A FEW NOTES ON THE PLUGIN ARCHITECTURE
======================================

The plugin architecture of SquirrelMail is designed to make it
possible to add new features without having to patch SquirrelMail
itself. At the moment the plugin part of SquirrelMail should be
considered "alpha" or "beta" quality code.

Until the functionality and code is more stable, be prepared for
plugins to suddenly stop working.

Functionality like password changing, displaying ads and calendars
should be possible to add as plugins.


The idea
--------

The idea is to be able to run random code at given places in the
SquirrelMail code. This random code should then be able to do whatever
needed to enhance the functionality of SquirrelMail. The places where
code can be executed are called "hooks".

There are some limitations in what these hooks can do. It is difficult
to use them to change the layout and to change functionality that
already is in SquirrelMail.

Some way for the plugins to interact with the help subsystem and
translations will be provided.


The implementation
------------------

In the main SquirrelMail files the file functions/plugin.php. In
places where hooks are made available they are executed by calling the
function do_hook("hookname").

The do_hook traverses the array $squirrelmail_plugin_hooks["hookname"]
and executes all the functions that are named in that array.

A plugin must reside in a subdirectory in the plugins/ directory. The
name of the subdirectory is considered the name of the plugin.

To start using a plugin, its name must be added to the $plugins array
in config.php like this:

  $plugins[0] = "plugin_name";

When a plugin is registered the file plugins/plugin_name/setup.php is
included and the function squirrelmail_plugin_init_plugin_name is
called with no parameters.


Writing plugins
---------------

A plugin must consist of at least a file called setup.php. All other
files the plugin consist of should also be in the plugin directory.

The function squirrelmail_plugin_init_plugin_name is called to
initalize a plugin. This function could look something like this:

function squirrelmail_plugin_init_demo () {
  global $squirrelmail_plugin_hooks;

  $squirrelmail_plugin_hooks["generic_header"]["demo"] = "plugin_demo_header";
  $squirrelmail_plugin_hooks["menuline"]["demo"] = "plugin_demo_menuline";
}

Note that the SquirrelMail files assume that all other SquirrelMail
files are available as ../directory/file. This means that if some file
in the plugin directory is requested, it must do a chdir("..") before
including any of the standard SquirrelMail files.