#!/usr/bin/env perl
use strict;
use warnings;
use AptPkg::Cache;
use Switch;

my $cache = AptPkg::Cache->new;
my $query = shift or die("No action given");
my $packagename = shift or die("No packagename given");
my $package = $cache->{$packagename};

unless($package) {
	print "E: Package not found: $packagename";
	exit(100);
}

sub revdeps {
	my $rdepsref = shift;
	my $depsref;
	my $parent;

	foreach(@$rdepsref) {
		undef($parent);
		$parent->{name} = $_->{ParentPkg}{Name};
		$parent->{ver} = $_->{ParentVer}{VerStr};
		$parent->{current_state} = $cache->{$_->{ParentPkg}{Name}}->{CurrentState};
		$parent->{selected_state} = $cache->{$_->{ParentPkg}{Name}}->{SelectedState};
		$parent->{deptype} = $_->{DepType};
		$parent->{targetname} = $_->{TargetPkg}{Name};
		if ($_->{TargetVer}) {
			$parent->{depsign} = $_;
			$parent->{depver} = $_;
		}
		$depsref->{$parent->{name}} = $parent;
	}
	return($depsref);
}

sub why {
	my $revdeps = revdeps(shift);
	my $why;
	foreach(keys(%$revdeps)) {
		if ($revdeps->{$_}->{current_state} eq 'Installed' and $revdeps->{$_}->{deptype} !~ /^(Conflicts|Replaces|Obsoletes)$/) {
			$why->{$_} = $revdeps->{$_};
		}
	}
	return($why);
}

sub why_not {
	my $revdeps = revdeps(shift);
	my $why_not;
	foreach(keys(%$revdeps)) {
		if ($revdeps->{$_}->{current_state} eq 'Installed' and $revdeps->{$_}->{deptype} =~ /^(Conflicts|Replaces|Obsoletes)$/) {
			$why_not->{$_} = $revdeps->{$_};
		}
	}
	return($why_not);
}

sub short_states {
	my $pkg = shift;
	my $state = '';
	switch($pkg->{selected_state}) {
		case('Unkwnon') {
			$state .= ' ';
		} case('Install') {
			$state .= 'i';
		} case('Hold') {
			$state .= 'h';
		} case('DeInstall') {
			$state .= 'r';
		} case('Purge') {
			$state .= 'p';
		}
	}
	switch($pkg->{current_state}) {
		case('Installed') {
			$state .= 'i';
		} case('UnPacked') {
			$state .= 'u';
		} case('HalfConfigured') {
			$state .= 'f';
		} case('HalfInstalled') {
			$state .= 'h';
		} case('ConfigFiles') {
			$state .= 'c';
		} case('NotInstalled') {
			$state .= ' ';
		}
	}
	return($state);
}


sub print_deps {
	my $deps = shift;
	foreach(keys(%$deps)) {
		printf "%-2s  %-30s %-15s %s\n", short_states($deps->{$_}), $deps->{$_}->{name}, $deps->{$_}->{deptype}, $deps->{$_}->{targetname};
	}
}

if ($query eq 'why') {
	print_deps(why($package->{RevDependsList}));
} elsif ($query eq 'why-not') {
	print_deps(why_not($package->{RevDependsList}));
} elsif ($query eq 'rdeps') {
	print_deps(revdeps($package->{RevDependsList}));
}

__END__

=head1 NAME

apt-perl - reverse dependency displayer using ApgPkg::Cache

=head1 SYNOPSIS

apt-perl I<command> I<package>

=head1 DESCRIPTION

B<apt-perl> displays various informations based on a I<package>s reverse
dependencies

I<command> may be one of:

=over

=item why

Show dependencies that justify the installation of a package

=item why-not

Show dependencies that prohibit the installation of a package

=item rdeps

Show all reverse dependencies of a package

=back