#!/bin/sh
# Copyright 2022 Helmut Grohne <helmut@subdivi.de>
# SPDX-License-Identifier: MIT

# shellcheck disable=SC2016 # Intentional quoting technique

: <<'POD2MAN'
=head1 NAME

debvm-create - Create a VM image for various Debian releases and architectures

=head1 SYNOPSIS

B<debvm-create> [B<-a> I<architecture>] [B<-h> I<hostname>] [B<-k> F<sshkey>] [B<-o> F<output>] [B<-r> I<release>] [B<-s> <task>] [B<-z> I<size_in_GB>] [B<--> I<mmdebstrap options>]

=head1 DESCRIPTION

B<debvm-create> is essentially a thin wrapper around B<mmdebstrap> for creating a raw ext4 filesystem image for booting with B<debvm-run>.
The purpose of these images primarily is testing the different releases and architectures without access to a physical machine of that architecture.
Beyond essential packages, the image will contain B<apt>, an init system and a suitable kernel package.
Notably absent is a bootloader and a partition table.
In order to boot such an image, one is supposed to extract the kernel and initrd from the image and pass it to a suitable bootloader.
No user account is created and root can login without specifying a password.

=head1 OPTIONS

=over 8

=item B<-a> I<architecture>, B<--architecture>=I<architecture>

Specify a Debian architecture name.
By default, the native architecture is being used.
A suitable kernel image is automatically selected and installed into the image.

=item B<-h> I<hostname>, B<--hostname>=I<hostname>

Set the hostname of the virtual machine.
By default, the hostname is B<testvm>.

=item B<-k> F<sshkey>, B<--sshkey>=F<sshkey>

Install the given ssh public key file into the virtual machine image for the root user.
This option also causes the ssh server to be installed.
By default, no key or server is installed.
To connect to the vm, pass a port number to B<debvm-run> with the B<-s> option.

=item B<-o> F<output>, B<--output>=F<output>

Specify the file name of the resulting virtual machine image.
By default, it is written to F<rootfs.ext4>.

=item B<-r> I<release>, B<--release>=I<release>

Use the given Debian release.
By default, B<unstable> is being used.

=item B<-s> I<task>, B<--skip>=I<task>

Skip a particular task or feature.
The option may be specified multiple times or list multiple tasks to be skipped by separating them with a comma.
By default, no tasks are skipped.
The following tasks may be skipped.

=over 4

=item B<kernel>

skips installing a linux kernel image.
This can be useful to install a custom kernel or to install a different kernel variant than is selected by default.

=item B<packagelists>

reduces the package lists inside the image.
The B<available> database for B<dpkg> is not created.
The package lists used by B<apt> are deleted.
This generally produces a smaller image, but you need to run B<apt update> before installing packages and B<dpkg --set-selections> does not work.

=item B<systemdnetwork>

skips installing B<libnss-resolve> as well as automatic network configuration via B<systemd-networkd>.

=item B<usrmerge>

By default B<debvm> adds a hook to enable merged-/usr without the B<usrmerge> package given a sufficiently recent Debian release.
Without the hook, dependencies will pull the B<usrmerge> package as needed, which may result in a larger installation.

=back

=item B<-z> I<size_in_GB>, B<--size>=I<size_in_GB>

Specify the minimum image size in giga bytes.
The resulting image will be grown as a sparse file to this size if necessary.
The default is 1 GB.

=item B<--> I<mmdebstrap options>

All options beyond a double dash are passed to B<mmdebstrap> after the suite and target specification.
This can be used to provide additional hooks for image customization.
You can also request additional packages to be installed into the image using B<mmdebstrap>'s B<--include> option.
Any positional arguments passed here will be treated as mirror specifications by B<mmdebstrap>.

=back

=head1 SEE ALSO

    debvm-run(1) mmdebstrap(1)

=cut
POD2MAN

set -u

ARCHITECTURE=$(dpkg --print-architecture)
IMAGE=rootfs.ext4
SIZE=$((1024*1024*1024))
SKIP=,
SSHKEY=
SUITE=unstable
VMNAME=testvm

SHARE_DIR="${0%/*}/../share"

nth_arg() {
	shift "$1"
	printf "%s" "$1"
}

die() {
	echo "$*" 1>&2
	exit 1
}
usage() {
	die "usage: $0 [-a architecture] [-h hostname] [-k sshkey] [-o output] [-r release] [-s task] [-z size_in_GB] [-- mmdebstrap options]"
}
usage_error() {
	echo "error: $*" 1>&2
	usage
}

opt_architecture() {
	ARCHITECTURE=$1
}
opt_hostname() {
	VMNAME=$1
}
opt_skip() {
	SKIP="$SKIP$1,"
}
opt_sshkey() {
	SSHKEY=$1
}
opt_output() {
	IMAGE=$1
	test "${IMAGE#-}" = "$IMAGE" || IMAGE="./$IMAGE"
}
opt_release() {
	SUITE=$1
}
opt_size() {
	SIZE=$(($1*1024*1024*1024))
}

