#!/usr/bin/perl -w

# apt-show-versions - Lists available package versions with distribution

# This program parses the dpkg status file and the APT lists for the
# installed and available package versions and distribution and shows
# upgrade options within the specific distribution of the selected
# package

# Copyright (C) 2001 - 2014 Christoph Martin

# Author: Christoph Martin <martin@uni-mainz.de>
# Maintainer: Christoph Martin <martin@uni-mainz.de>
my $VERSION ='0.22.15'; # Used by ExtUtils::MakeMaker:

# This file is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 2, or (at your option) any
# later version.

# This file is distributed in the hope that it will be
# useful, but WITHOUT ANY WARRANTY; without even the implied warranty
# of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this file; see the file 'copyright' respectively
# '/usr/share/common-licenses/GPL-2'.  If not, write to the
# Free Software Foundation, Inc.,
# 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA

use strict;
use Getopt::Long;
use Storable qw(nstore retrieve);

my $apackagescachefile="/var/cache/apt-show-versions/apackages-multiarch";
my $ipackagescachefile="/var/cache/apt-show-versions/ipackages-multiarch";
my $filescachefile="/var/cache/apt-show-versions/files";
my $cachefilemode=0644;

use AptPkg::Cache;
use AptPkg::Config '$_config';
use AptPkg::Policy;
use AptPkg::System '$_system';
use AptPkg::Version;

Getopt::Long::Configure('no_ignore_case');  # Distinguish options -R and -r.

$_config->init;
$_config->{quiet} = 2;  # Suppress cache building messages.
$_system = $_config->system;
my $vs = $_system->versioning;
my $cache = AptPkg::Cache->new;
my $policy = $cache->policy;

# Provide some constants (to avoid redundant literals).
my $ARCHIVE  = 'Archive';
my $CODENAME = 'Codename';
my $NAME     = 'Name';
my $PACKAGE  = 'Package';
my $RELEASE  = 'Release';
my $STATUS   = 'Status';
my $SUITE    = 'Suite';
my $UNKNOWN  = 'unknown';
my $VERS     = 'Version';
my $ARCH     = 'Architecture';

# process commandline parameters
my %opts;
# If more than one packages are requested by name, each one gets registered
# in hash %pkg_names as a key (with a true value).
my %pkg_names = ();
unless (GetOptions (\%opts,
        'status-file|stf=s',
        'list-dir|ld=s',
        'package|p=s',
        'regex|r',
        'regex-all|R',
        'allversions|a',
        'upgradeable|u',
        'brief|b',
        'nohold|nh',
        'initialize|i',
        'verbose|v',
	'version|V',
        'help|h')) {
    exit 1;
}
if (scalar @ARGV == 1) {
    if (exists $opts{'package'}) {
        &die(1, "apt-show-versions: too many arguments\n");
    }
    $opts{'package'} = $ARGV[0];
} elsif (scalar @ARGV > 1) {
    if (exists($opts{'package'}) or exists($opts{'regex'})) {
        &die(1, "apt-show-versions: too many arguments\n");
    }
    $pkg_names{$_} = 1 foreach (@ARGV);
}

# Consider implicit option dependencies.
$opts{'regex'} = 1 if ($opts{'regex-all'});

# Determine call mode.
my $MODE_SINGLE   = 1;  # Called with one package name.
my $MODE_MULTIPLE = 2;  # Called with several packages names.
my $MODE_REGEX    = 3;  # Called with a package name regular expression.
my $MODE_ALL      = 4;  # Called without any package information: all packages.
my $mode;
if (%pkg_names) {
    $mode = $MODE_MULTIPLE;
}
elsif ($opts{'regex'}) {
    $mode = $MODE_REGEX;
}
elsif ($opts{'package'}) {
    $mode = $MODE_SINGLE;
}
else {
    $mode = $MODE_ALL;
}

if ($opts{'version'}) {
    print "Apt-Show-Versions $VERSION (c) Christoph Martin\n";
    exit;
}

if (exists $opts{'help'}) {
    print <<EOF;
Apt-Show-Versions $VERSION (c) Christoph Martin

Usage:
 apt-show-versions         shows available versions of installed packages.

