#!/usr/bin/env perl
## Copyright (C) 2008 by Daniel Friesel <derf@derf.homelinux.org>
## License: WTFPL <http://sam.zoy.org/wtfpl>
use strict;
use warnings;
use AptPkg::Cache;
use Switch;
use Getopt::Long;

my $cache = AptPkg::Cache->new;
my $not = 0;
GetOptions(
	"not" => \$not,
);
my $packagename = shift or die("No packagename given");
my $package = $cache->{$packagename};

unless($package) {
	print STDERR "E: Package not found: $packagename\n";
	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};
	}
}

print "State: $package->{CurrentState}\n";
if ($package->{Flags} =~ /Essential/) {
	print "Essential: yes\n";
}

if ($not) {
	print_deps(why_not($package->{RevDependsList}));
} else {
	print_deps(why($package->{RevDependsList}));
}

__END__

=head1 NAME

apt-why - filtered reverse dependency displayer using AptPkg::Cache

=head1 SYNOPSIS

B<apt-why> [ B<--not> ] I<package>

=head1 DESCRIPTION

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

The output is prefixed by two charactes, the former representing the desired
package state, the latter the current state.

The states are I<i>nstall, I<h>old, I<r>emove (deinstall), I<p>urge,
I<u>npacked, halI<f> configured, I<h>alf installed, I<c>onfigfiles installed.
An empty field means not installed.

If B<--not> is specified, reverse dependencies prohibiting the installation of
I<package> are shown. Else, reverse dependencies justifying the installation
of I<package> are shown

=head1 AUTHOR

Daniel Friesel <derf@derf.homelinux.org>

=head1 LICENSE

  0. You just DO WHAT THE FUCK YOU WANT TO.