NAME
    Object::Pluggable - A base class for creating plugin-enabled objects

SYNOPSIS
     # A simple POE Component that sends ping events to registered sessions
     # and plugins every second.

     {
         package SimplePoCo;

         use strict;
         use warnings;
         use base qw(Object::Pluggable);
         use POE;
         use Object::Pluggable::Constants qw(:ALL);

         sub spawn {
             my ($package, %opts) = @_;
             my $self = bless \%opts, $package;

             $self->_pluggable_init(
                 prefix => 'simplepoco_',
                 types  => [qw(EXAMPLE)],
                 debug  => 1,
             );

             POE::Session->create(
                 object_states => [
                     $self => { shutdown => '_shutdown' },
                     $self => [qw(_send_ping _start register unregister __send_event)],
                 ],
             );

             return $self;
         }

         sub shutdown {
             my ($self) = @_;
             $poe_kernel->post($self->{session_id}, 'shutdown');
         }

         sub _pluggable_event {
             my ($self) = @_;
             $poe_kernel->post($self->{session_id}, '__send_event', @_);
         }

         sub _start {
             my ($kernel, $self) = @_[KERNEL, OBJECT];
             $self->{session_id} = $_[SESSION]->ID();

             if ($self->{alias}) {
                 $kernel->alias_set($self->{alias});
             }
             else {
                 $kernel->refcount_increment($self->{session_id}, __PACKAGE__);
             }

             $kernel->delay(_send_ping => $self->{time} || 300);
             return;
         }

         sub _shutdown {
              my ($kernel, $self) = @_[KERNEL, OBJECT];

              $self->_pluggable_destroy();
              $kernel->alarm_remove_all();
              $kernel->alias_remove($_) for $kernel->alias_list();
              $kernel->refcount_decrement($self->{session_id}, __PACKAGE__) if !$self->{alias};
              $kernel->refcount_decrement($_, __PACKAGE__) for keys %{ $self->{sessions} };

              return;
         }

         sub register {
             my ($kernel, $sender, $self) = @_[KERNEL, SENDER, OBJECT];
             my $sender_id = $sender->ID();
             $self->{sessions}->{$sender_id}++;

             if ($self->{sessions}->{$sender_id} == 1) { 
                 $kernel->refcount_increment($sender_id, __PACKAGE__);
                 $kernel->yield(__send_event => 'simplepoco_registered', $sender_id);
             }

             return;
         }

         sub unregister {
             my ($kernel, $sender, $self) = @_[KERNEL, SENDER, OBJECT];
             my $sender_id = $sender->ID();
             my $record = delete $self->{sessions}->{$sender_id};

             if ($record) {
                 $kernel->refcount_decrement($sender_id, __PACKAGE__);
                 $kernel->yield(__send_event => 'simplepoco_unregistered', $sender_id);
             }

             return;
         }
  
         sub __send_event {
             my ($kernel, $self, $event, @args) = @_[KERNEL, OBJECT, ARG0..$#_];

             return 1 if $self->_pluggable_process(EXAMPLE => $event, \@args) == PLUGIN_EAT_ALL;
             $kernel->post($_, $event, @args) for keys %{ $self->{sessions} };
         }

         sub _send_ping {
             my ($kernel, $self) = @_[KERNEL, OBJECT];

             $kernel->yield(__send_event => 'simplepoco_ping', 'Wake up sleepy');
             $kernel->delay(_send_ping => $self->{time} || 1);
             return;
         }
     }

     {
         package SimplePoCo::Plugin;
         use strict;
         use warnings;
         use Object::Pluggable::Constants qw(:ALL);

         sub new {
             my $package = shift;
             return bless { @_ }, $package;
         }

         sub plugin_register {
             my ($self, $pluggable) = splice @_, 0, 2;
             print "Plugin added\n";
             $pluggable->plugin_register($self, 'EXAMPLE', 'all');
             return 1;
         }

         sub plugin_unregister {
             print "Plugin removed\n";
             return 1;
         }

         sub EXAMPLE_ping {
             my ($self, $pluggable) = splice @_, 0, 2;
             my $text = ${ $_[0] };
             print "Plugin got '$text'\n";
             return PLUGIN_EAT_NONE;
         }
     }

     use strict;
     use warnings;
     use POE;

     my $pluggable = SimplePoCo->spawn(
         alias => 'pluggable',
         time  => 1,
     );