Options:
 -stf|--status-file=<file>  Use <file> as the dpkg status file instead
                            of /var/lib/dpkg/status
 -ld|list-dir=<directory>   Use <directory> as path to apt's list files instead
                            of /var/state/apt/lists/ or /var/lib/apt/lists/
 -p|--package=<package>     Print versions for <package>.
 -r|--regex                 Read package with -p as regex
 -R|--regex-all             Like --regex, but also show not installed packages.
 -u|--upgradeable           Print only upgradeable packages
 -a|--allversions           Print all available versions.
 -b|--brief                 Short output.
 -nh|--nohold               Don't treat holded packages.
 -i|--initialize            Initialize or update package cache only (as root).
 -v|--verbose               Verbose messages.
 -V|--version		    Prints apt-show-versions version
 -h|--help                  Print this help.
EOF
    exit;
}

# Path to apt's list files
my $list_dir;
if ($opts{'list-dir'}) {
    $list_dir = $opts{'list-dir'};
}
else {
    $list_dir = $_config->get_dir("Dir::State::lists");
}

# Path to dpkg status file
my $status_file = $opts{'status-file'} || "/var/lib/dpkg/status";
my @files;
my $filesref;

my %used_suites = ();
# Determine the release names currently used by this host.
# %releasenames structure example:
# ('ftp.de.debian.org_debian_dists_unstable' => {'Suite'    => 'unstable',
#                                                'Name'     => 'unstable',
#                                                'Codename' => 'sid'},
#  'debian.udsorg.ru_dists_unstable'         => {'Suite'    => 'unknown',
#                                                'Name'     => 'unknown',
#                                                'Codename' => 'unknown'},
#  ...)
my %releasenames = &determine_releasenames();

if (exists $opts{'initialize'}) {
    unlink $apackagescachefile;
    unlink $ipackagescachefile;
    unlink $filescachefile;
}

# Get Packages-files list from cache or create new list and write
# cache if root
if (-e $filescachefile and -M $filescachefile < -M $list_dir) {
    $filesref = retrieve($filescachefile);
    @files = @$filesref unless !ref($filesref);
}
# Test also to be sure $filescachefile is not corrupt and returns a ref to it
if (!-e $filescachefile or -M $list_dir < -M $filescachefile or !ref($filesref)) {
    opendir(DIR, $list_dir) or &die("Can't opendir $list_dir: $!\n");
    @files = split(/\s/, `apt-get indextargets -o Dir::State::lists=${list_dir} --format='\$(FILENAME)' 'Created-By: Packages'`);
    ($< == 0) and (nstore(\@files, $filescachefile) or
        warn "Can't write $filescachefile\n");
    ($< == 0) and (chmod($cachefilemode, $filescachefile) or
        warn "Can't chmod $filescachefile\n");

    closedir DIR ;
}
unless (@files > 0) {
    &die("Error: No information about packages! (Maybe no deb entries?)\n");
}

# Get hash with all installed packages from cache or create new hash
# and write cache if root
# $ipackages structure example:
# {'dblatex' => {'amd64' => {'Version' => '0.2.8-6',
#                            'Status' => 'install ok installed',
#                            'Package' => 'dblatex'}},
#  ...}
my $ipackages;

if (-e $ipackagescachefile and -M $ipackagescachefile < -M $status_file) {
    $ipackages = retrieve($ipackagescachefile);
}
if (!-e $ipackagescachefile or -M $status_file < -M $ipackagescachefile or !ref($ipackages)) {
    ($ipackages, undef) = parse_file ($status_file, 1);
    ($< == 0) and (nstore($ipackages, $ipackagescachefile) or
        warn "Can't write $ipackagescachefile\n");
    ($< == 0) and (chmod($cachefilemode, $ipackagescachefile) or
        warn "Can't chmod $ipackagescachefile\n");
}

