use strict;
use warnings;

my $buffer = new ();

print "Buffer has ", $buffer->count (), " values\n";
$buffer->push ($_) for 1 .. 200;
print "Buffer has ", $buffer->count (), " values\n";
$buffer->pop () for 1 .. 100;
print "Buffer has ", $buffer->count (), " values\n";
$buffer->push ($_ + 200) for 1 .. 150;
print "Buffer has ", $buffer->count (), " values\n";


sub new {
    my @bufferArray;
    my $buffSize = 256;
    
    $#bufferArray = 256; # set buffer size
    return $buffer = bless {
        buffer => \@bufferArray,
        in => 0,
        out => 0,
        buffSize => $buffSize,
        };
}


sub count {
    my ($self) = @_;
    my $used = $self->{in} - $self->{out};
    
    $used += $self->{buffSize} if $used < 0;
    return $used;
}


sub pop {
    my ($self) = @_;
    
    die "Buffer underflow" if $self->{in} == $self->{out};
    
    my $value = $self->{buffer}[$self->{out}];
    $self->{out} = ($self->{out} + 1) % $self->{buffSize};
    return $value;
}


sub push {
    my ($self, $value) = @_;
    
    die "Buffer overflow" if $self->count () + 1 == $self->{buffSize};
    $self->{buffer}[$self->{in}] = $value;
    $self->{in} = ($self->{in} + 1) % $self->{buffSize};
}