while getopts :a:h:k:o:r:s:z:-: OPTCHAR; do
	case "$OPTCHAR" in
		a)	opt_architecture "$OPTARG"	;;
		h)	opt_hostname "$OPTARG"		;;
		k)	opt_sshkey "$OPTARG"		;;
		o)	opt_output "$OPTARG"		;;
		r)	opt_release "$OPTARG"		;;
		s)	opt_skip "$OPTARG"		;;
		z)	opt_size "$OPTARG"		;;
		-)
			case "$OPTARG" in
				help)
					usage
				;;
				architecture|hostname|output|release|size|skip|sshkey)
					test "$OPTIND" -gt "$#" && usage_error "missing argument for --$OPTARG"
					"opt_$OPTARG" "$(nth_arg "$OPTIND" "$@")"
					OPTIND=$((OPTIND+1))
				;;
				architecture=*|hostname=*|output=*|release=*|size=*|skip=*|sshkey=*)
					"opt_${OPTARG%%=*}" "${OPTARG#*=}"
				;;
				*)
					usage_error "unrecognized option --$OPTARG"
				;;
			esac
		;;
		:)
			usage_error "missing argument for -$OPTARG"
		;;
		'?')
			usage_error "unrecognized option -$OPTARG"
		;;
		*)
			die "internal error while parsing command options, please report a bug"
		;;
	esac
done
shift "$((OPTIND - 1))"

if test -n "$SSHKEY" && ! test -f "$SSHKEY"; then
	die "error: ssh keyfile '$SSHKEY' not found"
fi

check_skip() {
	case "$SKIP" in
		*",$1,"*)	return 0 ;;
		*)		return 1 ;;
	esac
}

case "$SUITE" in
	jessie)
		DEBVER=8
	;;
	stretch)
		DEBVER=9
	;;
	buster)
		DEBVER=10
	;;
	bullseye|stable)
		DEBVER=11
	;;
	bookworm|testing)
		DEBVER=12
	;;
	trixie)
		DEBVER=13
	;;
	forky)
		DEBVER=14
	;;
	sid|unstable)
		DEBVER=999
	;;
	*)
		die "unrecognized Debian release: $SUITE"
	;;
esac

KERNEL_ARCH=$ARCHITECTURE
case "$ARCHITECTURE" in
	armhf)
		KERNEL_ARCH=armmp
	;;
	i386)
		KERNEL_ARCH=686-pae
	;;
	mips64el)
		KERNEL_ARCH=5kc-malta
	;;
	mipsel)
		KERNEL_ARCH=4kc-malta
	;;
	ppc64el)
		KERNEL_ARCH=powerpc64le
	;;
esac

if ! check_skip kernel; then
	set -- "--include=?or(?exact-name(linux-image-cloud-$KERNEL_ARCH),?exact-name(linux-image-$KERNEL_ARCH))" "$@"
fi

if test -n "$SSHKEY"; then
	set -- --include=openssh-server "$@"
fi

if ! check_skip systemdnetwork; then
	# add a DNS resolver
	set -- \
		'--include=?exact-name(libnss-resolve)' \
		"--customize-hook=$SHARE_DIR/customize-resolved.sh" \
		"$@"
fi

# construct mmdebstrap options as $@:
set -- \
	--verbose \
	--variant=apt \
	--format=ext2 \
	--include=init \
	"--architecture=$ARCHITECTURE" \
	'--customize-hook=echo "LABEL=debvm / ext4 defaults 0 1" >"$1/etc/fstab"' \
	"$@"

# set up a hostname
set -- \
	"--customize-hook=echo $VMNAME >"'"$1/etc/hostname"' \
	"--customize-hook=echo 127.0.0.1 localhost $VMNAME >"'"$1/etc/hosts"' \
	"$@"

# allow password-less root login
set -- '--customize-hook=chroot "$1" passwd --delete root' "$@"

if ! check_skip systemdnetwork; then
	# dhcp on all network interfaces
	set -- "--customize-hook=$SHARE_DIR/customize-networkd.sh" "$@"
fi

# add ssh key for root
if test -n "$SSHKEY"; then
	set -- \
		'--customize-hook=mkdir -m700 -p "$1/root/.ssh"' \
		"--customize-hook=upload $SSHKEY /root/.ssh/authorized_keys" \
		"$@"
fi

if ! check_skip packagelists; then
	set -- --skip=cleanup/apt/lists "$@"
	set -- "--customize-hook=$SHARE_DIR/customize-dpkgavailable.sh" "$@"
fi

if test "$DEBVER" -le 8; then
	# Use obsolete and expired keys.
	set -- '--keyring=/usr/share/keyrings/debian-archive-removed-keys.gpg' "$@"
	set -- --aptopt='Apt::Key::gpgvcommand "/usr/libexec/mmdebstrap/gpgvnoexpkeysig"' "$@"
	set -- --hook-dir=/usr/share/mmdebstrap/hooks/jessie-or-older "$@"
fi

if test "$DEBVER" -ge 12 && ! check_skip usrmerge; then
	# Avoid the usrmerge package
	set -- --hook-dir=/usr/share/mmdebstrap/hooks/merged-usr "$@"
fi

set -- "--customize-hook=$SHARE_DIR/customize-autologin.sh" "$@"

set -- "$SUITE" "$IMAGE" "$@"

set -ex

mmdebstrap "$@"

IMAGESIZE=$(stat -c %s "$IMAGE")
if test "$IMAGESIZE" -lt "$SIZE"; then
	truncate -s "$SIZE" "$IMAGE"
	/sbin/resize2fs "$IMAGE"
fi
/sbin/tune2fs -L debvm -i 0 -O extents,uninit_bg,dir_index,has_journal "$IMAGE"
# Must fsck after tune2fs: https://ext4.wiki.kernel.org/index.php/UpgradeToExt4
/sbin/fsck.ext4 -fDp "$IMAGE"