# Get available packages list from cache if possible
# $apackages structure example:
# {'dblatex' => {'amd64' => {'ftp.de.debian.org_debian_dists_stable'
#                             => {'Version' => '0.2-2',
#                                 'Release' => 'ftp.de.debian.org_debian_dists_stable',
#                                 'Package' => 'dblatex'},
#                            'ftp.de.debian.org_debian_dists_testing'
#                             => {'Version' => '0.2.8-2',
#                                 'Release' => 'ftp.de.debian.org_debian_dists_testing',
#                                 'Package' => 'dblatex'},
#                            'ftp.de.debian.org_debian_dists_unstable'
#                             => {'Version' => '0.2.8-6',
#                                 'Release' => 'ftp.de.debian.org_debian_dists_unstable',
#                                 'Package' => 'dblatex'}}},
#  ...}
my $apackages;
my $cache_file_corrupt;
-e $apackagescachefile and $apackages = retrieve($apackagescachefile);
unless (ref($apackages)) {
    $cache_file_corrupt = 1;
    undef $apackages;
}

my $default_release;

$default_release = $_config->get("APT::Default-Release");

my @official_suites = qw(oldstable stable proposed-updates stable-updates testing testing-proposed-updates testing-updates unstable experimental);
# %official_suites:
# - Keys:   Known official suite names
# - Values: Order index
my %official_suites;
$official_suites{$official_suites[$_]} = $_ foreach (0 .. $#official_suites);

# Get available package information out of all Packages files
foreach (@files) {
    # Parse Packages file if creation time is newer than packages cache
    if (! -e $apackagescachefile or -C $_ < -M $apackagescachefile
        or $cache_file_corrupt) {
        my ($href, $release) = &parse_file ($_);
        foreach my $pkg (keys %$href) {
	    foreach my $arch (keys %{$href->{$pkg}}) {
                $apackages->{$pkg}{$arch}{$release} = $href->{$pkg}{$arch} if
		    (!defined $apackages->{$pkg}{$arch}{$release} ||
		     $vs->compare($apackages->{$pkg}{$arch}{$release}{$VERS},
				  $href->{$pkg}{$arch}{$VERS}) < 0);
            }
	}
    }
}
# Storable.pm now has a hash limit which is too small for us
if (defined $Storable::recursion_limit_hash) {
    $Storable::recursion_limit_hash = -1;
}
# Store if we are root
($< == 0) and (nstore($apackages, $apackagescachefile) or
               &die("Warning: Can't write to $apackagescachefile!\n"));
($< == 0) and (chmod($cachefilemode, $apackagescachefile));

# Exit if we are root and using the -i option
($< == 0) and (exists $opts{'initialize'}) and exit;

# print info for selected package
if ($mode == $MODE_SINGLE) {
    my $key = $opts{'package'};

    print_package ($key);
}
elsif ($mode == $MODE_MULTIPLE) {
    print_package($_) foreach (sort keys %pkg_names);
}
else {
    # print info for all packages or packages matching regex
    my $pkgs = ($opts{'regex-all'}) ? $apackages : $ipackages;
    foreach my $key (sort keys %$pkgs) {
        next if (exists $opts{'package'} &&
                 exists $opts{'regex'} &&
                 !($key =~ m/$opts{'package'}/));
        print_package ($key);
    }
}

################################################################################
# Collect uptodate or up/downgradeable status of package depending on
# distribution.  Return: ($version_indicator, @version_info)
# - $version_indicator:
#   * 0: Version is not to be installed/kept.
#   * 1: Version is to be kept.
#   * 2: Version is to be up/downgraded.
# - @version_info:
#   Version information to be printed (undef if no information exists)
################################################################################
sub print_version {
    my ($archiv, $pkgarch, $iversion, $aversion, $cand) = @_;

    if (defined($aversion) and $cache->{$pkgarch}) {
        if ($cand and $aversion eq $cand->{VerStr})
        {
            my $cmp_versions = $vs->compare($aversion, $iversion);
            if ($cmp_versions != 0) {
                my $direction = ($cmp_versions > 0) ? 'up' : 'down';
                return(2, "$pkgarch/$archiv",
                       (defined($opts{'brief'})) ? "\n" :
                       " $iversion ${direction}gradeable to $aversion\n");
            }
            else {
                return(1, "$pkgarch/$archiv", defined($opts{'brief'}) ? "\n"
                       : " $iversion uptodate\n");
            }
        }
    }
    # Default outcome: either version is definitely not to be installed/kept
    #                  or information for a decicion is lacking.
    return(0, undef);
}

