use strict;
use warnings;

package FastRanges;

sub new($$$) {
	my $class      = shift;
	my $max_length = shift;
	my $ranges_a   = shift;
	my @lookup;
	for ( @{$ranges_a} ) {
		my ( $start, $end ) = @$_;
		my @idx
			= $end >= $start
			? $start .. $end
			: ( $start .. $max_length, 1 .. $end );
		for my $i (@idx) { $lookup[$i] .= pack 'L', $end }
	}
	bless \@lookup, $class;
}

sub num_ranges_containing($$$) {
	my $self = shift;
	my ( $start, $end ) = @_;    # query range coordinates

	return 0
		unless ( defined $self->[$start] )
		;    # no ranges overlap the start position of the query

	if ( $end >= $start ) {

		# query range is simple
		# any inverted range in {LOOKUP}[$start] must contain it,
		# and so does any simple range which ends at or after $end
		return 0 + grep { $_ < $start or $end <= $_ } unpack 'L*',
			$self->[$start];
	}
	else {

		# query range is inverted
		# only inverted ranges in {LOOKUP}[$start] which also end
		# at of after $end contain it. simple ranges can't contain
		# the query range
		return 0 + grep { $_ < $start and $end <= $_ } unpack 'L*',
			$self->[$start];
	}
}

1;