#!/usr/bin/perl
## no critic pod
use strict;
use warnings;

=head1 NAME

cksum-tgz - Checksum the contents of a tarball

=head1 SYNOPSIS

  cksum-tgz tarball.tgz > tarball.cksum

  Options:
    --help
    --man

=head1 DESCRIPTION

This is kind of equivalent to unpacking a tarball, running cksum on
everything in it, then deleting the stuff that was unpacked. It
attempts to keep a minimum of files around on the disk while
operating.

=head1 OPTIONS

=over

=item C<--help>

Shows a short help message.

=item C<--man>

Even more help.

=back

=cut

use Getopt::Long 'GetOptions';
use autouse 'Carp'       => 'croak';
use autouse 'Pod::Usage' => 'pod2usage';

GetOptions(
    man  => sub { pod2usage( -verbose => 2 ) },
    help => sub { pod2usage( -verbose => 1 ) },
    )
    or pod2usage( -verbose => 0 );
@ARGV == 1 or pod2usage( -verbose => 0 );
my ($tgz) = shift @ARGV;

## no critic noisy
open my $tgz_fh, '-|', 'tar', 'xvzf', $tgz
    or croak "Can't tar xvzf $tgz: $!";

# tar will print a file before it is done so I have this reader to
# wait for the next file to get mentioned.
my $file_reader = do {
    my @files;
    sub {

        # Add to @files if necessary and possible.
        while ( @files < 2 and $tgz_fh ) {
            chomp( my $file = <$tgz_fh> );
            if ( not defined $file ) {
                close $tgz_fh;
                undef $tgz_fh;
            }
            else {
                push @files, $file;
            }
        }

        if (@files) {
            return shift @files;
        }
        else {
            return;
        }
    };
};

# For each file, cksum it.
# For each directory, plan to remove it in LIFO order.
my @directories;
while ( my $file = $file_reader->() ) {
    if ( -f $file ) {
        0 == system 'cksum', $file
            or croak "Can't exec cksum $file: $?";
        unlink $file
            or croak "Can't unlink $file: $!";
    }
    elsif ( -d _ ) {
        unshift @directories, $file;
    }
}

# Remove my directories in LIFO order.
while (@directories) {
    my $size_before = @directories;
    @directories = grep { not rmdir } @directories;
    last if @directories == $size_before;
}