# print information about package

sub print_package {
    my ($package) = @_;
    my ($pkgname, $archname);

    if ($package =~ m/:/) {
        ($pkgname, $archname) = split /:/, $package;
    } else {
        $pkgname = $package;
    }
    
    my $pkgs = ($opts{'regex-all'}) ? $apackages : $ipackages;

    if ($archname and ! defined $apackages->{$pkgname}{$archname}) {
        printf("%s not available for architecture %s\n", $pkgname, $archname);
    } elsif (! defined $pkgs->{$pkgname}) {
        if ($archname) {
	    print_package_internal($pkgname, $archname)
        } elsif (keys(%{$apackages->{$pkgname}})) {
            my $archlist = "";
            foreach my $a (sort keys(%{$apackages->{$pkgname}})) {
		print_package_internal($pkgname, $a);
                $archlist .= ($archlist ? ", $a" : "$a");
            }
        } else {
            printf("%s not installed (not available)\n", $pkgname);
        }
    } else {
        foreach my $arch ($archname or sort keys(%{{map{$_=>1}(keys(%{$apackages->{$pkgname}}), keys(%{$pkgs->{$pkgname}}))}})) {
            print_package_internal($pkgname, $arch);
        }
    }
}

sub print_package_internal {
    my ($package, $arch) = @_;
    my $pkgarch = $package . ":" . $arch;

    # Sort all releases of package.
    my @pkg_releases = sort sort_pkg_releases values(%{$apackages->{$package}{$arch}});

    # All print information of package must be buffered, as the decision
    # whether to suppress all printing for the package can be executed only at
    # a later stage.
    my @print_info = ();
    my $is_upgradeable = 0;  # Intialize with: not upgradeable.
    # To guarantee tabular printing of the package's releases some further
    # variables are needed:
    my $max_package_len = 0;
    my $max_version_len = 0;
    my $max_name_len = 0;
    my $ipkg = $ipackages->{$package}{$arch};

    # print more information if required
    if ($opts{'allversions'}) {
        if ($ipkg->{$PACKAGE}) {
            push @print_info, "$ipkg->{$PACKAGE}:$ipkg->{$ARCH} ";
            unless ($ipkg->{$STATUS} =~ /not-installed/ ||
                $ipkg->{$STATUS} =~ /config-files/) {
                push @print_info, "$ipkg->{$VERS} ";
            }
            push @print_info, "$ipkg->{$STATUS}\n";
        }

        # Index to @official_suites: Next official suite to mention if missing.
        my $official_idx = 0;
        # Print preparation loop
        foreach my $pkg (@pkg_releases) {
            # First handle missing official suites to be listed before current
            # release.
            my $cur_idx = $official_suites{&get_rel_suite($pkg->{$RELEASE})};
            if (defined $cur_idx) {
                # Current release is an official one:
                # List prepending missing suites.
                foreach ($official_idx .. $cur_idx - 1) {
                    if ($used_suites{$official_suites[$_]}) {
                        push @print_info, "No $official_suites[$_] version\n";
                    }
                }
                # All official suites including current one are handled.
                $official_idx = $cur_idx + 1;
            }
            # Then handle current release.
            (my $archive = $pkg->{$RELEASE}) =~ s/_.*//;
            my $pa = $pkg->{$PACKAGE} . ":" . $pkg->{$ARCH};
            push @print_info, {$PACKAGE => $pa,
                               $VERS => $pkg->{$VERS},
                               $NAME => &get_rel_name($pkg->{$RELEASE}),
                               $ARCHIVE => $archive};
            $max_package_len = &max(length($pa), $max_package_len);
            $max_version_len = &max(length($pkg->{$VERS}), $max_version_len);
            $max_name_len = &max(length(&get_rel_name($pkg->{$RELEASE})),
                                 $max_name_len);
        }
        # Finally handle missing official suites after last existing release.
        foreach ($official_idx .. $#official_suites) {
            if ($used_suites{$official_suites[$_]}) {
                push @print_info, "No $official_suites[$_] version\n";
            }
        }
    }

    my $iversion = $ipkg->{$VERS};

