#!/usr/bin/perl -w

=head1 NAME

dh_installsystemduser - install systemd unit files

=cut

use strict;
use warnings;
use Debian::Debhelper::Dh_Lib;

my $deb_host_arch_os = dpkg_architecture_value('DEB_HOST_ARCH_OS');
if ($deb_host_arch_os ne 'linux')
{
    warning("systemd is unsupported on $deb_host_arch_os, doing nothing");
    exit(0);
}

our $VERSION = DH_BUILTIN_VERSION;

=head1 SYNOPSIS

B<dh_installsystemduser> [S<I<debhelper options>>] [B<--no-enable>] [B<--name=>I<name>] [S<I<unit file> ...>]

=head1 DESCRIPTION

B<dh_installsystemduser> finds the systemd user instance service files
installed by a package and generates F<postinst>, and F<prerm> code
blocks for enabling and disabling the corresponding systemd user
instance services, when the package is installed, updated, or
removed. These snippets are added to the maintainer scripts by
L<dh_installdeb(1)>.

L<deb-systemd-helper(1)> is used to enable and disable the systemd
units, thus it is not necessary that the machine actually runs systemd
during package installation time, enabling happens on all machines.

B<dh_installsystemduser> operates on all user instance unit files
installed by a package. For only generating blocks for specific unit
files, pass them as arguments. Specific unit files can be excluded
from processing using the B<-X> common L<debhelper(1)> option.

=head1 FILES

=over 4

=item debian/I<package>.user.path,
      debian/I<package>@.user.path,
      debian/I<package>.user.service,
      debian/I<package>@.user.service,
      debian/I<package>.user.socket,
      debian/I<package>@.user.socket,
      debian/I<package>.user.target,
      debian/I<package>@.user.target,
      debian/I<package>.user.timer,
      debian/I<package>@.user.timer

If any of those files exists, they are installed into
F<usr/lib/systemd/user/> in the package build directory removing the
F<.user> file name part.

=back

=head1 OPTIONS

=over 4

=item B<--name=>I<name>

Install the service file as I<name.service> instead of the default
filename I<package.service>. When this parameter is used,
B<dh_installsystemd> looks for and installs files named
F<debian/package.name.user.service> instead of the usual
F<debian/package.user.service>.  Moreover, maintainer scripts are only
generated for units that match the given I<name>.

=item B<--no-enable>

Disable the service(s) on purge, but do not enable them on install.

=back

=head1 NOTES

This command is not idempotent. L<dh_prep(1)> should be called between
invocations of this command (with the same arguments). Otherwise, it
may cause multiple instances of the same text to be added to
maintainer scripts.

=cut

# PROMISE: DH NOOP WITHOUT tmp(usr/lib/systemd/user) user.service

init(options => {
	"no-enable" => \$dh{NO_ENABLE},
});

sub quote {
	# Add single quotes around the argument.
	return '\'' . $_[0] . '\'';
}

sub uniq {
	my %seen;
	return grep { !$seen{$_}++ } @_;
}

sub contains_install_section {
	my ($unit_path) = @_;

	open(my $fh, '<', $unit_path) or error("Cannot open($unit_path) to check for [Install]: $!");

	while (my $line = <$fh>) {
		chomp($line);
		return 1 if $line =~ /^\s*\[Install\]$/i;
	}
	close($fh);
	return 0;
}

sub install_user_unit {
	my ($package, $name, $suffix) = @_;

	my $tmpdir = tmpdir($package);
	my $path = "$tmpdir/usr/lib/systemd/user";
	my $unit = pkgfile($package, "user.$suffix");
	return if $unit eq '';

	install_dir($path);
	install_file($unit, "$path/$name.$suffix");
}

# Extracts the directive values from a unit file. Handles repeated
# directives in the same unit file. Assumes values can only be
# composed of lists of unit names. This is good enough for the 'Also='
# and 'Alias=' directives handled here.
sub extract_key {
	my ($unit_path, $key) = @_;
	my @values;

	open(my $fh, '<', $unit_path) or error("Cannot open($unit_path): $!");

	while (my $line = <$fh>) {
		chomp($line);

