#!/bin/bash
# Copyright (C) 2016 Ian Kelling

# This program 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
# of the License, or (at your option) any later version.

# This program 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 program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.


set -eE -o pipefail
trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" returned $?" >&2' ERR

[[ $EUID == 0 ]] || exec sudo "$BASH_SOURCE" "$@"

usage() {
    cat <<EOF
Usage: ${0##*/} [OPTIONS] DISTRO_NAME
Set grub to boot into a different distro, and reboot unless -r

With no argument, print available distros
DISTRO_NAME is based on the partition names in /boot.
For example debianjessie for the partitionn boot_debianjessie.

-r         Do not reboot.
-d         Enable debug output.
-h|--help  Print help and exit.

Note: Uses GNU getopt options parsing style
EOF
    exit $1
}


grub_extn=4

###### begin command line parsing #####
reboot=true
temp=$(getopt -l opt o "$@") || usage 1
eval set -- "$temp"
while true; do
    case $1 in
        -d) set -x; shift ;;
        -r) reboot=false; shift ;;
        -h|--help) usage ;;
        --) shift; break ;;
        *) echo "$0: Internal error!" ; exit 1 ;;
    esac
done


distro=$1

if [[ ! $distro ]]; then
    echo "available distros:"
    cur=$(btrfs subvol show /boot| sed -rn 's/^.*Name:\s*(\S*).*/\1/p')
    btrfs subvolume list /boot | awk '{print $9}' | sed "s/$cur/$cur (current)/"
    exit 0
fi

###### end command line parsing #####


#### begin initial error checking #####

if ! btrfs subvolume list /boot | grep "_$distro$" &>/dev/null; then
    echo "$0: error: _$distro$ not found in btrfs subvolume list /boot:"
    btrfs subvolume list /boot
    exit 1
fi

#### end initial error checking #####

e() { echo "$@"; "$@"; }

boot_dev=$(mount | sed -rn "s#^(\S+) on /boot .*#\1#p")

mount_point=$(mktemp -d)

e mount -o subvol=boot_$distro $boot_dev $mount_point

boot_disk=${boot_dev%%[0-9]*}

# arch doesn't have $mount_point/grub/device.map, accoring to the grub manual,
# it just generates one if the file doesn't exist.
# https://www.gnu.org/software/grub/manual/html_node/Device-map.html
e grub-bios-setup -d $mount_point/grub/i386-pc -s -m $mount_point/grub/device.map $boot_disk

# todo, mount_point needs subvolid=0

e umount $mount_point

e mount $boot_disk$grub_extn $mount_point
e grub-editenv $mount_point/grubenv set last_boot=/boot_$distro
e grub-editenv $mount_point/grubenv set did_fai_check=true
e umount $mount_point
e rmdir $mount_point

if $reboot; then
    touch /tmp/keyscript-off
    reboot now
fi