#!/bin/sh
#
#       Copyleft 2012 Gui Iribarren <gui@altermundi.net>
#       
#       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 3 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.
#
###  
###  Usage: $0 [ [-w time] | now ] [-f time]
###  
###  $0 falls back to a last-known-good config after an ill-fated reboot.
### 
###  It makes a backup of /etc, and after the grace time reboots the system. 
###    At the next boot, it waits again for a fallback timeout; if you can't
###    login and delete the backup, it will restore it and reboot.
###  This mechanism makes it possible to run $0, try risky operations (like 
###    restarting the network), and if something goes wrong so you can't
###    login, just wait for the fallback timeout.
###  Even more, you can make actual changes to /etc config and reboot. If it
###    comes up right, you can login and simply delete the backup
###    /.etc.last-good.tgz . But if something went wrong with the new /etc, 
###    again just wait for the revert timeout.
###  
###  -w, --wait, --in TIME
###        After backing up /overlay/upper/etc, wait for TIME before reboot.
###          Default: 5min
###  -f, --fallback-after TIME
###        After boot, wait for TIME before reverting /overlay/upper/etc from
###        backup found in /overlay/upper/.etc.last-good.tgz
###          Default: 10min
###  now
###        Do not make /overlay/upper/etc backup; instead check that there's
###        one already in place (/overlay/upper/.etc.last-good.tgz), then reboot
###        and wait for fallback timeout.
###  cancel
###        Remove /overlay/upper/.etc.last-good.tgz
###        (useful after a successful reboot)
###  discard
###        Restores /overlay/upper/etc from /overlay/upper/.etc.last-good.tgz.
###        (useful to discard changes)
### 
###    TIME examples: 1hour 60min 60m 3600sec 3600
###    (all of them are equivalent)
###
#
#

PIDFILE="/tmp/run/safe-reboot.pid"
fallback_timeout=600
grace_period=300
file_etc_lastgood="/overlay/upper/.etc.last-good.tgz"
dir_etc="/overlay/upper/etc/"
safe_fallback_script="/overlay/upper/etc/init.d/safe-fallback"
safe_fallback_script_enable="ln -sf ../init.d/safe-fallback /overlay/upper/etc/rc.d/S11safe-fallback"
cmd_force_reboot="echo b > /proc/sysrq-trigger" # Immediately reboot the system without syncing or unmounting disks.

usage () { reason="$*"
  [ -n "$reason" ] && echo "$reason"
  sed -n "/^### /{s///;s|\$0|$(basename "$0")|g;p}" "$0"
  exit 1
}

timetoseconds() { # valid and equivalent input examples: 3600 3600s 3600sec 60minutes 1ho
        local time="$1" ; local seconds

        { [ "${time%s*}" -ge 0 ] 2> /dev/null && seconds="${time%s*}"; } \
      ||{ [ "${time%m*}" -ge 0 ] 2> /dev/null && seconds="$((${time%m*}*60))"; } \
      ||{ [ "${time%h*}" -ge 0 ] 2> /dev/null && seconds="$((${time%h*}*3600))"; }
      
        echo $seconds
}

backup_etc_exists () {
  [ -s "$file_etc_lastgood" ]
}

backup_etc () {
  rm -f "$file_etc_lastgood"
  tar -czf "$file_etc_lastgood" -C "$dir_etc" .
}

write_safe_fallback_script () {
  mkdir -p "$(dirname "$safe_fallback_script")"
  rm -f "$safe_fallback_script"
  touch "$safe_fallback_script"
  chmod +x "$safe_fallback_script"
  cat <<EOF > "$safe_fallback_script"
#!/bin/sh /etc/rc.common
START=11
start() {
  ( [ -s "$file_etc_lastgood" ] \
    && sleep $fallback_timeout & trap 'kill \$! ; exit' TERM ; wait \
    && if [ -s $file_etc_lastgood ] ; then
        safe-reboot discard
    fi ) &
  echo \$! > "$PIDFILE"
}
EOF
  mkdir -p "$dir_etc"/rc.d/
  $safe_fallback_script_enable
}

reboot_after_grace_period () {
  sleep $grace_period & trap 'kill $! ; exit' TERM ; wait
  write_safe_fallback_script
  reboot ; sleep 10 ; eval "$cmd_force_reboot"
}

action_cancel () {
  rm -f "$file_etc_lastgood"
  rm -f "$safe_fallback_script"
  echo -n "Removed $file_etc_lastgood, "
  if [ -s "$PIDFILE" ] ; then
    kill "$(cat "$PIDFILE")"
    rm -f "$PIDFILE"
    echo "and killed running timeout."
  else
    echo "no running timeout found."
  fi
}

action_discard () {
  if backup_etc_exists ; then
    rm -f "$safe_fallback_script"
    rm -rf $dir_etc ; mkdir -p $dir_etc
    tar -xzf $file_etc_lastgood -C $dir_etc
    rm -f $file_etc_lastgood
    reboot ; sleep 10 ; eval "$cmd_force_reboot"
  else
    echo "STOP! Backup file $file_etc_lastgood not found or 0 sized! Refusing to continue."
    exit 2
  fi
}

while [ -n "$1" ]; do
  arg="$1"
  shift
  case "$arg" in
    --in | in | --wait | wait | -w ) grace_period=$(timetoseconds "$1") ; shift
      [ -z "$grace_period" ] && usage "Error with grace period value."
    ;;
    --fallback-after | -f ) fallback_timeout=$(timetoseconds "$1") ; shift
      [ -z "$fallback_timeout" ] && usage "Error with fallback timeout value."
    ;;
    --discard | discard ) action_discard ; exit ;;
    --cancel | cancel ) action_cancel ; exit ;;
    now ) grace_period=0 ;;
    --help | -h ) usage ;;
  esac
done

if [ "$grace_period" -eq 0 ] ; then
  backup_etc_exists || { echo "STOP! Backup file $file_etc_lastgood not found! Refusing to continue." ; exit 2 ; }
else
  backup_etc_exists && { echo "STOP! Backup file $file_etc_lastgood exists! You probably want to \`$0 now\`" ; exit 4 ; }
  backup_etc || { echo "STOP! Backup failed. Refusing to continue." ; exit 8 ; }
fi

write_safe_fallback_script || { echo "STOP! Writing fallback script failed. Refusing to continue." ; exit 16 ; } 
reboot_after_grace_period & { echo "Rebooting in $grace_period seconds..." ; }
echo $! > "$PIDFILE"