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use experimental qw( signatures declared_refs refaliasing );

our $VERSION = '0.33';

use Iterator::Flex::Utils qw( RETURN STATE EXHAUSTION :IterAttrs :IterStates );
use Iterator::Flex::Factory 'to_iterator';
use parent 'Iterator::Flex::Base';
use List::Util 'all';

use namespace::clean;

















































sub new ( $class, @args ) {
    my $pars = Ref::Util::is_hashref( $args[-1] ) ? pop @args : {};

    $class->SUPER::new( {
            depends                => \@args,
            current_iterator_index => undef,
        },
        $pars,
    );
}

sub construct ( $class, $state ) {
    throw_failure( parameter => q{state must be a HASH reference} )
      unless Ref::Util::is_hashref( $state );

    $state->{value} //= [];

    my ( \@depends, $prev, $current, undef, undef )
      = @{$state}{ 'depends', 'prev', 'current', 'next', 'thaw' };

    # transform into iterators if required.
    my @stack
      = map { to_iterator( $_, { ( +EXHAUSTION ) => RETURN } ) } @depends;
    my @snapshot = @stack;

    # --- cargo cult??
    # my $value;
    # $value = $current
    #   if $thaw;

    my $self;

    my $iter;
    my $is_exhausted;
    my $iterator_state;

    my sub init {
        $iterator_state = IterState_EXHAUSTED;
        if ( @stack ) {
            $iter           = $stack[0];
            $is_exhausted   = $iter->can( 'is_exhausted' );
            $iterator_state = IterState_CLEAR;
        }
    }
    init();

    my %params = (

        ( +_NAME ) => 'istack',

        ( +_SELF ) => \$self,

        ( +RESET ) => sub {
            $prev  = $current = undef;
            @stack = @snapshot;
            init();
        },

        ( +REWIND ) => sub {
            @stack = @snapshot;
            init();
        },

        ( +STATE ) => \$iterator_state,

        ( +NEXT ) => sub {
            return $self->signal_exhaustion if $iterator_state == IterState_EXHAUSTED;

            while ( 1 ) {
                my $value = $iter->();

                if ( defined( $value ) || !$iter->$is_exhausted ) {
                    $prev = $current;
                    return $current = $value;