package Class::Trigger;
use 5.008_001;
use strict;
use vars qw($VERSION);
$VERSION = "0.15";

use Carp ();

my (%Triggers, %TriggerPoints);
my %Fetch_All_Triggers_Cache;

sub import {
    my $class = shift;
    my $pkg = caller(0);

    $TriggerPoints{$pkg} = { map { $_ => 1 } @_ } if @_;

    # export mixin methods
    no strict 'refs';
    my @methods = qw(add_trigger call_trigger last_trigger_results);
    *{"$pkg\::$_"} = \&{$_} for @methods;

sub add_trigger {
    my $proto = shift;

    my $triggers = __fetch_triggers($proto);

    my %params = @_;
    my @values = values %params;
    if (@_ > 2 && (grep { ref && ref eq 'CODE' } @values) == @values) {
        Carp::croak "mutiple trigger registration in one add_trigger() call is deprecated.";

    if ($#_ == 1 && ref($_[1]) eq 'CODE') {
        @_ = (name => $_[0], callback => $_[1]);

    my %args = ( name => undef, callback => undef, abortable => undef, @_ );
    my $when = $args{'name'};
    my $code = $args{'callback'};
    my $abortable = $args{'abortable'};
    __validate_triggerpoint( $proto, $when );
    Carp::croak('add_trigger() needs coderef') unless ref($code) eq 'CODE';
    push @{ $triggers->{$when} }, [ $code, $abortable ];

    # Clear the cache when class triggers are added.  Because triggers are 
    # inherited adding a trigger to one class may effect others.  Simplest
    # thing to do is to clear the whole thing.
    %Fetch_All_Triggers_Cache = () unless ref $proto;


sub last_trigger_results {
    my $self = shift;
    my $result_store = ref($self) ? $self : ${Class::Trigger::_trigger_results}->{$self};
    return $result_store->{'_class_trigger_results'};

sub call_trigger {
    my $self = shift;
    my $when = shift;

    my @return;

    my $result_store = ref($self) ? $self : ${Class::Trigger::_trigger_results}->{$self};

    $result_store->{'_class_trigger_results'} = [];

    if (my @triggers = __fetch_all_triggers($self, $when)) { # any triggers?
        for my $trigger (@triggers) {
            my @return = $trigger->[0]->($self, @_);
            push @{$result_store->{'_class_trigger_results'}}, \@return;
            return undef if ($trigger->[1] and not $return[0]); # only abort on false values.
    else {
        # if validation is enabled we can only add valid trigger points
        # so we only need to check in call_trigger() if there's no
        # trigger with the requested name.
        __validate_triggerpoint($self, $when);

    return scalar @{$result_store->{'_class_trigger_results'}};

sub __fetch_all_triggers {
    my ($obj, $when, $list, $order, $nocache) = @_;
    $nocache = 0 unless defined $nocache;
    my $class = ref $obj || $obj;
    my $return;
    my $when_key = defined $when ? $when : '';
    unless ($nocache) {
        return __cached_triggers($obj, $when)
            if $Fetch_All_Triggers_Cache{$class}{$when_key};
    unless ($list) {
        # Absence of the $list parameter conditions the creation of
        # the unrolled list of triggers. These keep track of the unique
        # set of triggers being collected for each class and the order
        # in which to return them (based on hierarchy; base class
        # triggers are returned ahead of descendant class triggers).
        $list = {};
        $order = [];
        $return = 1;
    no strict 'refs';
    my @classes = @{$class . '::ISA'};
    push @classes, $class;
    foreach my $c (@classes) {
        next if $list->{$c};
#        if (UNIVERSAL::can($c, 'call_trigger')) {
        if ($c->can('call_trigger')) {
            $list->{$c} = [];
            __fetch_all_triggers($c, $when, $list, $order, 1)
                unless $c eq $class;
            if (defined $when && $Triggers{$c}{$when}) {
                push @$order, $c;
                $list->{$c} = $Triggers{$c}{$when};
    if ($return) {
        my @triggers;
        foreach my $class (@$order) {
            push @triggers, @{ $list->{$class} };

        # Only cache the class triggers, object triggers would
        # necessitate a much larger cache and they're cheap to
        # get anyway.
        $Fetch_All_Triggers_Cache{$class}{$when_key} = \@triggers;

        return __cached_triggers($obj, $when);

sub __cached_triggers {
    my($proto, $when) = @_;
    my $class = ref $proto || $proto;
    return @{ $Fetch_All_Triggers_Cache{$class}{$when || ''} },
           @{ __object_triggers($proto, $when) };

sub __object_triggers {
    my($obj, $when) = @_;
    return [] unless ref $obj && defined $when;
    return $obj->{__triggers}{$when} || [];

sub __validate_triggerpoint {
    return unless my $points = $TriggerPoints{ref $_[0] || $_[0]};
    my ($self, $when) = @_;
    Carp::croak("$when is not valid triggerpoint for ".(ref($self) ? ref($self) : $self))
        unless $points->{$when};

sub __fetch_triggers {
    my ($obj, $proto) = @_;
    # check object based triggers first
    return ref $obj ? $obj->{__triggers} ||= {} : $Triggers{$obj} ||= {};


