package Test2::API::Stack;
use strict;
use warnings;

our $VERSION = '1.302188';

use Test2::Hub();

use Carp qw/confess/;

sub new {
    my $class = shift;
    return bless [], $class;

sub new_hub {
    my $self = shift;
    my %params = @_;

    my $class = delete $params{class} || 'Test2::Hub';

    my $hub = $class->new(%params);

    if (@$self) {
        $hub->inherit($self->[-1], %params);
    else {
        require Test2::API;
            unless $hub->format || exists($params{formatter});

        my $ipc = Test2::API::test2_ipc();
        if ($ipc && !$hub->ipc && !exists($params{ipc})) {

    push @$self => $hub;


sub top {
    my $self = shift;
    return $self->new_hub unless @$self;
    return $self->[-1];

sub peek {
    my $self = shift;
    return @$self ? $self->[-1] : undef;

sub cull {
    my $self = shift;
    $_->cull for reverse @$self;

sub all {
    my $self = shift;
    return @$self;

sub root {
    my $self = shift;
    return unless @$self;
    return $self->[0];

sub clear {
    my $self = shift;
    @$self = ();

# Do these last without keywords in order to prevent them from getting used
# when we want the real push/pop.

    no warnings 'once';

    *push = sub {
        my $self = shift;
        my ($hub) = @_;
        $hub->inherit($self->[-1]) if @$self;
        push @$self => $hub;

    *pop = sub {
        my $self = shift;
        my ($hub) = @_;
        confess "No hubs on the stack"
            unless @$self;
        confess "You cannot pop the root hub"
            if 1 == @$self;
        confess "Hub stack mismatch, attempted to pop incorrect hub"
            unless $self->[-1] == $hub;
        pop @$self;




=encoding UTF-8

=head1 NAME

Test2::API::Stack - Object to manage a stack of L<Test2::Hub>

=head1 ***INTERNALS NOTE***

B<The internals of this package are subject to change at any time!> The public
methods provided will not change in backwards incompatible ways, but the
underlying implementation details might. B<Do not break encapsulation here!>


This module is used to represent and manage a stack of L<Test2::Hub>
objects. Hubs are usually in a stack so that you can push a new hub into place
that can intercept and handle events differently than the primary hub.


    my $stack = Test2::API::Stack->new;
    my $hub = $stack->top;

=head1 METHODS

=over 4

=item $stack = Test2::API::Stack->new()

This will create a new empty stack instance. All arguments are ignored.

=item $hub = $stack->new_hub()

=item $hub = $stack->new_hub(%params)

=item $hub = $stack->new_hub(%params, class => $class)

This will generate a new hub and push it to the top of the stack. Optionally
you can provide arguments that will be passed into the constructor for the
L<Test2::Hub> object.

If you specify the C<< 'class' => $class >> argument, the new hub will be an
instance of the specified class.

Unless your parameters specify C<'formatter'> or C<'ipc'> arguments, the
formatter and IPC instance will be inherited from the current top hub. You can
set the parameters to C<undef> to avoid having a formatter or IPC instance.

If there is no top hub, and you do not ask to leave IPC and formatter undef,
then a new formatter will be created, and the IPC instance from
L<Test2::API> will be used.

=item $hub = $stack->top()

This will return the top hub from the stack. If there is no top hub yet this
will create it.

=item $hub = $stack->peek()

This will return the top hub from the stack. If there is no top hub yet this
will return undef.

=item $stack->cull

This will call C<< $hub->cull >> on all hubs in the stack.

=item @hubs = $stack->all

This will return all the hubs in the stack as a list.

=item $stack->clear

This will completely remove all hubs from the stack. Normally you do not want
to do this, but there are a few valid reasons for it.

=item $stack->push($hub)

This will push the new hub onto the stack.

=item $stack->pop($hub)

This will pop a hub from the stack, if the hub at the top of the stack does not
match the hub you expect (passed in as an argument) it will throw an exception.


=head1 SOURCE

The source code repository for Test2 can be found at


=over 4

=item Chad Granum E<lt>exodist@cpan.orgE<gt>


=head1 AUTHORS

=over 4

=item Chad Granum E<lt>exodist@cpan.orgE<gt>



Copyright 2020 Chad Granum E<lt>exodist@cpan.orgE<gt>.

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

See F<>