package FixedSizeQueue;

use Minions
    interface => [qw( push pop size )],

    construct_with  => {
        max_items => {
            assert => { positive_int => sub { $_[0] =~ /^\d+$/ && $_[0] > 0 } },
        },
    },

    implementation => 'FixedSizeQueue::Default',
;

1;

package FixedSizeQueue::Default;

use Minions::Implementation
    has  => {
        q => { default => sub { [ ] } },

        max_size => {
            init_arg => 'max_items',
        },
    },
;

sub size {
    my ($self) = @_;
    scalar @{ $self->{$__q} };
}

sub push {
    my ($self, $val) = @_;

    log_info($self);
    push @{ $self->{$__q} }, $val;

    if ($self->size > $self->{$__max_size}) {
        $self->pop;
    }
}

sub pop {
    my ($self) = @_;

    log_info($self);
    shift @{ $self->{$__q} };
}

sub log_info {
    my ($self) = @_;

    warn sprintf "[%s] I have %d element(s)\n", scalar(localtime), $self->size;
}

1;

##</code><code>##

% reply -I lib
0> use FixedSizeQueue
1> my $q = FixedSizeQueue->new(max_items => 3)
$res[0] = bless( {
         '932db126-' => 'FixedSizeQueue::__Private',
         '932db126-max_size' => 3,
         '932db126-q' => []
       }, 'FixedSizeQueue::__Minions' )

2> $q->can
$res[1] = [
  'pop',
  'push',
  'size'
]

3> $q->push($_) for 1 .. 3
[Mon Jan 26 12:01:53 2015] I have 0 element(s)
[Mon Jan 26 12:01:53 2015] I have 1 element(s)
[Mon Jan 26 12:01:53 2015] I have 2 element(s)
$res[2] = ''

4> $q->pop
[Mon Jan 26 12:02:09 2015] I have 3 element(s)
$res[3] = 1

5> $q
$res[4] = bless( {
         '932db126-' => 'FixedSizeQueue::__Private',
         '932db126-max_size' => 3,
         '932db126-q' => [
                           2,
                           3
                         ]
       }, 'FixedSizeQueue::__Minions' )

6> $q->push($_) for 4 .. 6
[Mon Jan 26 12:02:55 2015] I have 2 element(s)
[Mon Jan 26 12:02:55 2015] I have 3 element(s)
[Mon Jan 26 12:02:55 2015] I have 4 element(s)
[Mon Jan 26 12:02:55 2015] I have 3 element(s)
[Mon Jan 26 12:02:55 2015] I have 4 element(s)
$res[5] = ''

7> $q
$res[6] = bless( {
         '932db126-' => 'FixedSizeQueue::__Private',
         '932db126-max_size' => 3,
         '932db126-q' => [
                           4,
                           5,
                           6
                         ]
       }, 'FixedSizeQueue::__Minions' )

8> $q->log_info()
Can't locate object method "log_info" via package "FixedSizeQueue::__Minions" at reply input line 1.
9>