#!/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.


[[ $EUID == 0 ]] || exec sudo -E "${BASH_SOURCE[0]}" "$@"


if ! test "$BASH_VERSION"; then echo "error: shell is not bash" >&2; exit 1; fi
shopt -s inherit_errexit 2>/dev/null ||: # ignore fail in bash < 4.4
set -eE -o pipefail
trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" exit status: $?, PIPESTATUS: ${PIPESTATUS[*]}" >&2' ERR

usage() {
  cat <<'EOF'
Usage: chboot [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, boot_debianjessie.

For a system without libreboot, which is failing completely to
boot on one distro, here is how I did a chboot for it:
# arch-pxe had been run previously
pxe-server some_hostname arch
# reboot some_hostname into arch live env
pxe-server # disable pxe server
ssh root@some_hostname
lsblk # identify boot dev. if boot dev is a raid, this could be repeated on all boot devs.
mount /dev/sdd3 /mnt
mp=/mnt/boot_debiantesting # the subvol i want to chboot to
boot_disk=/dev/sdd
grub-bios-setup -d $mp/grub/i386-pc -s -m $mp/grub/device.map $boot_disk
reboot

todo: figure out if it's possible to make a multi-distro grub like I have with libreboot
for non-libreboot systems

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

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



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


distro=$1

mnt=/boot
if ! mountpoint $mnt &>/dev/null; then
  mnt=/
fi

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

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


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

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

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

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

for boot_dev in $(btrfs fil show $mnt | sed -nr 's#.*path\s+(\S+)$#\1#p'); do

  mount_point=$(mktemp -d)

  e mount -o subvol=$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
  e umount $mount_point
done

if [[ $(blockdev --getsize64 ${boot_disk}4) == 8388608 ]]; then
  # old partition scheme
  grub_dev=${boot_disk}4
elif [[ $(blockdev --getsize64 ${boot_disk}5) == 8388608 ]]; then
  grub_dev=${boot_disk}5
else
  grub_dev=${boot_disk}7
fi

e mount $grub_dev $mount_point
e grub-editenv $mount_point/grubenv set last_boot=/$distro
e grub-editenv $mount_point/grubenv set did_fai_check=true
e umount $mount_point
if $reboot; then
  touch /tmp/keyscript-off
  reboot now
fi