     POE::Session->create(
         package_states => [
             main => [qw(_start simplepoco_registered simplepoco_ping)],
         ],
     );

     $poe_kernel->run();

     sub _start {
         my $kernel = $_[KERNEL];
         $kernel->post(pluggable => 'register');
         return;
     }

     sub simplepoco_registered {
         print "Main program registered for events\n";
         my $plugin = SimplePoCo::Plugin->new();
         $pluggable->plugin_add('TestPlugin', $plugin);
         return;
     }

     sub simplepoco_ping {
         my ($heap, $text) = @_[HEAP, ARG0];
         print "Main program got '$text'\n";
         $heap->{got_ping}++;
         $pluggable->shutdown() if $heap->{got_ping} == 3;
         return;
     }

DESCRIPTION
    Object::Pluggable is a base class for creating plugin enabled objects.
    It is a generic port of POE::Component::IRC's plugin system.

    If your object dispatches events to listeners, then Object::Pluggable
    may be a good fit for you.

    Basic use would involve subclassing Object::Pluggable, then overriding
    "_pluggable_event()" and inserting "_pluggable_process()" wherever you
    dispatch events from.

    Users of your object can then load plugins using the plugin methods
    provided to handle events generated by the object.

    You may also use plugin style handlers within your object as
    "_pluggable_process()" will attempt to process any events with local
    method calls first. The return value of these handlers has the same
    significance as the return value of 'normal' plugin handlers.

PRIVATE METHODS
    Subclassing Object::Pluggable gives your object the following 'private'
    methods:

  "_pluggable_init"
    This should be called on your object after initialisation, but before
    you want to start processing plugins. It accepts a number of
    argument/value pairs:

     'types', an arrayref of the types of events that your poco will support,
              OR a hashref with the event types as keys and their abbrevations
              (used as plugin event method prefixes) as values. This argument is
              mandatory.

     'prefix', the prefix for your events (default: 'pluggable_');
     'reg_prefix', the prefix for the register()/unregister() plugin methods 
                   (default: 'plugin_');
     'debug', a boolean, if true, will cause a warning to be printed every time a
              plugin call fails.

    Notes: 'prefix' should probably end with a '_'. The types specify the
    prefixes for plugin handlers. You can specify as many different types as
    you require.

  "_pluggable_destroy"
    This should be called from any shutdown handler that your poco has. The
    method unloads any loaded plugins.

  "_pluggable_process"
    This should be called before events are dispatched to interested
    sessions. This gives pluggable a chance to discard events if requested
    to by a plugin.

    The first argument is a type, as specified to "_pluggable_init()".

     sub _dispatch {
         my ($self, $event, $type, @args) = @_;

         # stuff

         my $type = ...

         return 1 if $self->_pluggable_process($type, $event, \@args)) == PLUGIN_EAT_ALL;

         # dispatch event to interested sessions.
     }

    A reference to the argument array is passed. This allows the plugin
    system to mangle the arguments or even add new ones.

  "_pluggable_event"
    This method should be overridden in your class so that pipeline can
    dispatch events through your event dispatcher. Pipeline sends a prefixed
    'plugin_add' and 'plugin_del' event whenever plugins are added or
    removed, respectively. A prefixed 'plugin_error' event will be sent if a
    plugin a) raises an exception, b) fails to return a true value from its
    register/unregister methods, or c) fails to return a valid EAT constant
    from a handler.

     sub _pluggable_event {
         my $self = shift;
         $poe_kernel->post($self->{session_id}, '__send_event', @_);
     }

    There is an example of this in the SYNOPSIS.

PUBLIC METHODS
    Subclassing Object::Pluggable gives your object the following public
    methods:

  "pipeline"
    Returns the Object::Pluggable::Pipeline object.

  "plugin_add"
    Accepts two arguments:

     The alias for the plugin
     The actual plugin object
     Any number of extra arguments

    The alias is there for the user to refer to it, as it is possible to
    have multiple plugins of the same kind active in one Object::Pluggable
    object.

