package HTML::TreeBuilder::XPath;

use strict;
use warnings;

use vars qw($VERSION);

$VERSION = '0.08';

package HTML::TreeBuilder::XPath;

use base( 'HTML::TreeBuilder');


package HTML::TreeBuilder::XPath::Node;

sub isElementNode   { 0 }
sub isAttributeNode { 0 }
sub isNamespaceNode { 0 }
sub isTextNode      { 0 }
sub isProcessingInstructionNode { 0 }
sub isPINode        { 0 }
sub isCommentNode   { 0 }

sub getChildNodes { return wantarray ? () : []; }
sub getFirstChild { return undef; }
sub getLastChild { return undef; }


sub to_number { return XML::XPathEngine::Number->new( shift->getValue); }

sub cmp
  { my( $a, $b)=@_;

    # comparison with the root (in $b, or processed in HTML::TreeBuilder::XPath::Root)
    if( $b->isa( 'HTML::TreeBuilder::XPath::Root') ) { return -1; }

    # easy cases
    return  0 if( $a == $b);    
    return 1 if( $a->is_inside($b)); # a starts after b 
    return -1 if( $b->is_inside($a)); # a starts before b

    # lineage does not include the element itself
    my @a_pile= ($a, $a->lineage); 
    my @b_pile= ($b, $b->lineage);
    
    # the 2 elements are not in the same twig
    unless( $a_pile[-1] == $b_pile[-1]) 
      { warn "2 nodes not in the same pile: ", ref( $a), " - ", ref( $b), "\n"; 
        print "a: ", $a->string_value, "\nb: ", $b->string_value, "\n";
      }
    return undef unless( $a_pile[-1] == $b_pile[-1]);

    # find the first non common ancestors (they are siblings)
    my $a_anc= pop @a_pile;
    my $b_anc= pop @b_pile;

    while( $a_anc == $b_anc) 
      { $a_anc= pop @a_pile;
        $b_anc= pop @b_pile;
      }

    if( defined( $a_anc->{_rank}) && defined( $b_anc->{_rank}))
      { return $a_anc->{_rank} <=> $b_anc->{_rank}; }
    else
      { warn "no rank found";
        # from there move left and right and figure out the order
        my( $a_prev, $a_next, $b_prev, $b_next)= ($a_anc, $a_anc, $b_anc, $b_anc);
        while()
          { $a_prev= $a_prev->getPreviousSibling || return -1;
            return  1 if( $a_prev == $b_anc);
            $a_next= $a_next->getNextSibling     || return  1;
            return -1 if( $a_next == $b_anc);
            $b_prev= $b_prev->getPreviousSibling || return  1;
            return -1 if( $b_prev == $a_next);
            $b_next= $b_next->getNextSibling     || return -1;
            return  1 if( $b_next == $a_prev);
          }
      }
  }


# need to modify directly the HTML::Element package, because HTML::TreeBuilder won't let me
# change the class of the nodes it generates
package HTML::Element;
use Scalar::Util qw(weaken);
use vars qw(@ISA);

push @ISA, 'HTML::TreeBuilder::XPath::Node';

use XML::XPathEngine;

{ my $xp;
  sub xp
    { $xp ||=XML::XPathEngine->new();
      return $xp;
    }
}

sub findnodes           { my( $elt, $path)= @_; return xp->findnodes(           $path, $elt); }
sub findnodes_as_string { my( $elt, $path)= @_; return xp->findnodes_as_string( $path, $elt); }
sub findvalue           { my( $elt, $path)= @_; return xp->findvalue(           $path, $elt); }
sub exists              { my( $elt, $path)= @_; return xp->exists(              $path, $elt); }
sub find_xpath          { my( $elt, $path)= @_; return xp->find(                $path, $elt); }
sub matches             { my( $elt, $path)= @_; return xp->matches( $elt, $path, $elt); }
sub set_namespace       { my $elt= shift; xp->new->set_namespace( @_); }

sub getRootNode
  { my $elt= shift;
    # The parent of root is a HTML::TreeBuilder::XPath::Root
    # that helps getting the tree to mimic a DOM tree
    return $elt->root->getParentNode; # I like this one!
  }

sub getParentNode
  { my $elt= shift;
    return $elt->{_parent} || bless { _root => $elt }, 'HTML::TreeBuilder::XPath::Root';
  }
sub getName             { return shift->tag;   }
sub getNextSibling      { my( $elt)= @_; 
                          my $parent= $elt->{_parent} || return undef;
                          return  $parent->_child_as_object( scalar $elt->right, ($elt->{_rank} || 0) + 1);
                        }
sub getPreviousSibling  { my( $elt)= @_; 
                          my $parent= $elt->{_parent} || return undef;
                          return undef unless $elt->{_rank};
                          return  $parent->_child_as_object( scalar $elt->left, $elt->{_rank} - 1); 
                        }
sub isElementNode       { return ref $_[0] && ($_[0]->{_tag}!~ m{^~}) ? 1 : 0; }
sub isCommentNode       { return ref $_[0] && ($_[0]->{_tag} eq '~comment') ? 1 : 0; }
sub isProcessingInstructionNode { return ref $_[0] && ($_[0]->{_tag} eq '~pi') ? 1 : 0; }
sub isTextNode          { return ref $_[0] ? 0 : 1; }

