Event::SlidingWindow - Count events that occur within a fixed sliding window of time

  use Event::SlidingWindow ;

  my $esw = new Event::SlidingWindow(30) ;
  $esw->record_event() ;
  my $cnt = $esw->count_events() ;

package Event::SlidingWindow ;

use strict ;
use Carp ;


$Event::SlidingWindow::VERSION = '0.05' ;


sub new {
	my $class = shift ;
	my $nb_buckets = int(shift) ;		# Number of buckets, i.e. window size
	my $bucket_size = int(shift) || 1 ; # Bucket size in seconds
	
	# Validate paramters...
	if ($nb_buckets <= 0){
		croak("nb_buckets must be an integer > 0") ;
	}
	
	my $this = {
		nb_buckets => $nb_buckets,
		bucket_size => $bucket_size,
		loop => [],
	} ;

	bless($this, $class) ;
	$this->_init() ;
	
	return $this ;
}


sub _init {
	my $this = shift ;
	my $now = shift || time() ;
	
	$this->{cur_ts} = $now ;
	for (my $i = 0 ; $i < $this->{nb_buckets} ; $i++){
		$this->{loop}->[$i] = 0 ;
	}
	$this->{cur_idx} = 0 ;
}


sub record_event {
	my $this = shift ;
	my $now = shift ;
	my $incr = shift || 1 ;
	
	$this->_update($now) ;
	$this->{loop}->[$this->{cur_idx}] += $incr ;
}


sub count_events {
	my $this = shift ;
	my $now = shift ;
	
	$this->_update($now) ;
	my $cnt = 0 ;
	foreach my $c (@{$this->{loop}}){
		$cnt += $c ;
	}
	
	return $cnt ;
}


# This method is responsible for keeping the loop in sync for
# from current time value.
sub _update {
	my $this = shift ;
	my $now = shift || time() ;

	my $interval = int(($now - $this->{cur_ts}) / $this->{bucket_size}) ;
	if (! $interval){
		return ;
	}
	if ($interval >= $this->{nb_buckets}){
		$this->_init($now) ;
		return ;
	}
	
	# Now we really have some work to do.
	for (my $i = 0 ; $i < $interval ; $i++){
		$this->{loop}->[($this->{cur_idx} + $i + 1) % $this->{nb_buckets}] = 0 ;
	}	
	$this->{cur_idx} = ($this->{cur_idx} + $interval) % $this->{nb_buckets} ;
	$this->{cur_ts} = $now ;
}


sub _dump {
	my $this = shift ;
	
	my @ret = () ;
	for (my $i = 0 ; $i < $this->{nb_buckets} ; $i++){
		push @ret, $this->{loop}->[($this->{cur_idx} + $i + 1) % $this->{nb_buckets}] ;
	}
	
	return \@ret ;
}


1 ;


__END__