrint. Your plugin should still be properly discovered and the log line should be printed::

   2015-01-27 13:43:34,134 - octoprint.server - INFO - Starting OctoPrint 1.2.0-dev-448-gd96e56e (devel branch)
   2015-01-27 13:43:34,134 - octoprint.plugin.core - INFO - Loading plugins from /home/pi/.octoprint/plugins, /home/pi/OctoPrint/src/octoprint/plugins and installed plugin packages...
   2015-01-27 13:43:34,818 - octoprint.plugin.core - INFO - Found 3 plugin(s): Hello World (1.0), CuraEngine (0.1), Discovery (0.1)
   [...]
   2015-01-27 13:43:38,997 - octoprint.plugins.helloworld - INFO - Hello World!

Looks like it still works!

Something is still a bit ugly though. Take a look into ``__init__.py`` and ``setup.py``. It seems like we have a bunch
of information now defined twice:

.. code-block:: python

   # __init__.py:
   __plugin_name__ = "Hello World"
   __plugin_version__ = "1.0"
   __plugin_description__ = "A quick \"Hello World\" example plugin for OctoPrint"

   # setup.py
   plugin_name = "OctoPrint-HelloWorld"
   plugin_version = "1.0"
   plugin_description = "A quick \"Hello World\" example plugin for OctoPrint"

The nice thing about our plugin now being a proper python package is that OctoPrint can and will access the metadata defined
within ``setup.py``! So, we don't really need to define all this data twice. Remove ``__plugin_name__``, ``__plugin_version__``
and ``__plugin_description__``:

.. code-block:: python

   # coding=utf-8
   from __future__ import absolute_import

   import octoprint.plugin

   class HelloWorldPlugin(octoprint.plugin.StartupPlugin):
       def on_after_startup(self):
           self._logger.info("Hello World!")

   __plugin_implementations__ = [HelloWorldPlugin()]

and restart OctoPrint::

   2015-01-27 13:46:33,786 - octoprint.plugin.core - INFO - Found 3 plugin(s): OctoPrint-HelloWorld (1.0), CuraEngine (0.1), Discovery (0.1)

Our "Hello World" Plugin still gets detected fine, but it's now listed under the same name it's installed under,
"OctoPrint-HelloWorld". That's a bit redundant and squashed, so we'll override that bit via ``__plugin_name__`` again:

.. code-block:: python
   :emphasize-lines: 10

   # coding=utf-8
   from __future__ import absolute_import

   import octoprint.plugin

   class HelloWorldPlugin(octoprint.plugin.StartupPlugin):
       def on_after_startup(self):
           self._logger.info("Hello World!")

   __plugin_name__ = "Hello World"
   __plugin_implementations__ = [HelloWorldPlugin()]


Restart OctoPrint again::

   2015-01-27 13:48:54,122 - octoprint.plugin.core - INFO - Found 3 plugin(s): Hello World (1.0), CuraEngine (0.1), Discovery (0.1)

Much better! You can override pretty much all of the metadata defined within ``setup.py`` from within your Plugin itself --
take a look at :ref:`the available control properties <sec-plugins-infrastructure-controlproperties>` for all available
overrides.

Following the README of the `Plugin Skeleton <https://github.com/OctoPrint/OctoPrint-PluginSkeleton>`_ you could now
already publish your plugin on Github and it would be directly installable by others using pip::

   pip install https://github.com/you/OctoPrint-HelloWorld/archive/master.zip

But let's add some more features instead.

.. _sec-plugins-gettingstarted-templates:

Frontend fun: How to add functionality to OctoPrint's web interface
-------------------------------------------------------------------

Outputting a log line upon server startup is all nice and well, but we want to greet not only the administrator of
our OctoPrint instance but actually everyone that opens OctoPrint in their browser. Therefore, we need to modify
OctoPrint's web interface itself.

We can do this using the :class:`TemplatePlugin` mixin. For now, let's start with a little "Hello World!" in OctoPrint's
navigation bar right at the top that links to the Wikipedia node about "Hello World" programs. For this we'll first
add the :class:`TemplatePlugin` to our ``HelloWorldPlugin`` class:

.. code-block:: python
   :emphasize-lines: 7

   # coding=utf-8
   from __future__ import absolute_import

   import octoprint.plugin

   class HelloWorldPlugin(octoprint.plugin.StartupPlugin,
                          octoprint.plugin.TemplatePlugin):
       def on_after_startup(self):
           self._logger.info("Hello World!")

   __plugin_name__ = "Hello World"
   __plugin_implementations__ = [HelloWorldPlugin()]

Next, we'll create a sub folder ``templates`` underneath our ``octoprint_helloworld`` folder, and within that a file
``helloworld_navbar.jinja2`` like so:

.. code-block:: html

   <a href="https://en.wikipedia.org/wiki/Hello_world">Hello World!</a>

Our plugin's directory structure should now look like this::

   octoprint_helloworld/
       templates/
           helloworld_navbar.jinja2
       __init__.py
   README.md
   requirements.txt
   setup.py

Restart OctoPrint and open the web interface in your browser (make sure to clear your browser's cache!).

