#!/usr/bin/env perl
package HTML::RewriteAttributes;
use strict;
use warnings;
use base 'HTML::Parser';
use Carp 'croak';
use HTML::Entities 'encode_entities';

our $VERSION = '0.05';

sub new {
    my $class = shift;
    return $class->SUPER::new(
        start_h   => [ '_start_tag', "self,tagname,attr,attrseq,text" ],
        default_h => [ '_default',   "self,tagname,attr,text"         ],
    );
}

sub rewrite {
    my $self = shift;
    $self = $self->new if !ref($self);
    $self->_rewrite(@_);
}

sub _rewrite {
    my $self = shift;
    my $html = shift;
    my $cb   = shift || sub { $self->rewrite_resource(@_) };

    $self->_begin_rewriting($cb);

    $self->parse($html);
    $self->eof;

    $self->_done_rewriting;

    return $self->{rewrite_html};
}

sub rewrite_resource {
    my $self = shift;
    my $class = ref($self) || $self;

    my $error = "You must specify a callback to $class->rewrite";
    $error .= " or define $class->rewrite_resource" if $class ne __PACKAGE__;
    croak "$error.";
}

sub _begin_rewriting {
    my $self = shift;
    my $cb   = shift;

    $self->{rewrite_html} = '';
    $self->{rewrite_callback} = $cb;
}

sub _done_rewriting { }

sub _should_rewrite { 1 }

sub _start_tag {
    my ($self, $tag, $attrs, $attrseq, $text) = @_;

    $self->{rewrite_html} .= "<$tag";

    for my $attr (@$attrseq) {
        next if $attr eq '/';

        if ($self->_should_rewrite($tag, $attr)) {
            $attrs->{$attr} = $self->_invoke_callback($tag, $attr, $attrs->{$attr});
            next if !defined($attrs->{$attr});
        }

        $self->{rewrite_html} .= sprintf ' %s="%s"',
                                    $attr,
                                    encode_entities($attrs->{$attr});
    }

    $self->{rewrite_html} .= ' /' if $attrs->{'/'};
    $self->{rewrite_html} .= '>';
}

sub _default {
    my ($self, $tag, $attrs, $text) = @_;
    $self->{rewrite_html} .= $text;
}

sub _invoke_callback {
    my $self = shift;
    my ($tag, $attr, $value) = @_;

    return $self->{rewrite_callback}->($tag, $attr, $value);
}

1;

__END__

=head1 NAME

HTML::RewriteAttributes - concise attribute rewriting

=head1 SYNOPSIS

    $html = HTML::RewriteAttributes->rewrite($html, sub {
        my ($tag, $attr, $value) = @_;

        # delete any attribute that mentions..
        return if $value =~ /COBOL/i;

        $value =~ s/\brocks\b/rules/g;
        return $value;
    });


    # writing some HTML email I see..
    $html = HTML::RewriteAttributes::Resources->rewrite($html, sub {
        my $uri = shift;
        my $content = render_template($uri);
        my $cid = generate_cid_from($content);
        $mime->attach($cid => content);
        return "cid:$cid";
    });


    # up for some HTML::ResolveLink?
    $html = HTML::RewriteAttributes::Links->rewrite($html, "http://search.cpan.org");

    # or perhaps HTML::LinkExtor?
    HTML::RewriteAttributes::Links->rewrite($html, sub {
        my ($tag, $attr, $value) = @_;
        push @links, $value;
        $value;
    });

=head1 DESCRIPTION

C<HTML::RewriteAttributes> is designed for simple yet powerful HTML attribute
rewriting.

You simply specify a callback to run for each attribute and we do the rest
for you.

This module is designed to be subclassable to make handling special cases
eaiser. See the source for methods you can override.

=head1 METHODS

=head2 C<new>

You don't need to call C<new> explicitly - it's done in L</rewrite>. It takes
no arguments.

=head2 C<rewrite> HTML, callback -> HTML

This is the main interface of the module. You pass in some HTML and a callback,
the callback is invoked potentially many times, and you get back some similar
HTML.

The callback receives as arguments the tag name, the attribute name, and the
attribute value (though subclasses may override this --
L<HTML::RewriteAttributes::Resources> does). Return C<undef> to remove the
attribute, or any other value to set the value of the attribute.

=head1 SEE ALSO

L<HTML::Parser>, L<HTML::ResolveLink>, L<Email::MIME::CreateHTML>,
L<HTML::LinkExtor>

=head1 THANKS

Some code was inspired by, and tests borrowed from, Miyagawa's
L<HTML::ResolveLink>.

=head1 AUTHOR

Shawn M Moore, C<< <sartak@bestpractical.com> >>

=head1 LICENSE

Copyright 2008-2010 Best Practical Solutions, LLC.
HTML::RewriteAttributes is distributed under the same terms as Perl itself.

=cut