    # print info about upgrade status (only if package is installed)

    if (($ipkg->{$VERS}) &&
        (!($ipkg->{$STATUS} =~ /config-files/))) {
        # Reorder package version structures to prefer the default release.
        @pkg_releases = &reorder_pkg_releases(@pkg_releases);
        my $found = 0;
        my $aversion = 0;
        my $cand;
        if ($cache->{$pkgarch}) {
            $cand = $policy->candidate($cache->{$pkgarch});
        }
	my $irelease; # first release associated with $iversion in reorder_pkg_releases() order.
	foreach (@pkg_releases) {
	    if ( $_->{$VERS} eq $iversion ) {
		$irelease = &get_rel_name($_->{$RELEASE});
		last;
	    }
	}
        foreach (@pkg_releases) {
            my $version = $_->{$VERS};
            if ($version) {
                my @version_info;
                ($found, @version_info) =
		    &print_version(($irelease ? $irelease : &get_rel_name($_->{$RELEASE})),
                                   $pkgarch, $iversion, $version, $cand);
                push @print_info, @version_info if ($found);
                $aversion = $version;
            }
            $is_upgradeable = 1 if ($found == 2);
            last if $found;
        }
        if ($aversion && ($vs->compare($iversion, $aversion) > 0)) {
            # Test whether installed version is newer
            # than all available versions.
            my $newer_indic = 1;
            foreach (@pkg_releases) {
                my $cmp_version = $_->{$VERS};
                if ($cmp_version and
                    $vs->compare($iversion, $cmp_version) <= 0)
                {
                    $newer_indic = 0;
                    last;
                }
            }
            if ($newer_indic and not defined($opts{'brief'}))
            {
                push(@print_info,
                     "$pkgarch $iversion newer than version in archive\n");
            }
        } elsif (not $found) {
            # Check for manual upgrade possibility:
            # There are cases where the APT policy doesn't find a better
            # candidate than the installed version, but which itself isn't
            # available any longer because it has been replaced by a newer
            # version in the archives.  As the newer version isn't chosen by
            # the policy, the upgrade can only be executed manually.
            if ($cand and $iversion eq $cand->{VerStr}) {
                foreach my $release (@pkg_releases) {
                    my $cmp_version = $release->{$VERS};
                    if ($cmp_version and
                        $vs->compare($iversion, $cmp_version) < 0)
                    {
                        push(@print_info,
                             $pkgarch,
                             '/',
                             &get_rel_name($release->{$RELEASE}),
                             (defined($opts{'brief'})) ? "\n" :
                             " *manually* upgradeable from $iversion to " .
                             "$aversion\n");
                        $found = 1;
                        $is_upgradeable = 1;
                        last;
                    }
                }
            }
            if (not $found) {
                push(@print_info, "$pkgarch $iversion installed: No available ",
                     "version in archive\n");
            }
        }
    } else {
        push(@print_info, "$pkgarch not installed",
             ($mode == $MODE_SINGLE and not keys(%{$apackages->{$package}{$arch}}))
            ? " (even not available)\n" : "\n");
    }

    if ($opts{'upgradeable'}
        and not $is_upgradeable
        and $mode == $MODE_SINGLE) {
        # Caller expects single given package to be upgradeable.
        # Signal failure of this expectation with a special exit code.
        exit 2;
    }

    # Print loop
    unless ($opts{'upgradeable'} and not $is_upgradeable) {
        foreach my $print_info (@print_info) {
            if (ref $print_info) {
                printf("%*s %*s %*s %s\n",
                       -$max_package_len, $print_info->{$PACKAGE},
                       -$max_version_len, $print_info->{$VERS},
                       -$max_name_len, $print_info->{$NAME},
                       $print_info->{$ARCHIVE});
            }
            else {
                print $print_info;
            }
        }
    }
}

# ------------------------------------------------------
# FUNCTION: HASHREF, RELEASE_KEY = parse_file FILE (STATUS)
#
# Parses FILE into an HASHREF of Hashes
# Set STATUS when the file should be parsed just for
# installed packages (here the dpkg status file)
# Returns HASHREF and key of corresponding %releasenames record.
# ------------------------------------------------------

sub parse_file {
    my ($file, $status) = @_;
    my ($key, $value, $package, $packages);

    my $release = &determine_pkgfile_release($file);
    open FILE, "/usr/lib/apt/apt-helper cat-file $file|" or &die("Can't open file $file: $!\n");
    if ($opts{'verbose'}) {print "Parsing $file...";};
    while (<FILE>) {
        if (/^$/){
            unless (defined $package and
		    defined $package->{$PACKAGE} and
		    defined $package->{$ARCH} ) {next};