sub getValue 
  { my $elt= shift;
    if( $elt->isCommentNode) { return $elt->{_text}; }
    return $elt->as_text;
  }
        
sub getChildNodes    
  { my $parent= shift;
    my $rank=0;
    my @children= map { $parent->_child_as_object( $_, $rank++) } $parent->content_list;
    return wantarray ? @children : \@children;
  }

sub getFirstChild
  { my $parent= shift;
    my @content= $parent->content_list;
    if( @content)
      { return $parent->_child_as_object( $content[0], 0); }
    else
      { return undef; }
  }
sub getLastChild
  { my $parent= shift;
    my @content= $parent->content_list;
    if( @content)
      { return $parent->_child_as_object( $content[-1], $#content); }
    else
      { return undef; }
  }

sub getAttributes
  { my $elt= shift;
    my %atts= $elt->all_external_attr;
    my $rank=0;
    my @atts= map { bless( { _name => $_, _value => $atts{$_}, 
                             _elt => $elt, _rank => $rank++, 
                           }, 
                               'HTML::TreeBuilder::XPath::Attribute'
                         )
                  } sort keys %atts;
    return wantarray ? @atts : \@atts;
  }

sub to_number { return XML::XPathEngine::Number->new( $_[0]->as_text); }
sub string_value 
  { my $elt= shift;
    if( $elt->isCommentNode) { return $elt->{_text}; }
    return $elt->as_text;
  };

# called on a parent, with a child as second argument and its rank as third
# returns the child if it is already an element, or
# a new HTML::TreeBuilder::XPath::Text element if it is a plain string
sub _child_as_object
  { my( $elt, $elt_or_text, $rank)= @_;
    return undef unless( defined $elt_or_text);
    if( ! ref $elt_or_text)
      { # $elt_or_text is a string, turn it into a TextNode object
        $elt_or_text= bless { _content => $elt_or_text, _parent => $elt, }, 
                            'HTML::TreeBuilder::XPath::TextNode'
                      ;
      }
    if( ref $rank) { warn "rank is a ", ref( $rank), " elt_or_text is a ", ref( $elt_or_text); } 
    $elt_or_text->{_rank}= $rank; # used for sorting;
    return $elt_or_text;
  }

package HTML::TreeBuilder::XPath::TextNode;

use base 'HTML::TreeBuilder::XPath::Node';

sub getParentNode { return shift->{_parent};    }
sub getValue      { return shift->{_content};   }
sub isTextNode    { return 1;                   }
sub getAttributes { return wantarray ? () : []; }
sub as_XML        { return shift->getValue;     }


sub getPreviousSibling
  { my $self= shift;
    my $rank= $self->{_rank}; 
    #unless( defined $self->{_rank})
    #  { warn "no rank for text node $self->{_content}, parent is $self->{_parent}->{_tag}\n"; }
    my $parent= $self->{_parent};
    return $rank ? $parent->_child_as_object( $parent->{_content}->[$rank-1], $rank-1) : undef;
  }

sub getNextSibling
  { my $self= shift;
    my $rank= $self->{_rank};
    #unless( defined $self->{_rank})
    #  { warn "no rank for text node $self->{_content}, parent is $self->{_parent}->{_tag}\n"; }
    my $parent= $self->{_parent};
    my $next_sibling= $parent->{_content}->[$rank+1];
    return defined( $next_sibling) ? $parent->_child_as_object( $next_sibling, $rank+1) : undef;
  }

sub getRootNode
  { return shift->{_parent}->getRootNode; }

sub string_value { return shift->{_content}; }

# added to provide element-like methods to text nodes, for use by cmp
sub lineage 
  { my( $node)= @_;
    my $parent= $node->{_parent};
    return( $parent, $parent->lineage);
  }

sub is_inside
  { my( $text, $node)= @_;
    return $text->{_parent}->is_inside( $node);
  }

1;


package HTML::TreeBuilder::XPath::Attribute;
use base 'HTML::TreeBuilder::XPath::Node';

sub getParentNode   { return $_[0]->{_elt}; }
sub getValue        { return $_[0]->{_value}; }
sub getName         { return $_[0]->{_name} ; }
sub getLocalName    { (my $name= $_[0]->{_name}) =~ s{^.*:}{}; $name; }
sub string_value    { return $_[0]->{_value}; }
sub to_number       { return XML::XPathEngine::Number->new( $_[0]->{_value}); }
sub isAttributeNode { 1 }
sub toString        { return qq{$_[0]->{_name}="$_[0]->{_value}"}; }