		# Since unit names can't have whitespace in systemd, simply
		# use split and strip any leading/trailing quotes. See
		# systemd-escape(1) for examples of valid unit names.
		if ($line =~ /^\s*$key=(.+)$/i) {
			for my $value (split(/\s+/, $1)) {
				$value =~ s/^(["'])(.*)\g1$/$2/;
				push @values, $value;
			}
		}
	}

	close($fh);
	return @values;
}

sub list_installed_user_units {
	my ($tmpdir, $aliases) = @_;

	my $lib_systemd_user = "$tmpdir/usr/lib/systemd/user";
	my @installed;

	return unless -d $lib_systemd_user;
	opendir(my $dh, $lib_systemd_user) or error("Cannot opendir($lib_systemd_user): $!");

	foreach my $name (readdir($dh)) {
		my $path = "$lib_systemd_user/$name";
		next unless -f $path;
		if (-l $path) {
			my $dest = basename(readlink($path));
			$aliases->{$dest} //= [ ];
			push @{$aliases->{$dest}}, $name;
		} else {
			push @installed, $name;
		}
	}

	closedir($dh);
	return @installed;
}

# Install package maintainer provided unit files.
foreach my $package (@{$dh{DOPACKAGES}}) {
	my $tmpdir = tmpdir($package);

	# unit file name
	my $name = $dh{NAME} // $package;

	for my $type (qw(service target socket path timer)) {
		install_user_unit($package, $name, $type);
		install_user_unit("${package}@", "${name}@", $type);
	}
}

# Generate postinst and prerm code blocks to enable and disable units
foreach my $package (@{$dh{DOPACKAGES}}) {
    my (@args, @enable_units, %aliases);

	my $tmpdir = tmpdir($package);
	my @units = list_installed_user_units($tmpdir, \%aliases);

	# Handle either only the unit files which were passed as arguments
	# or all unit files that are installed in this package.
	if (@ARGV) {
		@args = @ARGV;
	}
	elsif ($dh{NAME}) {
		# Treat --name flag as if the corresponding units were passed
		# in the command line.
		@args = grep /(^|\/)$dh{NAME}\.(service|target|socket|path|timer)$/, @units;
	}
	else {
		@args = @units;
	}

	# Support excluding units via the -X debhelper common option.
	foreach my $x (@{$dh{EXCLUDE}}) {
		@args = grep !/(^|\/)$x$/, @args;
	}

	# This hash prevents us from looping forever in the following
	# while loop.  An actual real-world example of such a loop is
	# systemd's systemd-readahead-drop.service, which contains
	# Also=systemd-readahead-collect.service, and that file in turn
	# contains Also=systemd-readahead-drop.service, thus forming an
	# endless loop.
	my %seen;

	# Must use while and shift because the loop alters the list.
	while (@args) {
		my $name = shift @args;
		my $path = "${tmpdir}/usr/lib/systemd/user/${name}";

		error("User unit file \"$name\" not found in package \"$package\".") if ! -f $path;

		# Skip template service files. Enabling or disabling those
		# services without specifying the instance is not useful.
		next if ($name =~ /\@/);

		# Handle all unit files specified via Also= explicitly. This
		# is not necessary for enabling, but for disabling, as we
		# cannot read the unit file when disabling as it has already
		# been deleted.
		push @args, $_ for grep { !$seen{$_}++ } extract_key($path, 'Also');

		push @enable_units, $name if contains_install_section($path);
	}

	@enable_units = map { quote($_) } sort(uniq(@enable_units));

	if (@enable_units) {
		# The generated maintainer script code blocks use the --user
		# option that was added to deb-systemd-helper in version 1.52.
		addsubstvar($package, 'misc:Depends', 'init-system-helpers', ">= 1.52");

		my $postinst = $dh{NO_ENABLE} ? 'postinst-systemd-user-dont-enable' : 'postinst-systemd-user-enable';
		foreach my $unit (@enable_units) {
			autoscript($package, 'postinst', $postinst, { 'UNITFILE' => $unit });
		}
		autoscript($package, 'postrm', 'postrm-systemd-user', { 'UNITFILES' => join(' ', @enable_units) });
	}
}

=head1 SEE ALSO

L<debhelper(7)>, L<dh_installsystemd(1)>, L<deb-systemd-helper(1)>

=head1 AUTHORS

pkg-systemd-maintainers@lists.alioth.debian.org

=cut