Array::Tour::Serpentine - Return coordinates to take a serpentine path.

  use Array::Tour::Serpentine qw(:directions);

  my $tour = Array::Tour::Serpentine->new(
      dimensions => [5, 5],
      vertical => $vertical,
      corner_right => $corner_right,
      corner_bottom => $corner_bottom);

  $dir = $tour->direction()

  Return the direction we just walked.

  Overrides Array::Tour's direction() method.
=cut

  $ruot = $tour->opposite();

  $self->_set(%parameters);

  Override Array::Tour's _set() method for one that can handle
  our parameters.
=cut

package Array::Tour::Serpentine;

use 5.008;
use strict;
use warnings;
use integer;
use base q(Array::Tour);
use Array::Tour qw(:directions :status);

our $VERSION = '0.06';

sub direction()
{
	my $self = shift;
	return ($self->{status} == STOP)? undef: ${$self->{direction}}[0];
}

sub next
{
	my $self = shift;

	return undef unless ($self->has_next());

	#
	# Set up the conditions for the pacing.
	#
	if ($self->{tourstatus} == START)
	{
		$self->{tourstatus} = TOURING;
		$self->{pacer} = ${$self->{pacing}}[0];
	}
	else
	{
		#
		# Pace off in the current direction.
		#
		my $direction = ${$self->{direction}}[0];
		${$self->{position}}[(($direction & (North | South)) == 0)? 0: 1] +=
			(($direction & (North | West)) == 0)? 1: -1;

		#
		# Will the next pace be in a different direction?
		#
		if (--$self->{pacer} == 0)
		{
			$self->{pacer} = ${$self->{pacing}}[1];
			${$self->{pacing}}[0] += $self->{pacechange};
	
			#
			# Rotate to the next pacing length and the next direction.
			#
			push @{$self->{pacing}}, shift @{$self->{pacing}};
			push @{$self->{direction}}, shift @{$self->{direction}};
		}
	}

	$self->{tourstatus} = STOP if (++$self->{odometer} == $self->{tourlength});
	return $self->adjusted_position();
}

sub opposite()
{
	my $self = shift;
	my %anti_self;
	my @dimensions = @{ $self->{dimensions} };

	$anti_self{dimensions} = $self->{dimensions};

	$anti_self{corner_right} ^=  1;
	$anti_self{corner_bottom} ^= 1;

	return Array::Tour::Serpentine->new(%anti_self);
}

sub _set()
{
	my $self = shift;
	my(%params) = @_;
	my($pace_x, $pace_y) = (1, 1);
	my($start_x, $start_y) = (0, 0);
	my @dirlist = (East, South, West, North);
	my @dimensions = @{$self->{dimensions}};
	my @direction;

	warn "Unknown paramter $_" foreach (grep{$_ !~ /vertical|corner_right|corner_bottom/} (keys %params));

	#
	# Parameter checks.
	#
	# Set corner_right, corner_bottom, and vertical to 0/1 values.
	#
	my $vertical = (defined $params{vertical} and $params{vertical} != 0)? 1: 0;
	my $corner_right = (defined $params{corner_right} and $params{corner_right} != 0)? 1: 0;
	my $corner_bottom = (defined $params{corner_bottom} and $params{corner_bottom} != 0)? 1: 0;

	$pace_x = $dimensions[0] - 1 unless ($vertical);
	$pace_y = $dimensions[1] - 1 if ($vertical);
	$start_x = $dimensions[0] - 1 if ($corner_right);
	$start_y = $dimensions[1] - 1 if ($corner_bottom);

	my $idx0 = ((($corner_bottom & $vertical)|
	            ($corner_right & ($vertical^1))) << 1) | $vertical;
	my $idx1 = ((($corner_bottom & ($vertical^1))|
	            ($corner_right & $vertical)) << 1) | ($vertical ^ 1);
	push @direction, @dirlist[$idx0, $idx1, $idx0 ^ 2, $idx1];

	$self->{corner_right} = $corner_right;
	$self->{corner_bottom} = $corner_bottom;
	$self->{vertical} = $vertical;
	$self->{direction} = \@direction;
	$self->{pacechange} = 0;
	$self->{pacing} = (($direction[0] & (West | East)) == 0)? [$pace_y, $pace_x]: [$pace_x, $pace_y];
	$self->{start} = [$start_x, $start_y];
	$self->{position} = [$start_x, $start_y];

	return $self;
}

1;
__END__