.. _fig-plugins-gettingstarted-helloworld_navbar:
.. figure:: ../images/plugins_gettingstarted_helloworld_navbar.png
   :align: center
   :alt: Our "Hello World" navigation bar element in action

Now look at that!

.. _sec-plugins-gettingstarted-settings:

Settings Galore: How to make parts of your plugin user adjustable
-----------------------------------------------------------------

Remember that Wikipedia link we added to our little link in the navigation bar? It links to the english Wikipedia. But
what if we want to allow our users to adjust that according to their wishes, e.g. to link to the german language node
about "Hello World" programs instead?

To allow your users to customized the behaviour of your plugin you'll need to implement the :class:`~octoprint.plugin.SettingsPlugin`
mixin and override it's :func:`~octoprint.plugin.SettingsPlugin.get_settings_defaults` method. We'll save the URL to
inject into the link under the key ``url`` in our plugin's settings and set it to the old value by default. We'll therefore
return just a single key in our default settings dictionary. To be able to quickly see if we've done that right we'll
extend our little startup message to also log the current setting to the console. We can access that via ``self._settings``,
which is a little settings manager OctoPrint conveniently injects into our Plugin when we include the :class:`~octoprint.plugin.SettingsPlugin`
mixin.

Let's take a look at how all that would look in our plugin's ``__init__.py``:

.. code-block:: python
   :emphasize-lines: 8, 10, 12-13

   # coding=utf-8
   from __future__ import absolute_import

   import octoprint.plugin

   class HelloWorldPlugin(octoprint.plugin.StartupPlugin,
                          octoprint.plugin.TemplatePlugin,
                          octoprint.plugin.SettingsPlugin):
       def on_after_startup(self):
           self._logger.info("Hello World! (more: %s)" % self._settings.get(["url"]))

       def get_settings_defaults(self):
           return dict(url="https://en.wikipedia.org/wiki/Hello_world")

   __plugin_name__ = "Hello World"
   __plugin_implementations__ = [HelloWorldPlugin()]

Restart OctoPrint. You should see something like this::

   2015-01-30 11:41:06,058 - octoprint.plugins.helloworld - INFO - Hello World! (more: https://en.wikipedia.org/wiki/Hello_world)

So far so good. But how do we now get that value into our template? We have two options, the
static one using so called template variables and a dynamic one which retrieves that data from the backend and binds it
into the template using `Knockout data bindings <http://knockoutjs.com/documentation/introduction.html>`_. First let's
take a look at the static version using template variables. We already have the :class:`~octoprint.plugin.TemplatePlugin`
mixin included in our plugin, we just need to override its method :func:`~octoprint.plugin.TemplatePlugin.get_template_vars`
to add our URL as a template variable.

Adjust your plugin's ``__init__.py`` like this:

.. code-block:: python
   :emphasize-lines: 15-16

   # coding=utf-8
   from __future__ import absolute_import

   import octoprint.plugin

   class HelloWorldPlugin(octoprint.plugin.StartupPlugin,
                          octoprint.plugin.TemplatePlugin,
                          octoprint.plugin.SettingsPlugin):
       def on_after_startup(self):
           self._logger.info("Hello World! (more: %s)" % self._settings.get(["url"]))

       def get_settings_defaults(self):
           return dict(url="https://en.wikipedia.org/wiki/Hello_world")

       def get_template_vars(self):
           return dict(url=self._settings.get(["url"]))

   __plugin_name__ = "Hello World"
   __plugin_implementations__ = [HelloWorldPlugin()]

Also adjust your plugin's ``templates/helloworld_navbar.jinja2`` like this:

.. code-block:: html

   <a href="{{ plugin_helloworld_url|escape }}">Hello World!</a>

OctoPrint injects the template variables that your plugin defines prefixed with ``plugin_<plugin identifier>_`` into
the template renderer, so your ``url`` got turned into ``plugin_helloworld_url`` which you can now use as a simple
`Jinja2 Variable <http://jinja.pocoo.org/docs/dev/templates/#variables>`_ in your plugin's template.

Restart OctoPrint and shift-reload the page in your browser (to make sure you really get a fresh copy). The link should
still work and point to the URL we defined as default.

Let's change the URL! Open up your OctoPrint instance's ``config.yaml`` file and add the following to it (if a ``plugins``
section doesn't yet exist in the file, create it):

.. code-block:: yaml
   :emphasize-lines: 3-4

   # [...]
   plugins:
     helloworld:
       url: https://de.wikipedia.org/wiki/Hallo-Welt-Programm
   # [...]

Restart OctoPrint. Not only should the URL displayed in the log file have changed, but also the link should now (after
a proper shift-reload) point to the german Wikipedia node about "Hello World" programs::

   2015-01-30 11:47:18,634 - octoprint.plugins.helloworld - INFO - Hello World! (more: https://de.wikipedia.org/wiki/Hallo-Welt-Programm)

Nice! But not very user friendly. We don't have any way yet to edit the URL from within OctoPrint and have to restart
the server and reload the page every time we want a value change to take effect. Let's try adding a little settings dialog
for our plugin in which we can edit the URL and take any changes take immediate effect.

