NAME
    POE::Component::Pluggable - A base class for creating plugin-enabled
    POE Components.
VERSION
    version 1.28
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(POE::Component::Pluggable);
         use POE;
         use POE::Component::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 POE::Component::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
    POE::Component::Pluggable is a base class for creating plugin enabled
    POE Components. It is a generic port of POE::Component::IRC's plugin
    system.
    If your component dispatches events to registered POE sessions, then
    POE::Component::Pluggable may be a good fit for you.
    Basic use would involve subclassing POE::Component::Pluggable, then
    overriding _pluggable_event() and inserting _pluggable_process()
    wherever you dispatch events from.
    Users of your component can then load plugins using the plugin methods
    provided to handle events generated by the component.
    You may also use plugin style handlers within your component 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 POE::Component::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 {
         # stuff
     
         return 1 if $self->_pluggable_process($type, $event, \(@args)) == PLUGIN_EAT_ALL;
     
         # dispatch event to interested sessions.
     }
    This example demonstrates event arguments being passed as scalar refs
    to the plugin system. This enables plugins to mangle the arguments if
    necessary.
 _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 POE::Component::Pluggable gives your object the following
    public methods:
 pipeline
    Returns the POE::Component::Pluggable::Pipeline object.
 plugin_add
    Accepts two arguments:
     The alias for the plugin
     The actual plugin object
    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
    POE::Component::Pluggable object.
    This method goes through the pipeline's push() method, which will call
    $plugin-plugin_register($pluggable)>.
    Returns the number of plugins now in the pipeline if plugin was
    initialized, undef/an empty list if not.
 plugin_del
    Accepts one argument:
     The alias for the plugin or the plugin object itself
    This method goes through the pipeline's remove() method, which will
    call $plugin-plugin_unregister($pluggable)>.
    Returns the plugin object if the plugin was removed, undef/an empty
    list if not.
 plugin_get
    Accepts one argument:
     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 POE::Component::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
    POE::Component::Pluggable::Constants. You could provide your own as
    long as the values match up, though.
TODO
    Better documentation >:]
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
    POE::Component::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.
AUTHORS
      * Chris Williams <chris@bingosnet.co.uk>
      * Apocalypse <perl@0ne.us>
      * Hinrik Örn Sigurðsson
      * Jeff Pinyan
COPYRIGHT AND LICENSE
    This software is copyright (c) 2017 by Chris Williams.
    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.