    This method goes through the pipeline's "push()" method, which will call
    "$plugin->plugin_register($pluggable, @args)".

    Returns the number of plugins now in the pipeline if plugin was
    initialized, "undef"/an empty list if not.

  "plugin_del"
    Accepts the following arguments:

     The alias for the plugin or the plugin object itself
     Any number of extra arguments

    This method goes through the pipeline's "remove()" method, which will
    call "$plugin->plugin_unregister($pluggable, @args)".

    Returns the plugin object if the plugin was removed, "undef"/an empty
    list if not.

  "plugin_get"
    Accepts the following arguments:

     The alias for the plugin

    This method goes through the pipeline's "get()" method.

    Returns the plugin object if it was found, "undef"/an empty list if not.

  "plugin_list"
    Takes no arguments.

    Returns a hashref of plugin objects, keyed on alias, or an empty list if
    there are no plugins loaded.

  "plugin_order"
    Takes no arguments.

    Returns an arrayref of plugin objects, in the order which they are
    encountered in the pipeline.

  "plugin_register"
    Accepts the following arguments:

     The plugin object
     The type of the hook (the hook types are specified with _pluggable_init()'s 'types')
     The event name[s] to watch

    The event names can be as many as possible, or an arrayref. They
    correspond to the prefixed events and naturally, arbitrary events too.

    You do not need to supply events with the prefix in front of them, just
    the names.

    It is possible to register for all events by specifying 'all' as an
    event.

    Returns 1 if everything checked out fine, "undef"/an empty list if
    something is seriously wrong.

  "plugin_unregister"
    Accepts the following arguments:

     The plugin object
     The type of the hook (the hook types are specified with _pluggable_init()'s 'types')
     The event name[s] to unwatch

    The event names can be as many as possible, or an arrayref. They
    correspond to the prefixed events and naturally, arbitrary events too.

    You do not need to supply events with the prefix in front of them, just
    the names.

    It is possible to register for all events by specifying 'all' as an
    event.

    Returns 1 if all the event name[s] was unregistered, undef if some was
    not found.

PLUGINS
    The basic anatomy of a pluggable plugin is:

     # Import the constants, of course you could provide your own 
     # constants as long as they map correctly.
     use Object::Pluggable::Constants qw( :ALL );

     # Our constructor
     sub new {
         ...
     }

     # Required entry point for pluggable plugins
     sub plugin_register {
         my($self, $pluggable) = @_;

         # Register events we are interested in
         $pluggable->plugin_register($self, 'SERVER', qw(something whatever));

         # Return success
         return 1;
     }

     # Required exit point for pluggable
     sub plugin_unregister {
         my($self, $pluggable) = @_;

         # Pluggable will automatically unregister events for the plugin

         # Do some cleanup...

         # Return success
         return 1;
     }

     sub _default {
         my($self, $pluggable, $event) = splice @_, 0, 3;

         print "Default called for $event\n";

         # Return an exit code
         return PLUGIN_EAT_NONE;
     }

    As shown in the example above, a plugin's "_default" subroutine (if
    present) is called if the plugin receives an event for which it has no
    handler.

    The special exit code CONSTANTS are documented in
    Object::Pluggable::Constants. You could provide your own as long as the
    values match up, though.

TODO
    Better documentation >:]

AUTHOR
    Chris 'BinGOs' Williams <chris@bingosnet.co.uk>

LICENSE
    Copyright "(c)" Chris Williams, Apocalypse, Hinrik Örn Sigurðsson and
    Jeff Pinyan

    This module may be used, modified, and distributed under the same terms
    as Perl itself. Please see the license that came with your Perl
    distribution for details.

KUDOS
    APOCAL for writing the original POE::Component::IRC plugin system.

    japhy for writing POE::Component::IRC::Pipeline which improved on it.

    All the happy chappies who have contributed to POE::Component::IRC over
    the years (yes, it has been years) refining and tweaking the plugin
    system.

    The initial idea was heavily borrowed from X-Chat, BIG thanks go out to
    the genius that came up with the EAT_* system :)

SEE ALSO
    POE::Component::IRC

    Object::Pluggable::Pipeline

    Both POE::Component::Client::NNTP and POE::Component::Server::NNTP use
    this module as a base, examination of their source may yield further
    understanding.