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package CSS::DOM::Rule;

$VERSION = '0.17';

use warnings;
use strict;

use Carp 'croak';
use CSS::DOM::Constants;
use CSS::DOM::Exception qw/ SYNTAX_ERR INVALID_MODIFICATION_ERR /;
use Exporter 5.57 'import';
use Scalar::Util 'weaken';

*EXPORT_OK = $CSS::DOM::Constants::EXPORT_TAGS{rule};
our %EXPORT_TAGS = (all => \our @EXPORT_OK);

use constant 1.03 our $_const = {
# Don’t let these conflict with subclasses!
	prnt => 0,
	shet => 1,
	typs => 2, # token types   These two are not used by subclassed,
	tokn => 3, # tokens        so there’s no chance of a conflict.
};
{ no strict; delete @{__PACKAGE__.'::'}{_const => keys %{our $_const}} }

sub new {
	my $self = bless[],shift;
	my $parent = shift || return $self;
	if($parent->isa('CSS::DOM::Rule')) {
		weaken($$self[shet] = $parent->parentStyleSheet);
		weaken($$self[prnt] = $parent);
	}
	else {
		weaken($$self[shet] = $parent)
	}
	$self;
}

sub type { UNKNOWN_RULE }

# This is used by cssText, both this class’s and subclasses’:
sub _parse { # This method parses the code passed to it and checks to see
             # whether the retval is the same class as  $self,  throwing
             # errors as appropriate.  It returns the new rule resulting
             # from the parse. Each subclass is responsible for extorting
             # the rule data from the new rule.
	my $self = shift;
	require CSS::DOM::Parser;
	my $new_rule  =  CSS::DOM::Parser'parse_statement(shift)
		|| die CSS::DOM::Exception->new(SYNTAX_ERR, $@);

	ref $new_rule eq ref $self or die CSS::DOM::Exception->new(
		INVALID_MODIFICATION_ERR,
		"The rule cannot be converted to a different type."
	);
	$new_rule;
};

sub cssText {
	my $self = shift;
	my $old;
	if(defined wantarray) {
		$old = join '', @{$self->[tokn]},;
		$old .= ';' unless $self->[typs] =~ /[;}]\z/;
		$old .= "\n";
	}
	if (@_) {
		my $new_rule  =  $self->_parse(shift);
		@$self[typs,tokn] = @$new_rule[typs,tokn];
	}
	$old;
};


sub parentStyleSheet { shift->[shet]||() }
sub parentRule       { shift->[prnt]||() }

sub _set_parentStyleSheet { weaken(shift->[shet] = pop) }
sub _set_parentRule       { weaken(shift->[prnt] = pop) }

sub _set_tokens { @{+shift}[typs,tokn] = @_[1,2]; }
  
                              !()__END__()!

=head1 NAME

CSS::DOM::Rule - CSS rule class for CSS::DOM

=head1 VERSION

Version 0.17

=head1 SYNOPSIS

  use CSS::DOM::Rule ':all'; # import constants

  use CSS::DOM;
  $sheet = new CSS::DOM;
  $sheet->insertRule('bla blah blah {}');
  $rule = $sheet->cssRules->[0];
  
  $rule->type; # STYLE_RULE
  $rule->cssText; # 'bla blah blah {}' or similar
  $rule->cssText('p { margin: 0 }'); # replace it
  $rule->parentStyleSheet; # $sheet

=head1 DESCRIPTION

This module provides the CSS rule class for L<CSS::DOM>. It implements
the CSSRule and CSSUnknownRule DOM interfaces.

=head1 METHODS

=head2 Constructor

Only call the constructor on this class to create an 'unknown' rule. You have to
call the constructor on a particular subclass to get another type. Normally
you do not need to 
call this directly anyway. (See L<CSS::DOM>'s 
C<parse> and C<insertRule> methods.) But just in case you do want to call 
it, here it
is:

  new CSS::DOM::Rule $parent; # unknown rule
  
  require CSS::DOM::Rule::Style
  new CSS::DOM::Rule::Style $parent;
  # etc.

C<$parent> is the parent rule, if the rule is nested, or the parent style
sheet otherwise.

=head2 Object Methods

=over 4

=item type

Returns one of the constants below indicating the type of rule.