First of all, we'll create the settings dialog. You might already have guessed that we'll need another template for that.
So in your plugin's ``templates`` folder create a new file ``helloworld_settings.jinja2`` and put the following content
into it:

.. code-block:: html

   <form class="form-horizontal">
       <div class="control-group">
           <label class="control-label">{{ _('URL') }}</label>
           <div class="controls">
               <input type="text" class="input-block-level" data-bind="value: settings.plugins.helloworld.url">
           </div>
       </div>
   </form>

Note how we access our plugin's property via ``settings.plugins.helloworld.url``. The ``settings`` observable is made
available in the ``SettingsViewModel`` and holds the exact data structure returned from the server for all of
OctoPrint's settings. Accessing plugin settings hence works by following the path under which they are stored in
OctoPrint's internal settings data model (made public via the ``config.yaml``), ``plugins.<plugin identifier>.<configuration key>``.
We'll bind our own settings dialog to the existing ``SettingsViewModel``, so this will be the way we'll access our
property.

Now adjust your ``templates/helloworld_navbar.jinja2`` file to use a ``data-bind`` attribute to set the value from the
settings view model into the ``href`` attribute of the link tag:

.. code-block:: html

   <a href="#" data-bind="attr: {href: settings.settings.plugins.helloworld.url}">Hello World!</a>

You might have noticed the quite ugly way to access our plugin's ``url`` property here: ``settings.settings.plugins.helloworld.url``.
The reason for this is that we'll make our plugin use the existing ``NavigationViewModel`` which holds the
``SettingsViewModel`` as a property called ``settings``. So to get to the ``settings`` property of the ``SettingsViewModel``
from the ``NavigationViewModel``, we'll need to first "switch" to the ``SettingsViewModel`` using its property name. Hence
the ugly access string.

If you were now to restart OctoPrint and reload the web interface, you'll get the settings dialog placed just fine
in OctoPrint's settings, and the link would also still show up in the navigation bar, but both the input field of the
settings dialog as well as the link's ``href`` attribute would not show our link. The reason for this is that OctoPrint
by default assumes that you'll want to bind your own view models to your templates and hence "unbinds" the included
templates from the templates that are in place at the injected location already. In order to tell OctoPrint to please
don't do this here (since we *do* want to use both ``NavigationViewModel`` and ``SettingsViewModel``), we'll need to
override the default template configuration using the :class:`~octoprint.plugin.TemplatePlugin`s
:func:`~octoprint.plugin.TemplatePlugin.get_template_configs` method. We'll tell OctoPrint to use no custom bindings
for both our ``navbar`` and our ``settings`` plugin. We'll also remove the override of :func:`octoprint.plugin.TemplatePlugin.get_template_vars`
again since we don't use that anymore:

.. code-block:: python
   :emphasize-lines: 15-19

   # coding=utf-8
   from __future__ import absolute_import

   import octoprint.plugin

   class HelloWorldPlugin(octoprint.plugin.StartupPlugin,
                          octoprint.plugin.TemplatePlugin,
                          octoprint.plugin.SettingsPlugin):
   def on_after_startup(self):
       self._logger.info("Hello World! (more: %s)" % self._settings.get(["url"]))

   def get_settings_defaults(self):
       return dict(url="https://en.wikipedia.org/wiki/Hello_world")

   def get_template_configs(self):
       return [
           dict(type="navbar", custom_bindings=False),
           dict(type="settings", custom_bindings=False)
       ]

   __plugin_name__ = "Hello World"
   __plugin_implementations__ = [HelloWorldPlugin()]

Restart OctoPrint and shift-reload your browser. Your link in the navigation bar should still point to the URL we
defined in ``config.yaml`` earlier. Open the "Settings" and click on the new "Hello World" entry that shows up under
"Plugins".

.. _fig-plugins-gettingstarted-helloworld_settings:
.. figure:: ../images/plugins_gettingstarted_helloworld_settings.png
   :align: center
   :alt: Our "Hello World" navigation bar element in action

Nice! Edit the value, then click "Save". Your link in the navigation bar should now have been updated as well.

.. note::

   The way we've done our data binding and how OctoPrint currently works, your link's target will update immediately
   when you update the value in the settings dialog. Even if you click Cancel instead of Save, the change will still
   be reflected in the UI but will be overwritten again by the stored data upon a reload. This is caused by OctoPrint
   not storing a copy of the settings data while it is being edited, which might be changed in the future to
   prevent this unexpected behaviour from occurring.

Congratulations, you've just made your Plugin configurable :)