            if ($status) { # Are we parsing the status file?
                # if we did not specify a package or pattern
                # only include installed packages
                unless ($mode == $MODE_ALL and
                        ($package->{$STATUS} =~ /not-installed|config-files/ or
                         # don't print holded packages if requested
                         ($opts{'nohold'} and $package->{$STATUS} =~ /hold/))) {
                    $packages->{$package->{$PACKAGE}}{$package->{$ARCH}} = $package;
                }
            }
            else {
                if (!defined $packages->{$package->{$PACKAGE}} or
		    !defined $packages->{$package->{$PACKAGE}}{$package->{$ARCH}}{$VERS} or
                    $vs->compare($packages->{$package->{$PACKAGE}}{$package->{$ARCH}}{$VERS},
			 $package->{$VERS}) < 0) {
                    $package->{$RELEASE} = $release;
                    $packages->{$package->{$PACKAGE}}{$package->{$ARCH}} = $package;
                }
            }
            undef $package;
            next;
        }
        unless ((/^Package/) || (/^Version/) || (/^Status/) || (/^Source/) || (/^Architecture/)) {next};
        ($key, $value) = split /: /, $_;
        $value =~ s/\n//;
        $value =~ s/\s\(.*\)$//; # Remove any Version information in ()
        $package->{$key} = $value;
    }
    if ($opts{'verbose'}) {print " completed.\n"};
    close FILE;
    return $packages, $release;
}

################################################################################
# Determine the release of the specified package file.
# If no corresponding %releasenames record exists, one gets created.
# Argument $pkgfile is either full package file name or name core, e.g.:
# - /var/lib/apt/lists/ftp.de.debian.org_debian_dists_unstable_main_binary-i386_Packages
# - ftp.de.debian.org_debian_dists_unstable
################################################################################
sub determine_pkgfile_release {
    my $pkgfile = shift;

    return $pkgfile if ($releasenames{$pkgfile});
    $pkgfile =~ s{.*/}{};
    return undef if ($pkgfile eq 'status');
    # Sort according to length so we make the most specfic match
    foreach (sort { length($b) <=> length($a) } keys %releasenames) {
        return $_ if ($_ eq substr($pkgfile, 0, length($_)));
    }
    # As package file has no release file, create a fallback %releasenames
    # record based on the information of the package file name.
    my $releasename;
    foreach my $suite (@official_suites) {
        if (index($pkgfile, "_${suite}_") != -1) {
            # Packagefile belongs to a known suite.
            ($releasename = $pkgfile) =~ s/(.*$suite).*/$1/;
            $releasenames{$releasename}{$SUITE} = $suite;
            $releasenames{$releasename}{$NAME} = $suite;
            last;
        }
    }
    unless ($releasename) {
        # No release information available for this package file:
        # create a dummy %releasenames record.
        $releasename = $pkgfile;
        $releasenames{$releasename}{$SUITE} = $UNKNOWN;
        $releasenames{$releasename}{$NAME} = $UNKNOWN;
    }
    $releasenames{$releasename}{$CODENAME} = $UNKNOWN;
    return $releasename;
}