=head1 NAME

Class::Trigger - Mixin to add / call inheritable triggers


  package Foo;
  use Class::Trigger;

  sub foo {
      my $self = shift;
      # some code ...
      # some code ...

  package main;
  Foo->add_trigger(before_foo => \&sub1);
  Foo->add_trigger(after_foo => \&sub2);

  my $foo = Foo->new;
  $foo->foo;            # then sub1, sub2 called

  # triggers are inheritable
  package Bar;
  use base qw(Foo);

  Bar->add_trigger(before_foo => \&sub);

  # triggers can be object based
  $foo->add_trigger(after_foo => \&sub3);
  $foo->foo;            # sub3 would appply only to this object


Class::Trigger is a mixin class to add / call triggers (or hooks)
that get called at some points you specify.

=head1 METHODS

By using this module, your class is capable of following methods.

=over 4

=item add_trigger

  Foo->add_trigger($triggerpoint => $sub);
  $foo->add_trigger($triggerpoint => $sub);

  Foo->add_trigger( name => $triggerpoint,
                    callback => sub {return undef},
                    abortable => 1); 

  # no further triggers will be called. Undef will be returned.

Adds triggers for trigger point. You can have any number of triggers
for each point. Each coderef will be passed a reference to the calling object, 
as well as arguments passed in via L<call_trigger>. Return values will be
captured in I<list context>.

If add_trigger is called with named parameters and the C<abortable>
parameter is passed a true value, a false return value from trigger
code will stop processing of this trigger point and return a C<false>
value to the calling code.

If C<add_trigger> is called without the C<abortable> flag, return
values will be captured by call_trigger, but failures will be ignored.

If C<add_trigger> is called as object method, whole current trigger
table will be copied onto the object and the new trigger added to
that. (The object must be implemented as hash.)

  my $foo = Foo->new;

  # this trigger ($sub_foo) would apply only to $foo object
  $foo->add_trigger($triggerpoint => $sub_foo);

  # And not to another $bar object
  my $bar = Foo->new;

=item call_trigger

  $foo->call_trigger($triggerpoint, @args);

Calls triggers for trigger point, which were added via C<add_trigger>
method. Each triggers will be passed a copy of the object as the first argument.
Remaining arguments passed to C<call_trigger> will be passed on to each trigger.
Triggers are invoked in the same order they were defined.

If there are no C<abortable> triggers or no C<abortable> trigger point returns 
a false value, C<call_trigger> will return the number of triggers processed.

If an C<abortable> trigger returns a false value, call trigger will stop execution
of the trigger point and return undef.

=item last_trigger_results

    my @results = @{ $foo->last_trigger_results };

Returns a reference to an array of the return values of all triggers called
for the last trigger point. Results are ordered in the same order the triggers
were run.



By default you can make any number of trigger points, but if you want
to declare names of trigger points explicitly, you can do it via

  package Foo;
  use Class::Trigger qw(foo bar baz);

  package main;
  Foo->add_trigger(foo  => \&sub1); # okay
  Foo->add_trigger(hoge => \&sub2); # exception

=head1 FAQ

B<Acknowledgement:> Thanks to everyone at POOP mailing-list

=over 4

=item Q.

This module lets me add subs to be run before/after a specific
subroutine is run.  Yes?

=item A.

You put various call_trigger() method in your class.  Then your class
users can call add_trigger() method to add subs to be run in points
just you specify (exactly where you put call_trigger()).

=item Q.

Are you aware of the perl-aspects project and the Aspect module?  Very
similar to Class::Trigger by the look of it, but its not nearly as
explicit.  Its not necessary for foo() to actually say "triggers go
*here*", you just add them.

=item A.

Yep ;)

But the difference with Aspect would be that Class::Trigger is so
simple that it's easy to learn, and doesn't require 5.6 or over.

=item Q.

How does this compare to Sub::Versive, or Hook::LexWrap?

=item A.

Very similar. But the difference with Class::Trigger would be the
explicitness of trigger points.

In addition, you can put hooks in any point, rather than pre or post
of a method.

=item Q.

It looks interesting, but I just can't think of a practical example of
its use...

=item A.

(by Tony Bowden)

I originally added code like this to Class::DBI to cope with one
particular case: auto-upkeep of full-text search indices.

So I added functionality in Class::DBI to be able to trigger an
arbitary subroutine every time something happened - then it was a
simple matter of setting up triggers on INSERT and UPDATE to reindex
that row, and on DELETE to remove that index row.

See L<Class::DBI::mysql::FullTextSearch> and its source code to see it
in action.


=head1 AUTHORS

Original idea by Tony Bowden E<lt>tony@kasei.comE<gt> in Class::DBI.

Code by Tatsuhiko Miyagawa E<lt>miyagawa@bulknews.netE<gt>.

Jesse Vincent added a code to get return values from triggers and
abortable flag.

=head1 LICENSE

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.

=head1 SEE ALSO