package Text::Tabs;

require Exporter;

@ISA = (Exporter);
@EXPORT = qw(expand unexpand $tabstop);

use vars qw($VERSION $SUBVERSION $tabstop $debug);
$VERSION = 2012.0818;
$SUBVERSION = 'modern';

use strict;

use 5.010_000;

BEGIN {
$tabstop = 8;
$debug = 0;
}

my $CHUNK = qr/\X/;

sub _xlen (_) { scalar(() = $_[0] =~ /$CHUNK/g) }
sub _xpos (_) { _xlen( substr( $_[0], 0, pos($_[0]) ) ) }

sub expand {
my @l;
my $pad;
for ( @_ ) {
my $s = '';
for (split(/^/m, $_, -1)) {
my $offs = 0;
s{\t}{
# this works on both 5.10 and 5.11
$pad = $tabstop - (_xlen(${^PREMATCH}) + $offs) % $tabstop;
# this works on 5.11, but fails on 5.10
#XXX# $pad = $tabstop - (_xpos() + $offs) % $tabstop;
$offs += $pad - 1;
" " x $pad;
}peg;
$s .= $_;
}
push(@l, $s);
}
return @l if wantarray;
return $l[0];
}

sub unexpand
{
my (@l) = @_;
my @e;
my $x;
my $line;
my @lines;
my $lastbit;
my $ts_as_space = " " x $tabstop;
for $x (@l) {
@lines = split("\n", $x, -1);
for $line (@lines) {
$line = expand($line);
@e = split(/(${CHUNK}{$tabstop})/,$line,-1);
$lastbit = pop(@e);
$lastbit = ''
unless defined $lastbit;
$lastbit = "\t"
if $lastbit eq $ts_as_space;
for $_ (@e) {
if ($debug) {
my $x = $_;
$x =~ s/\t/^I\t/gs;
print "sub on '$x'\n";
}
s/ +$/\t/;
}
$line = join('',@e, $lastbit);
}
$x = join("\n", @lines);
}
return @l if wantarray;
return $l[0];
}

1;
__END__

sub expand
{
my (@l) = @_;
for $_ (@l) {
1 while s/(^|\n)([^\t\n]*)(\t+)/
$1. $2 . (" " x
($tabstop * length($3)
- (length($2) % $tabstop)))
/sex;
}
return @l if wantarray;
return $l[0];
}