README

# Mythbuntu Control Panel (MCP)
# MCP source code: https://github.com/mythcp/mythbuntu-control-panel

See www.mythtv.org/wiki/Mythbuntu_Control_Panel for installation and usage 
instructions.

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-- What's this wonderful application? --
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This application is based on and contains mostly the same code as found in 
Mythbuntu Control Centre.  MCC was mainly used as part of the Linux distribution
Mythbuntu, and it was installed when installing the operating system.  MCP is 
installed after installing Ubuntu, and it is used to install MythTV and perform 
MythTV related administration tasks.  It aims to minimize the need to perform 
tasks using the command line to configure the system.

MCP retains MCC's "fully pluggable" architecture.  This means that all
functionality is actually configurable by the plugins that get installed
in the standard location rather than with the core application.  This allows
developers to create their own sets of plugins to be used with MCP.
 
MCP is community maintained and not endorsed by Canonical.

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-- Architecture Defined --
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MCP (aka Mythbuntu Control Panel) is a client/server application with the server
and client intended to run on the same machine.  The two components contact one 
another via dbus with authentication from PolicyKit.  This allows the frontend 
and all GUI functionality to run as a userspace process.  The backend is spawned
using dbus service activation as necessary.  When inactive for a pre-defined 
time, the backend will stop itself and only respawn when requested by the
frontend.

The intention behind this architecture definition is to abstract the developer 
from having to spend time re-inventing processes that are likely already in use 
by other MCP plugins.

The core MCP application provides hooks available for all plugins to use. 
Optionally, these hooks can define post install actions or apt related actions.

Functionally, the frontend and backend processes will both import the python 
plugin and initialize the class for each process.  The frontend also calls the 
GTK functions, whereas the backend only calls upon two backend functions.

All plugins are stored in /usr/share/mythbuntu/plugins/{python,ui}.  Each 
plugin requires a python source file and a GtkBuilder UI file.  The details for 
how these need to be implemented are defined below.

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-- Writing a plugin --
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The plugins included with MCP can be reviewed and used as examples when creating
a new plugin.  MCP can stated using a custom plugin path by running:

 # mythbuntu-control-panel --plugin-root-path=/path/to/plugins/{python,ui}

This launches the control panel with only plugins found in that plugin-root-
path.  This is helpful for development so that you know your plugin is not
causing problems early on.

It's best to develop the frontend of a plugin before the backend.  Start out 
using the Glade Development tool, glade-3.

Opening up glade-3, a few items should be apparent.
 - The plugin's file name needs to match the top most non window widget of the 
   plugin.  This is what is used to key off what file the plugin loads for the 
   GUI.
 - The goal is to use the minimum amount of space.  Try not to add too much text
   as the control panel's minimum size is determined by the max size of a 
   plugin.
 - Use alignment boxes to keep widgets from the edges.  They look much better 
   this way.

After finishing off the GUI, be sure to take note of any widgets that you will 
need to be keying off in the python file.

Open up the python file in your favorite editor.  We'll discuss the
elements that are required for the frontend of the plugin first.

--Frontend--

A frontend plugin will always inherit from the class MCPPlugin.  By doing so, a 
variety of methods will be available for the plugin.  You'll need to override 
these methods at a minimum to ensure proper functionality:
 - __init__
 - captureState
 - applyStateToGUI
 - compareState

In __init__ you need to define a dictionary with the items 'name', 'icon' and 
'ui'.  After building this dictionary, you need to call the parent MCPPlugin 
__init__ with that dictionary.
 - 'name' is the name of the plugin on the right side of the MCP UI
 - 'icon' is the icon that will show up on the right side of the UI
 - 'ui' is the name of the GtkBuilder file to be loaded (sans .ui)

captureState captures the state of all elements on the system.  It is 
intentionally unpaired with applyStateToGUI and compareState because MCP may 
call these at any time.  It's best to store any information determined about the 
installed system in a dictionary for later use.
 - query_installed can be used for querying packaged applications
 - you can import any python packages and use them as well

applyStateToGUI will override any currently set GUI elements with things that 
were determined in captureState.

compareState will compare that dictionary with the currently set GUI elements to
determine what's changed.
 - If it is determined that the page needs more activity before being "done", 
   self._incomplete can be set to True.
 - It's important to call MCPPlugin.clearParentState(self) in this function so 
   that the frontend is in a standard state.

The following functions can be used to record what the backend needs:
 - _markInstall: marks a package to be installed
 - _markRemove: marks a package to be removed
 - _markReconfigureUser: marks a scripted change to be done as a user
 - _markReconfigureRoot: marks a scripted change to be done by root
 - _markUpdatePackageList : requests a package list update after completion
 - _markUnauthenticatedPackages : requests that an unauthenticated package be 
   installed

Callbacks can also be used, but generally the model is that changes shouldn't 
occur until after the frontend calls apply.

--Backend--

If you are only making package installs or removals, you don't need to define 
any more functionality to the plugin.

If you need to represent changes that aren't part of the package 
(scriptedchanges), then you need to define two more methods:
 - root_scripted_changes
 - user_scripted_changes
Both methods have an argument of a dictionary of items to change.

The exact same python source file is loaded into the backend process when 
spawned if necessary, so be cognizant that you shouldn't do any GTK 
initialization in __init__ or the backend will fail.

Generally you want to walk through the dictionary argument for both cases 
through a for loop as more than one item can be sent at a time.

Running 'dpkg-reconfigure PACKAGE' is OK in this section, but be sure to set the
env to 'noninteractive' and instead make the changes in flat text files that can
be read by the maintainer scripts of that package.

Try to use subprocess.call rather than os.system so the return status can be 
determined.

If you are running an application that may take a long time in your processing 
functions, you might want to use emit_progress which will update the GUI with 
the latest status.

To assist in debugging, you may consider importing the 'logging' module.  
logging.warning('message') will always show up in the backend log logging.debug
('message') will show up when the backend is spawned with --debug.

--Packaging--
When your plugin is stable, you can start moving it into the system location of 
/usr/share/mythbuntu/plugins.  This means that the standard invokation of 
mythbuntu-control-panel will initialize your plugin along with the others on the
system.  This adds a new set of variables, particularly if you have any name 
clashes.  Be sure to test like this before issuing your plugin to make sure 
there are no blatant problems.