################################################################################
# Determine the release names currently used by this host.
################################################################################
sub determine_releasenames {
    my %rel_names;
    opendir LIST_DIR, $list_dir
        or &die("Failed to open directory $list_dir: $!\n");
    while (defined(my $rel_file = readdir LIST_DIR)) {
        my $file_name = "$list_dir/$rel_file";
        if ($rel_file =~ m/(.*)_(In|)Release$/) {
            $rel_file = $1;
        }
        else {
            next;
        }
        open RELEASE_FILE, "< $file_name"
            or &die("Failed to open file $file_name for reading: $!\n");
        while (defined (my $line = <RELEASE_FILE>)) {
            if ($line =~ m/^\s*($SUITE|$CODENAME):\s*(\S+)\s*$/o) {
                $rel_names{$rel_file}{$1} = $2;
            }
            # After extracting values for Suite and Codename, do not parse
            # rest of release file.
            # Thus normally only the first lines of the release file must be
            # read, whereas the much bigger rest may be skipped.
            if (defined $rel_names{$rel_file}{$SUITE} and
                defined $rel_names{$rel_file}{$CODENAME}) {
                last;
            }
        }
        close RELEASE_FILE
            or &die("Failed to close file $file_name: $!\n");
        # Register suite as used.
        if (defined $rel_names{$rel_file}{$SUITE}) {
            $used_suites{$rel_names{$rel_file}{$SUITE}} = 1;
        }
        # Provide default values for missing fields.
        foreach ($SUITE, $CODENAME) {
            unless (defined $rel_names{$rel_file}{$_}) {
                $rel_names{$rel_file}{$_} = $UNKNOWN;
            }
        }
        # Determine name relevant to user (as used in sources.list):
        # either Suite or Codename.
        if ($rel_file =~ m/_$rel_names{$rel_file}{$SUITE}/) {
            $rel_names{$rel_file}{$NAME} = $rel_names{$rel_file}{$SUITE};
        }
        elsif ($rel_file =~ m/_$rel_names{$rel_file}{$CODENAME}/) {
            $rel_names{$rel_file}{$NAME} = $rel_names{$rel_file}{$CODENAME};
        }
        else {
            # Fall back to Suite.
            $rel_names{$rel_file}{$NAME} = $rel_names{$rel_file}{$SUITE};
        }
    }
    closedir LIST_DIR
        or &die("Failed to close directory $list_dir: $!\n");
    return %rel_names;
}

################################################################################
# Return the numerically biger of the two specified arguments.
################################################################################
sub max {
    return ($_[0] > $_[1]) ? $_[0] : $_[1];
}

################################################################################
# Reorder package releases in a way that within the releases of the same
# version number the default release gets placed first.
################################################################################
sub reorder_pkg_releases {
    my @releases = @_;

    if (@releases and $default_release) {
        # Reordering strategy:
        # - Precondition: The releases are sorted by version already.
        # - Iterate over the release list: from "left" to "right".
        # - For the releases of each version:
        #   - Find the first release that is not the default release.
        #   - If right from this "move candidate" the default release is found,
        #     move it left before the move candidate.
        my $move_idx;  # Index of move candidate
        foreach my $idx (0 .. $#releases) {
            my $rel_key = $releases[$idx]->{$RELEASE};
            if (defined $move_idx) {
                # There exists a move candidate.
                if ($releases[$idx]->{$VERS} eq $releases[$move_idx]->{$VERS}) {
                    # Current release is of same version as move candidate.
                    if (&get_rel_suite($rel_key) eq $default_release
                        or &get_rel_codename($rel_key) eq $default_release) {
                        # Move current release before move candidate in order to
                        # place default release first.
                        my $rel = splice @releases, $idx, 1;
                        splice @releases, $move_idx, 0, $rel;
                        $move_idx = $idx;
                    }
                }
                else {
                    # Version change
                    undef $move_idx;
                }
            }
            unless (defined $move_idx) {
                # Test whether current release is move candidate.
                if (&get_rel_suite($rel_key) ne $default_release
                    and &get_rel_codename($rel_key) ne $default_release) {
                    $move_idx = $idx;
                }
            }
        }
    }
    return @releases;
}

################################################################################
# Sorting function for package releases
# Sorting hierarchy:
# 1) Release number
# 2) @official_suites (in array order) before other ones
# 3) Release name
################################################################################
sub sort_pkg_releases {
    my $cmp_versions = $vs->compare($a->{$VERS}, $b->{$VERS});
    return $cmp_versions if ($cmp_versions);
    my $cmp_suites = (&suite_idx(&get_rel_suite($a->{$RELEASE})) <=>
                      &suite_idx(&get_rel_suite($b->{$RELEASE})));
    return $cmp_suites if ($cmp_suites);
    return(&get_rel_name($a->{$RELEASE}) cmp &get_rel_name($b->{$RELEASE}));
}

################################################################################
# Return the sorting index of the specified suite name.
# Unofficial suites are sorted last.
################################################################################
sub suite_idx {
    return(defined($official_suites{$_[0]}) ? $official_suites{$_[0]}
           : $#official_suites + 1);
}