# awfully inefficient, but hopefully this is called only for weird (read test-case) queries
sub getPreviousSibling
  { my $self= shift;
    my $rank= $self->{_rank};
    return undef unless $rank;
    my %atts= $self->{_elt}->all_external_attr;
    my $previous_att_name= (sort keys %atts)[$rank-1]; 
    return bless( { _name => $previous_att_name, 
                             _value => $atts{$previous_att_name}, 
                             _elt => $self->{_elt}, _rank => $rank-1, 
                   }, 'HTML::TreeBuilder::XPath::Attribute'
                );
  }

sub getNextSibling
  { my $self= shift;
    my $rank= $self->{_rank};
    my %atts= $self->{_elt}->all_external_attr;
    my $next_att_name= (sort keys %atts)[$rank+1] || return undef; 
    return bless( { _name => $next_att_name, _value => $atts{$next_att_name}, 
                             _elt => $self->{_elt}, _rank => $rank+1, 
                   }, 'HTML::TreeBuilder::XPath::Attribute'
                );
    
  }



# added to provide element-like methods to attributes, for use by cmp
sub lineage 
  { my( $att)= @_;
    my $elt= $att->{_elt};
    return( $elt, $elt->lineage);
  }

sub is_inside
  { my( $att, $node)= @_;
    return ($att->{_elt} == $node) || $att->{_elt}->is_inside( $node);
  }

1;


package HTML::TreeBuilder::XPath::Root;

use base 'HTML::TreeBuilder::XPath::Node';
    
sub getParentNode   { return (); }
sub getChildNodes   { my @content= ( $_[0]->{_root}); return wantarray ? @content : \@content; }
sub getAttributes   { return []        }
sub isDocumentNode  { return 1         }

# added to provide element-like methods to root, for use by cmp
sub lineage {  return ($_[0]); }
sub is_inside { return 0; }
sub cmp { return $_[1]->isa( ' HTML::TreeBuilder::XPath::Root') ? 0 : 1; }

1;

__END__
=head1 NAME

HTML::TreeBuilder::XPath - add XPath support to HTML::TreeBuilder

=head1 SYNOPSIS

  use HTML::TreeBuilder::XPath;
  my $tree= HTML::TreeBuilder::XPath->new;
  $tree->parse_file( "mypage.html");
  my $nb=$tree->findvalue( '/html/body//p[@class="section_title"]/span[@class="nb"]');
  my $id=$tree->findvalue( '/html/body//p[@class="section_title"]/@id');

  my $p= $html->findnodes( '//p[@id="toto"]')->[0];
  my $link_texts= $p->findvalue( './a'); # the texts of all a elements in $p
  
  
=head1 DESCRIPTION

This module adds typical XPath methods to HTML::TreeBuilder, to make it
easy to query a document.

=head1 METHODS

Extra methods added both to the tree object and to each element:

=head2 findnodes ($path)

Returns a list of nodes found by C<$path>.
In scalar context returns an C<Tree::XPathEngine::NodeSet> object.

=head2 findnodes_as_string ($path)

Returns the text values of the nodes

=head2 findvalue ($path)

Returns either a C<Tree::XPathEngine::Literal>, a C<Tree::XPathEngine::Boolean>
or a C<Tree::XPathEngine::Number> object. If the path returns a NodeSet,
$nodeset->xpath_to_literal is called automatically for you (and thus a
C<Tree::XPathEngine::Literal> is returned). Note that
for each of the objects stringification is overloaded, so you can just
print the value found, or manipulate it in the ways you would a normal
perl value (e.g. using regular expressions).

=head2 exists ($path)

Returns true if the given path exists.

=head2 matches($path)

Returns true if the element matches the path.

=head2 find ($path)

The find function takes an XPath expression (a string) and returns either a
Tree::XPathEngine::NodeSet object containing the nodes it found (or empty if
no nodes matched the path), or one of XML::XPathEngine::Literal (a string),
XML::XPathEngine::Number, or XML::XPathEngine::Boolean. It should always
return something - and you can use ->isa() to find out what it returned. If
you need to check how many nodes it found you should check $nodeset->size.
See L<XML::XPathEngine::NodeSet>.



=head1 SEE ALSO

L<HTML::TreeBuilder>

L<XML::XPathEngine>

=head1 AUTHOR

Michel Rodriguez, E<lt>imirod@cpan.orgE<gt>

=head1 COPYRIGHT AND LICENSE

Copyright (C) 2006 by Michel Rodriguez

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself, either Perl version 5.8.4 or,
at your option, any later version of Perl 5 you may have available.


=cut
