use warnings; use strict;

use Getopt::Long
  qw( :config  gnu_compat no_ignore_case
      no_debug
    ) ;

my %opt =
 ( 'clobber' => 0
 , 'backup-suffix' => '--OLD'
 , 'text' => 'lc $_[0]'
 , 'url'  => undef
 ) ;
my @files = handle_options();

#  Compile code strings.
foreach my $c qw(text url)
{
  next unless $opt{$c};
  $opt{$c} = eval "sub { $opt{$c} }";
}

#  Use the File::Temp in non-OO mode to get both the filename & the
#  filehandle; OO mode can return only the filename.
use File::Temp qw( tempfile );
use File::Copy;
use HTML::TreeBuilder;

foreach my $f ( @files )
{
  my $message = sanity_check($f);
  if ( $message ) { warn $message; next; }

  my $tree = make_html_tree($f);
  #  Make changes.
  foreach my $node ( $tree->look_down('_tag' , 'a') )
  {
    #  Change link text.
    if ( ref $opt{'text'} && scalar $node->content_refs_list)
    {
      foreach my $text ( $node->content_refs_list  )
      {
        next if ref $$text;
        $$text = $opt{'text'}->($$text);
      }
    }

    #  Change link URL.
    my $url = $node->attr('href');
    $node->attr( 'href' , $opt{'url'}->($url) )
      if ref $opt{'url'} && $url ;
  }

  #  Save changes.
  my ($fh , $new_name) = open_new_file($f);
  print $fh $tree->as_HTML;
  $tree = $tree->delete;

  close $fh or die "Could not close $new_name\n";
}

exit;

#  Given a file name, returns the  HTML::TreeBuilder object.
sub make_html_tree
{
  my ($file) = @_;
  my $tree = HTML::TreeBuilder->new;
  $tree->warn(1);
  #  Configure parsing.
  $tree->no_space_compacting(1);
  $tree->ignore_ignorable_whitespace(0);
  $tree->ignore_unknown(0);
  $tree->store_comments(1);
  $tree->store_declarations(1);
  $tree->store_pis(1);
  #
  $tree->parse_file($file);
  $tree->eof;
  $tree->elementify;
  return $tree;
}

#  Given a file name, checks if it is plain readable file and if clobbering
#  specified if it is writable too.  Returns undef if sanity is ok.
sub sanity_check
{
  my ($f) = @_;
  stat $f;
  return
    !( -f _ && -r _ )
    ? "'$f' skipped, either it is not a plain file or is unreadable\n"
    : $opt{'clobber'} && ! -w _
      ? "'$f' skipped, clobbering specified but file is not writable\n"
      : undef;
}

#  Returns file handle (to a new file) and optionally a file name.
sub open_new_file
{
  my ($old) = @_;
  my @open = $opt{'clobber'} ? tempfile() : backup_and_open($old);

  #  Return file handle in scalar context.
  return wantarray ? @open : $open[0];
}

#  Copies the given file to backup; opens the copy and returns the file handle
#  and the given file name (to be consistent w/ File::Temp::tempfile()).
{
  my $FH;
  sub backup_and_open
  {
    my ($old) = @_;
    my $backup = $old . $opt{'backup-suffix'};
    copy $old , $backup or die "Could not make backup: $!";

    open $FH, '>'  , $old or die "Could not open '$old' to write: $!";
    return ($FH , $old);
  }
}

#  Handle options.
sub handle_options
{
  GetOptions
  ( 'help|usage' => \$opt{'usage'}
  , 'no-clobber' => \$opt{'clobber'}
  , 'clobber'    => \$opt{'clobber'}
  , 'i|suffix'   => \$opt{'backup-suffix'}
  , 'text=s'     => \$opt{'text'}
  , 'url=s'      => \$opt{'url'}
  )
    or die 'Wrong option(s) given' , options_doc();
  if ( $opt{'usage'} )
  {
    print "$0 [options] file [file file ...]\n" , options_doc();
    exit 0;
  }
  die "Give at least one HTML file to work with.\n"
    unless scalar @ARGV;

  #  Files to work on.
  return @ARGV;
}

#  Document the options.
sub options_doc
{
  return <<_USAGE_;
 Options are ...

    -help       Show this message.

  File Output:

    -no-clobber Save the original files as a backups. (Default)
    -clobber    Overwrite the given files.  This overrides the
                -no-clobber option.
    -suffix     Text to append at the end of backup. (Default is
                '--OLD'.)

  Code (given as a string which is run inside a sub{}; last value
  returned from the sub is used as then new value for text or URL):

    -text       Code to run over text of each link.  (Default is to
                lowercase the text.)
    -url        Code to run over url of each link.  (Default is
                nothing to do.)
_USAGE_
}