################################################################################
# Simple die wrapper which controls the exit code.
# If first parameter is a number, it is used as the exit code.  Otherwise it
# gets interpreted (like the remaining parameters) as the error message.
################################################################################
sub die {
    $! = ($_[0] =~ m/^\d+$/) ? shift() : 255;
    die @_;
}

################################################################################
# Access function for the fields of the %releasenames structure
# Missing fields are augmented on the fly (compare BTS report #515328).
################################################################################
sub get_rel_codename {
    my $rel_key = shift;
    &determine_pkgfile_release($rel_key) unless $releasenames{$rel_key};
    return $releasenames{$rel_key}{$CODENAME};
}
sub get_rel_name {
    my $rel_key = shift;
    &determine_pkgfile_release($rel_key) unless $releasenames{$rel_key};
    return $releasenames{$rel_key}{$NAME};
}
sub get_rel_suite {
    my $rel_key = shift;
    &determine_pkgfile_release($rel_key) unless $releasenames{$rel_key};
    return $releasenames{$rel_key}{$SUITE};
}

# script documentation (POD style)

=encoding utf8

=head1 NAME

apt-show-versions - Lists available package versions with distribution

=head1 DESCRIPTION

apt-show-versions parses the dpkg status file and the APT lists for
the installed and available package versions and distribution and
shows upgrade options within the specific distribution of the selected
package.

This is really useful if you have a mixed stable/testing environment
and want to list all packages which are from testing and can be
upgraded in testing.

apt-show-versions uses caching for the status information of installed
and available packages. If you run apt-show-versions as root the
cache is updated as needed. If you run as non-root uses the newest
available information, but can't update the cache. If you run as root
with the option B<-i> the cache is initialized or updated only.

=head1 SYNOPSIS

B<apt-show-versions> [B<-h>] [[B<-p>] I<package name>] [B<-a>] [B<-b>]

=head1 OPTIONS

If you don't give any options the status of all installed packages is
printed.

=over 4

=item B<-p> I<package>, B<--package>=I<package>

Print available and installed versions for specified I<package>. You
can also specify a package name without the option B<-p>. If B<-p> and
a package name are missing, all installed packages are displayed.

=item B<-r>, B<--regex>

interpret I<package> from option B<-p> as a regex.

=item B<-R>, B<--regex-all>

like B<--regex>, but also show matching packages which are not installed

=item B<-u>, B<--upgradeable>

Print only upgradeable packages

=item B<-a>, B<--allversions>

Print all available versions of the selected packages

=item B<-b>, B<--brief>

Print only package_name/distribution for upgradeable packages

=item B<-v>, B<--verbose>

Prints out messages about which package files are parsed.

=item B<-V>, B<--version>

Prints out version of apt-show-versions

=item B<-i>, B<--initialize>

Initialize or update package cache only (as root). Do this every time
when the status of the installed or available packages has
changed. Initialization is done automatically on installation of the
package and via a cron.daily job.

=item B<-stf> I<file>, B<--status-file>=I<file>

Use I<file> as the dpkg status file instead of /var/lib/dpkg/status

=item B<-ld> I<directory>, B<--list-dir>=I<directory>

Use I<directory> as path to apt's list files instead of
/var/state/apt/lists/ or /var/lib/apt/lists/

=item B<-h>, B<--help>

Prints out command-line help.

=back

=head1 EXIT CODES

=over 4

=item C<0>

No error

=item C<1>

Wrong usage

=item C<2>

apt-show-versions has been called with exactly one package and upgradeable
option set, but package is uptodate. As no output has been requested, this
case gets signaled using the exit code.

=item C<255>

Unspecified error

=back

=head1 EXAMPLES

If you want to know for all your installed packages whether they are
uptodate or upgradeable, use:

    apt-show-versions

If you want to have a list of all upgradeable packages:

    apt-show-versions -u

To get a list of all available versions of libc6:

    apt-show-versions -a -p libc6

To get information about several packages:

    apt-show-versions dpkg apt

    apt-show-versions -r ^texlive

To upgrade all packages in testing:

    apt-get install `apt-show-versions -u -b | grep testing`

=head1 AUTHOR

Christoph Martin, martin@uni-mainz.de

=head1 SEE ALSO

apt(8), dpkg(1)

=cut