---+ Package =TWiki::Plugins=

This module defines the singleton object that handles Plugins
loading, initialization and execution.

This class uses Chain of Responsibility (GOF) pattern to dispatch
handler calls to registered plugins.


%TOC%

Note that as of version 1.026 of this module, TWiki internal
methods are _no longer available_ to plugins. Any calls to
TWiki internal methods must be replaced by calls via the
=$SESSION= object in this package, or via the Func package.
For example, the call:

=my $pref = TWiki::getPreferencesValue('URGH');=

should be replaced with

=my $pref = TWiki::Func::getPreferencesValue('URGH');=

and the call

=my $t = TWiki::writeWarning($message);=

should be replaced with

=my $pref = $TWiki::Plugins::SESSION->writeWarning($message);=

Methods in other modules such as Store must be accessed through
the relevant TWiki sub-object, for example

=TWiki::Store::saveTopic(...)=

should be replaced with

=$TWiki::Plugins::SESSION->{store}->saveTopic(...)=

Note that calling TWiki internal methods is very very bad practice,
and should be avoided wherever practical.

The developers of TWiki reserve the right to change internal
methods without warning, unless those methods are clearly
marked as PUBLIC. PUBLIC methods are part of the core specification
of a module and can be trusted.


---++ PUBLIC constant $VERSION

This is the version number of the plugins package. Use it for checking
if you have a recent enough version.

---++ PUBLIC $SESSION

This is a reference to the TWiki session object. It can be used in
plugins to get at the methods of the TWiki kernel.

You are _highly_ recommended to only use the methods in the
[[TWikiFuncDotPm][Func]] interface, unless you have no other choice,
as kernel methods may change between TWiki releases.


---++ ClassMethod *new* <tt>($session)</tt>

Construct new singleton plugins collection object. The object is a
container for a list of plugins and the handlers registered by the plugins.
The plugins and the handlers are carefully ordered.



---++ ObjectMethod *finish* <tt>()</tt>
Break circular references.



---++ ObjectMethod *load* <tt>($allDisabled) -> $loginName</tt>

Find all active plugins, and invoke the early initialisation.
Has to be done _after_ prefs are read.

Returns the user returned by the last =initializeUserHandler= to be
called.

If allDisabled is set, no plugin handlers will be called.



---++ ObjectMethod *settings* <tt>()</tt>

Push plugin settings onto preference stack



---++ ObjectMethod *enable* <tt>()</tt>

Initialisation that is done after the user is known.



---++ ObjectMethod *getPluginVersion* <tt>() -> $number</tt>

Returns the $TWiki::Plugins::VERSION number if no parameter is specified,
else returns the version number of a named Plugin. If the Plugin cannot
be found or is not active, 0 is returned.



---++ ObjectMethod *addListener* <tt>($command,$handler)</tt>

   * =$command= - name of the event
   * =$handler= - the handler object.

Add a listener to the end of the list of registered listeners for this event.
The listener must implement =invoke($command,...)=, which will be triggered
when the event is to be processed.



---++ ObjectMethod *dispatch* <tt>($handlerName,...)</tt>
Dispatch the given handler, passing on ... in the parameter vector



---++ ObjectMethod *haveHandlerFor* <tt>($handlerName) -> $boolean</tt>

   * =$handlerName= - name of the handler e.g. preRenderingHandler
Return: true if at least one plugin has registered a handler of
this type.